Ecological Research Series
PLAN AND CONCEPTS FOR MULTI-USE
MANAGEMENT OF THE
ATCHAFALAYA BASIN
Environmental Monitoi
Office of Research and Development
U.S. Environmental Protection Agency
Las Vegas, Nevada 89114
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RESEARCH REPORTING SERIES
Research reports of the Office of Research and Development, U.S. Environmental
Protection Agency, have been grouped into nine series. These nine broad cate-
gories were established to facilitate further development and application ot en-
vironmental technology. Elimination of traditional grouping was consciously
planned to foster technology transfer and a maximum interface in related fields.
The nine series are:
1. Environmental Health Effects Research
2. Environmental Protection Technology
3. Ecological Research
4. Environmental Monitoring
5. Socioeconomic Environmental Studies
6. Scientific and Technical Assessment Reports (STAR)
7. Interagency Energy-Environment Research and Development
8. "Special" Reports
9. Miscellaneous Reports
This report has been assigned to the ECOLOGICAL RESEARCH series. This series
describes research on the effects of pollution on humans, plant and animal spe-
cies and materials. Problems are assessed for their long- and short-term influ-
ences Investigations include formation, transport, and pathway studies to deter-
mine the fate of pollutants and their effects. This work provides the technical basis
for setting standards to minimize undesirable changes in living organisms in the
aquatic, terrestrial, and atmospheric environments.
This document is available to the public through the National Technical Informa-
tion Service, Springfield. Virginia 22161.
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EPA-600/3-77-062
May 1977
PLAN AND CONCEPTS FOR MULTI-USE MANAGEMENT
OF THE ATCHAFALAYA BASIN
by
Johannes L. van Beek
William G. Smith
James W. Smith
Philip Light
Coastal Environments Inc.
1260 Main Street
Baton Rouge, Louisiana 70802
Contract No. 68-01-2299
Project Officers
Harold V. Kibby
(Project Officer through August 1975)
Corvallis Environmental Research Laboratory
Corvallis, Oregon 97330
Victor W. Lambou
(Project Officer from September 1975 to Present)
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
ENVIRONMENTAL MONITORING AND SUPPORT LABORATORY
LAS VEGAS, NEVADA 89114
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DISCLAIMER
This report has been reviewed by the Environmental Monitoring and Support
Laboratory-Las Vegas, U.S. Environmental Protection Agency, and approved for
publication. Approval does not signify that the contents necessarily reflect
the views and policies of the U.S. Environmental Protection Agency, nor does
mention of trade names or commercial products constitute endorsement or recom-
mendation for use.
ii
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FOREWORD
Protection of the environment requires effective regulatory actions
which are based on sound technical and scientific information. This Informa-
tion must include the quantitative description and linking of pollutant
sources, transport mechanisms, interactions, and resulting effects on man
and his environment. Because of the complexities Involved, assessment of
specific pollutants in the environment requires a total systems approach
which transcends the media of air, water, and land. The Environmental
Monitoring and Support Laboratory-Las Vegas contributes to the formation and
enhancement of a sound integrated monitoring data based through multi-
disciplinary, multimedia programs designed to:
• develop and optimize systems and strategies for moni-
toring pollutants and their impact on the environment
• demonstrate new monitoring systems and technologies by
applying them to fulfill special monitoring needs of
the Agency's operating programs
This report presents plans and concepts for multi-use management of the
Atchafalaya Basin surface waters. The U.S. Environmental Protection Agency,
the U.S. Army Corps of Engineers, the U.S. Department of the Interior, the
State of Louisiana, special interest groups, and other interested individuals
will use this information to assess the potential impact of a massive chan-
nelization project proposed by the Corps and to develop alternative land
and management plans, which will accommodate flood-flows and maintain an
acceptable level of environmental quality. For further information contact
the Water and Land Quality Branch, Monitoring Operations Division.
George B. Morgan
Director
Environmental Monitoring and Support Laboratory
Las Vegas
ill
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TABLE OF CONTENTS
..................... iii
FOREWORD ..............................................
..... vi
LIST OF FIGURES .............................................
......... ix
LIST OF TABLES ...........................................
ABBREVIATIONS [[[
CONVERSION TABLE [[[ xi
...... v-j -f
ACKNOWLEDGEMENTS ................................................
SUMMARY [[[ l
I. INTRODUCTION .............................................
Regional Setting .................................... ;?
Statement of Regional Problem ....................... ^
Objectives and Relationship to Other Studies ........ 7
Approach ............................................
II. CONCLUSIONS AND RECOMMENDATIONS .......................... 14
III. REQUIREMENTS OF THE SOCIO-ECONOMIC COMPLEX ............... 17
Flood Control ....................................... JJ
Urban and Industrial Development .................... ^
Agriculture and Rural Settlement .................... 28
Oil and Gas ......................................... 31
Recreation .......................................... 32
IV. FORESTS OF THE ATCHAFALAYA BASIN .......................... 35
General Nature of the Atchaf alaya Basin ............. 35
Conditions in the Bottomland Forests ................ 40
Flooding and Sedimentation Tolerances ............... 45
Forest Types ........................................ 4
Forestry Potential ..................................
V. FISH AND WILDLIFE RESOURCES
Factors Enhancing Fish Production
Factors Enhancing Crawfish Production
Waterfowl
,~
Furbearers ....................................... * " ,ft
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VI. LOWER ATCHAFALAYA BASIN • 83
Terrebonne Marshes 83
Atchafalaya Delta 86
VII. BASIN HYDROGRAPHY AND HYDROLOGY 89
Verret and Fausse Point Basins 89
Atchaf alaya Basin Floodway 92
Sub-Basin Hydrographs and Hydroperiods 97
Water Balance, Yield, and Storage 116
VIII. THE PRESENT AND FUTURE MAIN CHANNEL 132
Channel Dimensions 132
Hydraulic Geometry 137
Probable Natural Channel 1*3
IX. PLAN FOR MANAGEMENT OF THE ATCHAFALAYA BASIN 150
Definition of Management Zones 150
Strategies for Management 152
Protective Use Zone 153
Buffer Zone • • • 156
Exploitative Use Zone 157
Surface Water Management 159
Flood Control and Protection 159
Management of the Fluvial Svamps 164
Management at Unit Level 165
Management of the Coastal Area 177
REFERENCES 182
BIBLIOGRAPHY 189
APPENDICES 197
Appendix A 197
Appendix B .................* •••
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LIST OF FIGURES
Page
Figure No.
2-1 Atchafalaya Basin location map 4
2-2 Major environments within the Atchafalaya 10
Basin
2-3 Division of Atchafalaya Basin into management 11
units
3-1 Flood control aspects of Atchafalaya Basin 18
3-2 Changes in mean elevation for three management
units 21
4-1 Trends of suspended sediment concentration for
the Mississippi River and Atchafalaya River 39
4-2 Forest types in Buffalo Cove Management Unit 50
6-1 Extent of marsh replacement by shallow water
bodies 84
7-1 Flood frequency in the Atchafalaya Basin 90
7-2 Diversion of Atchafalaya River flow 93
7-3 Locations of U.S.C.E. topographic survey ranges
and stage gaging stations 96
7-4 Stage-discharge relationships at Upper Grand Lake for
conditions at present and after proposed Center
Channel dredging
7-5 Stage hydrographs of Buffalo Cove Management
Unit "
7-6 Flooding characteristics of Pigeon Bay Manage-
ment Unit 104
7-7 Flooding characteristics of Bayou Fordoche
Management Unit 105
7-8 Flooding characteristics of Cocodrie Manage-
ment Unit 106
7-9 Flooding characteristics of Beau Bayou Manage-
ment Unit 107
vi
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Figure No.
Page
7-10 Flooding characteristics of Buffalo Cove
Management Unit log
7-11 Flooding characteristics of Bayou des Glaises
Management Unit 10
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135
Figure No.
8-3 Width and mean depth of Main Channel at bank-
full stage
8-4 Relationships between mean depth, width, mean
velocity and discharge of Atchafalaya River
at Simmesport
8-5 Stage-discharge relationship for Atchafalaya
River at Simmesport
8-6 Cross sections of Atchafalaya River at Simmes-
port at mile 4.8
8-7 Cross sections of Atchafalaya River at Simmes-
port at mile 4.8 as obtained from calculations
for various discharges
8-8 Water- surf ace profiles along Main Channel 145
8-9 Trends of river stage for Lower Atchafalaya River
at Morgan City and Wax Lake Outlet at Calumet
8-10 Cross sections of Atchafalaya River Main Channel
at mile 75.1
9-1 Proposed zonation of protective and exploitative
land uses
9-2 Proposed management of surface water for mul-
tiple and compatible use of the Atchafalaya
Basin resources
9-3 Schematic summary of water management plan
9-4 Schematic representation of floodway management
units and water routing
1 A O
viii
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LIST OF TABLES
Table No.
Page
3-1 Average sediment balance, 1965 - 1971 for
Atchafalaya Basin Floodway 22
7-1 Present and future averages of water levels,
West Floodway 10Q
7-2 Present and future averages of water levels,
East Floodway 101
7-3 Relationship between flooding characteristics
and biological conditions and values 103
7-4 Areas subject to given hydroperiod class within
floodway management units 114
7-5 Pertinent data, water management units 124
7-6 Water yield computation, Buffalo Cove Management
Unit 126
7-7 Normal monthly water yield in management units on
west side of floodway 127
7-8 Normal monthly water yield in management units on
east side of floodway 128
8-1 Flow parameters, Atchafalaya River 140
9-1 Water budget, regulated management units, West
Atchafalaya Floodway 172
9-2 Water budget, regulated management units, East
Atchafalaya Floodway 174
9-3 Summary of supplemental flow requirements 178
9-4 Summary of return flows 179
ix
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LIST OF ABBREVIATIONS
cfs ........... cubic feet per second
cm ........... centimeter (s)
cms ........... cubic meters per second
EPA ,.,. s „ * *.%... U.S. Environmental Protection Agency
ft ........... square feet
floodway
Gulf Intracoastal Waterway
g/1 ........... grams per liter
in ........... inch(es)
kilograms
square kilometers
pounds
m ............ meters
y ............ micron (s)
m2 ........... square meter (s)
m3 ........... cubic meter (s)
mg ........... milligrams
mg/l .......... milligrams per liter
mi2 ........... square miles
ml ........... milliliters
nun2 ........... square millimeters
mos, mths ..... « . . months
HSL ....... mean sea level
N I * | ........ nitrogen
NSTL .......... National Space Technology Laboratories
p ............ phosphorus
ppm ........... parts per million
USCE .......... U.S. Army Corps of Engineers
USDA '. ......... U.S. Department of Agriculture
.......... U.S. Department of the Interior
'. '. ........ cubic yards
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CONVERSION FACTORS
Symbol
u
mm
m
m
km
ha
2
m
2
m
km2
3
m
ml
1
mg
g
kg
When you know
microns
millimeters
meters
meters
kilometer
hectares
square meters
square meters
square kilometer
cubic meters
milliliter
liter
milligrams
grams
kilograms
Multiply by
0.00003937
0.0393701
3.28084
1.09361
0.621371
2.47105
10.76
1.19599
0.3861
35.31
0.033818
1.05669
0.00003527
0.03527
2.30462
To find
inches
inches
feet
yards
miles
acres
square feet
square yards
square miles
cubic feet
ounces
quarts
ounces
ounces
pounds
Symbol
in
in
ft
yd
mi
acre
ft2
yd2
mi2
ft3
oz
Qt
oz
oz
Ib
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ACKNOWLEDGEMENTS
Formulation of the concepts and plans put forward in the present
report would not have .been possible without the help and cooperation
we have received from a number of individuals and agencies. For this
help we are most grateful.
Mr. Frank Shropshire of the Southern Hardwoods Laboratory, U.S.
Forest Service, provided valuable information with regard to tolerances
and possible enhancement of the forest communities as related to annual
flooding and sedimentation.
Discussion with personnel of the Louisiana Wild Life and Fish-
eries Commission aided us in evaluating present fish and wildlife
resources of the Atchafalaya. We thank especially Mr. Greg Linscomb
in this regard.
Much of the hydrologic data used in plan development was pro-
vided by the Hydraulics Branch of the U.S. Corps of Engineers New
Orleans District. Data retrieval was greatly facilitated by the
cooperation of USCE personnel, in particular Mr. Bill Garret.
Equally important have been the guidance in problem definition
and the critical review provided by the EPA Project Officers under
whose supervision the research was undertaken. We wish to sincerely
thank Mr. Victor Lambou, EPA, Las Vegas, Nevada, and Dr. Harold V.
Kibby, EPA, Corvallis, Oregon, for their continuous and constructive
criticism.
The study was made in collaboration with a number of members
of the Coastal Environments, Inc., staff, including Alice R. Franklin,
and Penny Culley. Dr. Sherwood M. Gagliano provided
invaluable guidance and criticism throughout the study. Cartography
was done by Curtis Latiolais, and editing by Peggy King.
xii
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SUMMARY
This study centers on conflicts between human use and environ-
mental quality of the Atchafalaya Basin, Louisiana, as related to
surface waters. Most eminent in the Atchafalaya Basin are the bio-
logical resources constituted by its bottomland and swamp environ-
ments. Existence and long-term use of these resources are increasingly
endangered as a result of human action related to use of the area's
land and waters for flood control, urban and industrial development,
navigation, agriculture, and mineral extraction. In addition, cultural
uses also have become mutually incompatible. Further rapid deteriora-
tion of environmental quality must be anticipated if necessary author-
ized flood control measures, in particular stream channelization, are
not brought in agreement as much as possible with natural resource and
cultural values and if no measures are taken to achieve a distribution
of present and future uses that takes into account the constraints
placed by the natural setting.
Mutual conflicts between the various uses present in the Atcha-
falaya Basin have a common denominator in that they largely arise from
incompatible requirements with regard to surface water management. A
study was, therefore, undertaken to develop a plan for management of
surface water that allows, as much as possible, compatible use of the
basin's many resources. Following initial research, which focused on
identification of the basin's environments and the manner in which
their aggregate characteristics are controlled and affected by natural
processes and various human uses,1 the present report's starting point
is the determination of surface water requirements of the natural re-
source complex, including fishes, wildlife, and forests, and the socio-
economic resource uses, including flood control, urban and industrial
development, mineral extraction, transportation, agriculture, and
recreation.
The most general requirements are 1) reduction of sedimentation
to preserve floodway capacity and aquatic habitats, 2) improvement of
water quality, 3) provision of flood protection for existing develop-
ment in the Morgan City - Lake Verret area, 4) reduced flooding of
the Terrebonne marshes, 5) separation of deep water access to Morgan
City from the developing Atchafalaya Delta, 6) management of surface
water runoff from developed natural levee ridges surrounding the
swamp environment, 7) limitation of expansion of exploitative uses
from the natural levee ridges into marginal swamps, and 8) integration
into rather than superposition on the swamp environment of mineral
industry canals. For the Atchafalaya Basin Floodway, requirements
Coastal Environments, Inc., Environmental Base and Management
Study: Atchafalaya Basin, Louisiana (Through Center for Wetland Re-
sources, Louisiana State University for the U. S. Environmental Pro-
tection Agency, 1974a), 228 p.
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are expressed In terms of desirable annual water level variation, and
resulting hydrographs are compared with those for present and pro-
posed conditions associated with channelization. Furthermore, simul-
taneous consideration of topography and hydrographs allowed determina-
tion of areas experiencing specific hydroperiods under the above three
conditions, present, proposed and managed, with hydroperiods related
to swamp habitats. Additionally, water availability from rainfall
was calculated on a monthly basis in order to determine the extent
to which river water could be substituted by local runoff so as to
reduce the Influx of fluvial sediment. Minimum volumetric inflow re-
quirements were calculated on the basis of storage characteristics and
water levels as attained at present.
Hydraulic geometry of the present main river channel is
analyzed, and those channel dimensions that are in equilibrium with
bankfull discharge are determined. Assuming this discharge to be the
controlling factor in further natural channel development, the most
probable natural stream profile is calculated, and associated channel
dimensions are compared with proposed dimensions following channeliza-
tion. The analysis suggests that channel enlargement through dredging
should not go beyond a cross-sectional area of 7,400 square meters*
(m2) or 80,000 square feet (ft2) as expressed below project floodflow
line. Exceedence of this dimension is likely to lead to voluminous
dredging and spoil disposal requirements unless the channel is con-
fined by artificial levees.
On the basis of general water management requirements for the
Atchafalaya Basin as a whole and specific requirements for the flood-
way swamps, a multi-use management plan is developed. First, manage-
ment zones are defined, with each incorporating as many possible
existing land uses that are compatible with the primary management
objectives. Management zones are grouped into categories of pro-
tective use, which includes mostly the forest and aquatic habitats,
exploitative use (where substantial development has already occurred)
and a buffer zone whose function is to minimize conflicts between
exploitative and protective uses. Strategies for management of each
of the above zones are set forth. Having defined a compatible dis-
tribution of land uses, a surface water management plan is presented
that is believed to provide for maximum longevity of the remaining
swamp ecosystem, to minimize the conflict arising from flood control
needs, and to make possible compatible derivation of benefits from
both renewable and non-renewable resources.
* See Appendix for conversion to metric measure.
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I
INTRODUCTION
Regional Setting
n*fnrJh? Atchaf«lay« Basin ±s an 1,800-square mile lowland between
natural levee ridges of present and former Mississippi River courses
in southcentral Louisiana (Figure 2-1). The natural basin extends
northward for some 120 miles from the Gulf of Mexico between the
levee ridges of Bayous Cypremort and Teche to the west and Bayou du
Large, Bayou Lafourche, and the Mississippi River to the east. Central
to the basin is the Atchafalaya River, which carries the combined flow
of the Red River and part of the Mississippi River into Atchafalaya
Bay. The basin is naturally divided by the east-west oriented levee
ridge of Bayou Teche at the latitude of Morgan City. To the south of
this ridge, the basin has an estuarine character dominated by fresh
to brackish marshes and water bodies. To the north, freshwater en-
vironments dominate, ranging from swamp forest to bottomland hardwoods
depending on topography and related hydroperiods .
f ,u °f mfj°r consetluence with regard to natural setting is the use
of the Atchafalaya Basin in flood control of the lower Mississippi
valley. Paralleling the Atchafalaya River at an average distance of
8 miles from the river, guide levees extend southward from the
Mississippi River near Simmesport to the Teche ridge. These levees
and the intermediate area constitute the Atchafalaya Basin Floodway.
Control structures at the Mississippi River allow for diversion of
Mississippi River water into the floodway as a relief measure. Water
Mnr« rf? ided thr°Ugh the basin into the Lower Atchafalaya River at
OuMp? H ^K^ ut0 3n addltional »annade channel, the Wax Lake
Outlet, both of which discharge into Atchafalaya Bay.
north nh effectively ^gment the natural basin
north of the Teche ridge in a central area adjacent to the Atchafalaya
River, and an eastern and western area (continued between the guide
levees and the basin's natural boundaries), the Verret and Fausse
Point Basins, respectively (Figure 2-1). As a result, the central
floodway area is largely dominated by riverine forms and processes
and subject to annual overflow, whereas input of water and materials
and water level changes in the adjacent sub-basins are predominantly
a function of local runoff.
T , , ^ Atchafalaya Basin has experienced much environmental change.2
Initial changes were related to increasing natural diversion of
Mississippi River water and sediment into the Atchafalaya River and
an associated intensification of riverine processes throughout the
2Ibid.
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fltchofolaya Basin. La
Figure 2-1. Atchafalaya Basin in southcentral Louisiana as
confined by Bayous Teche and Cypremort to the
west and by the Mississippi River, Bayou La-
fourche, and Bayou du Large to the east.
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basin. Through lacustrine delta building, many of the extensive lakes
formerly existing along the axis of the basin were gradually filled
and replaced by swamp forest communities. The river became engaged in
building a floodplain with a well-defined, natural-levee-bounded
channel and backwater areas in which remaining lakes would be bypassed
by sedimentation and new lakes would form as a result of natural pond-
ing. However, before such an environment could be fully realized,
natural processes and trends were modified greatly. Water levels
became subject to greater fluctuation as flows were confined to the
central part of the natural basin through construction of floodway
levees. Channelization of the Main Channel and four major distribu-
taries, together with associated spoil deposition, forced change in the
water distribution mode from overbank flow to channel flow. These
combined interventions redirected sedimentation from the natural levees
to backwater areas, thus reducing the trend toward natural topographic
and habitat diversity. At the same time, they accelerated the rate of
southward channel development so that increasing volumes of sediment
are now carried into Atchafalaya Bay, where a marine delta is presently
emerging. Within the central part of the Atchafalaya Basin, change
from a natural to an artificial floodway has set in motion a trend from
natural and diversified floodplain development toward a more uniform
terrestrial habitat.
In contrast to the floodway segment, change of the Verret and
Fausse Point Basins has been greatly retarded as a result of severance
from riverine processes. Large water bodies such as-Lake Verret, Lake
ralourde, and Lake Fausse Point have been retained, as have the exten-
sive swamp forests.
Statement of Regional Problem
Against the above setting, the regional problem underlying the
present study can be discussed. This problem centers on human use of
the area s resources and quality of its environment as they relate to
surface water. Inherent to the geologic and general natural setting,
the Atchafalaya Basin is extremely rich in both renewable and non-
renewable resources. Most eminent are the biological resources. The
bottomland hardwoods, swamp forests, and associated water bodies
provide habitats for greatly varied and extensive populations of
wildlife, including endangered species and fishes.3 Together these
elements constitute a renewable resource of food, raw materials, and
recreation that, considering its magnitude, is of national importance.
In addition, the Atchafalaya Basin's primary production is likely to
contribute substantially to marine fisheries through export of
tMtj^?1'8' DePartment of the Interior. A Progress Report; Fish.
Wildlife, and Related Resources, Atchafalaya River Basin. Louisiana
(1974), 195 p.
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detrltal matter from the basin to adjacent watera of the Gulf of
Mexico.
The above complex of resources has evolved and is maintained
predominantly through natural processes. In that regard, they
contrast with a second complex of the basin's resources, use of
which has necessitated man's interference with the natural environment.
This second complex includes the (artificially or naturally) better-
drained lands along the margins of the basin used for agricultural,
industrial, urban, and transportation development, the natural water-
ways which have been modified for navigation and flood control, the
space used for flood control, and the oil and gas deposits which
invoked extensive canal dredging for transport and extraction.
Summarized from the above point of view, one may consider two
resource complexes, the first of which may be referred to as natural
resources, the second as socio-economic resources in the sense that
use in the present form is brought about by and relies predominantly
on socio-economic pressures and demands. As a result of the natural
setting of the area, requirements for maintenance and use of resources
in both complexes relate in the first instance to surface-water
aspects; these include quality, quantity, depth, seasonal and areal
distribution, and water level. Required surface-water conditions
differ greatly, however, between the two resource complexes, and to
some extent within a complex. These differences tend to be magnified
when, out of choice or necessity, the resource uses of the two
complexes become geographically intertwined in a pattern that disregards
contraints placed by the natural or socio-economic environments. This
is precisely what has happened in the Atchafalaya Basin, resulting in
the present regional problems and urgent need for management of surface
water and land use.
Within the middle floodway north of Morgan City, surface-water
problems stem from the conflict between the annual overbank flooding
and dewatering regime as required for fish, wildlife, forest, and
recreational purposes,* and the channelization, canal dredging, and
depositing of spoil. The latter actions, as associated with flood
control, navigation, and mineral extraction, have favored channel flow
at the expense of overbank flow, increasing siltation in lakes and back-
swamps and interrupting backwater circulation with adverse effects on
water quality.
In the upper floodway north of U. S. Highway 190, Atchafalaya
River levees have diminished flood frequency, allowing agricultural
development within the floodway with concomittant requirements for
better drainage and reduced diversion of Mississippi River water
Acoastal Environments, Inc., 1974a, o£.cit_.
-------
through the Atchafalaya Basin. This poses a dual conflict, namely be-
tween water requirements of the middle and upper floodway and require-
ments for agricultural and flood control use of land within the upper
floodway.
Containment of flood flows within the floodway—guide levees has
reduced flood threats to the Verret and Fausse Point Basins, allowing
expansion of agricultural development from the bounding natural levees
into adjacent wetlands. This has magnified the conflict between drain-
age requirements for agriculture and its associated runoff and require-
ments for annual water-level fluctuations and high-water quality of the
swamp ecosystem within these basins.
In the estuarine and deltaic part of the Atchafalaya Basin south
of the Teche ridge, requirements for resource use and maintenance are
equally conflicting under present conditions. In various ways, flood
control, mineral extraction, and navigation channels have allowed un-
controlled diversion of fresh water into the marshes and bays to the
east of Atchafalaya Bay, producing extensive and prolonged flooding
with resultant marsh-deterioration and adverse effects on productive
oyster grounds. A second conflict rapidly increases in magnitude with
accelerated growth of the Atchafalaya Delta. In view of rapid deteri-
oration of Louisiana's coastal environment, delta building is a highly
desirable process as a means of restoring renewable resources lost in
adjacent areas. Sediment is deposited, however, at the mouth of the
same channel required for deep-water access to industries in the Morgan
City area. Increased efficiency of the Atchafalaya River within the
floodway as required for flood control can only contribute to accelerated
sedimentation. Additionally, delta-progradation toward the Gulf of
Mexico will displace the river mouth seaward, thus progressively in-
creasing mean river-stages in the vicinity of Morgan City.
Objectives and Relationship to Other Studies
The conflicts of land use and surface water requirements, as dis-
cussed summarily in the preceding paragraphs, and the associated deteri-
oration of environmental quality and related natural resource base point
out the necessity for management of resource use in the Atchafalaya
Basin. This need has gained considerable urgency with pending plans
for further channelization of the Atchafalaya River to increase flood-
flow efficiency and of Bayous Chene, Bouef, and Black to improve navi-
gational access to fabrication yards of offshore drilling platforms.
To deal with the eminent regional problemst the U. S. Congress in
September, 1972, resolved that a land and water management study of the
Atchafalaya Basin be undertaken Jointly by the Army Corps of Eiigineers,
the Department of the Interior, and the U.S. Environmental Pro-
tection Agency. Central to this study is the objective to develop a
multi-use land and water management plan that allows compatible use of
the basin's resources. At the same time, knowledge gained through the
land and water management study is to aid in the evaluation of possible
adverse environmental effects that may be caused by further actions
-------
necessary to complete the Atchafalaya Basin Floodway Project as author-
ized by Congress in 1928. In particular, the effect of additional chan-
nelization of the Atchafalaya River and resultant modification of the
annual overflow regime are envisioned as having possible major con-
sequences with regard to fish, wildlife, and recreational resources.
Within the above framework, a number of closely related studies
have been undertaken of which the present study dealing more specifi-
cally with surface-water aspects of the Atchafalaya Basin is an integral
part. Initiated by the Environmental Protection Agency in 1973, the
study has had as its primary objective the development of a surface-
water management plan that allows compatible use of the basin's multi-
ple resources. Inherent to the nature and relative magnitude of the
problems, work has focused in particular on the designated use of the
central area as a floodway and associated modification of the overflow
regime versus the need to sustain the overflow swamps as one of the
basin's principal assets in regard to long-term benefits.
As a prerequisite to development of a surface-water management
plan, it is imperative that surface-water requirements are defined for
all major elements of the Atchafalaya Basin resources complex. Further-
more, it is necessary to understand the manner in which the basin
functions as a natural system and to identify trends and their rela-
tionship to both man-induced and natural processes. In this regard
and as an aide to evaluation of proposed flood control features, de-
velopment of an environmental base has been an equally important ob-
jective of the study.
Concurrent with the present effort and also within the framework
of the Atchafalaya Basin Land and Water Management Study, additional
investigations have been undertaken by the Environmental Protection
Agency, the Department of the Interior,5'6 and the Army Corps of
Engineers. Department of the Interior studies have been directed
largely toward development of a biological data base, with emphasis
on fish and wildlife resources and their respective habitats in the
floodway and Atchafalaya Bay. Resulting baseline data have been fully
utilized in the present study in determination of management require-
ments. Directed more specifically toward development of a surface-
water quality base and identification of annual variation and long-
term trends is an ongoing sampling program by the Environmental Pro-
tection Agency. In addition, a land-use suitability study for the
entire natural basin has been undertaken by the Army Corps of Engineers.
U. S. Department of the Interior, 1974, op. cit.
C. F. Bryan e_t^ al., Annual Report; A LimnoloRical Survey of
the Atchafalaya Basin (Louisiana Cooperative Fishery Unit, Louisiana
State University, 1974), 208 p.
-------
Of further benefit to the development of a land and water man-
agement plan for the Atchafalaya Basin has been the Involvement of
state agencies, particularly the Atchafalaya Basin Division of the
Department of Public Works and the Louisiana Wild Life and Fisheries
Commission. Building further on the approaches and data developed
through the above-mentioned research efforts, a special study was
undertaken through the Atchafalaya Basin Division to develop a de-
tailed management plan for the Buffalo Cove Swamp located within the
Atchafalaya Floodway, Development of this plan has, in turn, fur-
thered definition of management requirements for the overflow swamp
environment and understanding of the present resource-use conflicts.
A number of biological studies are presently funded by the Louisiana
Wild Life and Fisheries Commission.
Approach
Within the Atchafalaya Basin, natural processes and human action
have combined to produce an environmental differentiation, character-
ization of which has been the basis for both plan development and im-
pact analysis. The first phase of the water management study, under-
taken during 1973, focused largely on identification of the basin's
environments and the manner in which their aggregate characteristics
are controlled and affected by natural processes and various human
uses. Based on an analysis of process-environment relationships, the
natural basin was considered in terras of four environmental complexes:
channel, natural levee, flood basin, and marine deltaic. Each complex
is made up of a characteristic assemblage of natural elements, but
with cultural elements superimposed. Thus, for example, within a
floodplain complex one may identify such natural elements as swamp,
natural levees, abandoned channels, and lacustrine delta, each of
which also represents a definable habitat. Added to these, often
without regard to natural boundaries, may be manmade elements such as
canals or a highway. Environments, then, were viewed as the products
of specific processes which determine their mutual spatial relationship
and present characteristics as well as their rate and direction of
change. This allowed division of each complex into management units
within which environmental conditions as related to natural processes
and human use, and therefore management requirements, were similar
(Figures 2-2 and 2-3).
Within swamp management units, water levels and surface elevation
are the primary controls of biological habitat and suitability for
'Coastal Environments, Inc. Water Management Plan, Buffalo Cove
Swamp (Developed for the Atchafalaya Basin Division, Department of
Public Works of the State of Louisiana by Coastal Environments, Inc.,
1974b), 55 p.
-------
fttojor Environment/
Figure 2-2. Major environments within the Atchafalaya Basin
fined by process-form-habitat relationships.
as de-
[0
-------
Environmental
management Units
Figure 2-3. Division of Atchafalaya Basin into management units
the basis of natural environment and human use.
on
11
-------
urban, agricultural, and other land-based uses. Focusing on the flood-
way swamps, a method was developed to evaluate management units with
regard to habitat and possible uses based on the above two controls.
This involved the transformation of surface-elevation data into an
elevation frequency, or hypsometric curve, representative of a particu-
lar management unit. For a given water level, extent and depth of
submergence could in this manner be evaluated and provide a basis for
defining management options and evaluating impact of changed water-level
regimes.
Relationships between environments and hydrologic and sediment-
ary processes became sufficiently defined in the first study to allow
development of a basic approach to water management for the overflow
swamps within the floodway. This approach focussed particularly on
the reduction of sedimentation and maintenance of circulation. For the
basin as a whole, the first phase allowed a preliminary proposal of
guidelines for surface-water management as particularly related to the
conflict between use of the basin as a floodway and hydrologic require-
ments of the overflow swamps.
The second, present study builds further on the concepts and
methodology developed during the previous phase. It is, in all respects,
a continuation of the attempt to arrive at a management plan that allows
optimum use of the basin's resources and to analyze impact of proposed
projects for extended plan development. A series of successive tasks
has been undertaken. The first step involves determination, in further
detail and specifically related to the basin's natural setting, of
surface-water and related requirements for the natural resource complex,
including fishes, wildlife, forests, and recreation; and socio-economic
resource uses, including flood control, urban and industrial develop-
ment, mineral extraction, transportation, and agriculture. Secondly,
hydrologic characteristics of the basin are analyzed for present and
proposed conditions in terms of identified resource requirements. The
above-derived information is then assimilated with environmental base
data developed during the first study, considering constraints posed by
the natural setting and overriding use requirements for flood control.
Management options and present and potential conflicts are identified,
decisions made concerning optimum use, and management needs specified
for such use in so far as possible. Through integration of require-
ments for individual management units and minimization of mutual con-
flicts, a management plan for the basin as a whole is then developed
to the extent allowed by data availability, detailing management pro-
cedures and structural needs. Because of the overriding requirement
of floodway use and improvement, a number of specific goals were set
for the management plan to be developed:
1) maintenance of cross-sectional area of the floodway;
2) increase over present floodway capacity;
12
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3) provision for 1) and 2) in such a way that as much
desirable habitat is preserved as possible;
4) provision for land use that is compatible with flood
control and desirable habitat;
5) maximum utilization of river energy and materials.
Attainment of these goals would provide for accommodation of flood flows
as well as conservation of the natural resources. Maintaining storage
area involves reduction of floodbasin siltatIon,which is presently also
a primary threat to the overflow swamp habitat. Increasing flow capa-
city through utilization of river energy and materials in channel
development would greatly reduce the need for massive dredging and spoil
disposal.
13
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II
CONCLUSIONS AND RECOMMENDATIONS
1. Use of the Atchafalaya Basin in its present form as a
floodway and associated restriction of the functional floodp lain have
increased flux rates of riverborne materials (including water, sedi-
ment! and nutrients) and have magnified water-level variation, con-
tributing further to an increased energy level per unit area The
net result has been enrichment of the ecosystem and acce erated
succession to a more terrestrial environment. Bot*/e^u™n
counter to the need to preserve the basin's renewable resource
values based on its aquatic habitats and to prolong useful life of
the Atchafalaya Basin Floodway.
2. The principal common requirement for Preserving both the
flood-control and renewable-resource values of the floodway is to
minimize sedimentation in backwater areas. ^"S^"^.^
should therefore, be aimed at confinement of Main Channel flows and
reRSaiion of water input into the overflow swamps in accordance with
requirements for maintaining necessary stage variation, water movement,
and water quality.
Examination of the food habits of many fishes, amphibians,
may serve as' Tides for surface-water regulation. A further reason
for regulation of water levels is the need for sufficient dewatering
in ordef to allow aerobic decomposition of detrital matter collected on
the swamp floor.
4 Present annual variation of water levels should be maintained
as much as possible in view of its role in determining plant community
distribution and fish and crawfish production. Maximum and minimum
stages in s^me management units should be reduced to enhance environ-
mental quality.
5. Banks along the Main Channel and major
on iSets
^
lion should be aimed at controlling distributary channels rather than
inflow from distributary channels into individual ^-basins. With
K v notification along distributary channels, such a strategy will
allow a larger pro^ortfon of wate/L enter individual sub-basins
though overbank flow as opposed to channel flow, thus minimizing
14
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backwater sedimentation, and will maintain unrestricted access for
sports and commercial fisheries, and recreation purposes.
6. Total regulation of water inflow and outflow into and from
backwater areas minimizes river water diversion requirements because
precipitation surplus can be effectively utilized. Such regulation
furthermore allows necessary dewatering through evapotranspiration in
those cases where river stage is otherwise a constraint.
7. Hydraulic geometry of the Main Channel suggests that the
proposed Center Channel dimensions, particularly width, exceed those
required by the present regime of Atchafalaya River discharge and
load and would move the channel away from the most probable equilibrium
profile. Therefore, it is recommended that enlargement of the bankfull
channel cross section be limited to 7,400 m2 (80,000 ft2), with spoil
deposited equally along both sides of the channel to achieve maximum
flow confinement.
8. Analysis of management-unit hydrographs for proposed Center
Channel conditions suggests that substantial water-level reductions,
up to 1.5 meters (m), or 5 feet (ft), in Buffalo Cove during the spring,
will occur if the project is implemented without additional structural
provisions.
9. Since most probable equilibrium conditions of the Main
Channel profile suggest a future rise in mean river-stage at Morgan
City, since deep-water access to Morgan City should be divorced from
the main river channel and its associated deltaic sedimentation, and
since eastward diversion of water from the Lower Atchafalaya River is
detrimental to the quality of the human environment of the Morgan
City - Verret area and to quality of the Terrebonne marshes and bays,
it is recommended that serious consideration be given to making Wax
Lake Outlet the principal channel.
10. Many of the present regional problems arise from conflict-
ing surface-water requirements since protective and exploitative
uses of the Atchafalaya Basin's resources have become geographically
intertwined in a pattern that disregards constraints placed by both
the natural and human environments. Therefore, needs for land-use
management are intricately connected with those for surface-water
management.
11. To ensure compatability between land use and use of the
Atchafalaya Basin as a floodway, the Atchafalaya Basin Floodway
should be managed for protective uses to the greatest extent possible.
12. Pluvial swamps on both sides of the floodway should be
managed for protective uses since they constitute high quality habitats
for fish and wildlife, have high recreational value, function as
15
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storage basins essential to present developed areas, and are a po-
tential alternate route for flood diversion when useful life of the
present floodway is ended.
13 A buffer zone, much of which may be used for silviculture,
water regeneration, and aquaculture, should separate present developed
areas from the pluvial and fluvial swamps in order to minimize detri-
mental impact from surface runoff.
14. Complexity of processes in the coastal area below Morgan
City and uncertainty as to causes for present marsh deterioration
prevent detailed management recommendations and require further study,
16
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Ill
REQUIREMENTS OF THE SOCIO-ECONOMIC COMPLEX
, ~- *"-«"«.oc i;««i oe reacned. This chapter
w?tMn S aPterS/eal W±th the needs as ^Pacifically as
Flood Control
The leveed floodway in the Atchafalaya Basin is an integral
combined in the Lower Atchafalaya Basin Floodway. The flood design
? "e nOt Presently met. Excessive
Duri»«Ma>" ""this neoessltated use o th
the
«tifi s^"ted from the over-
artificial levees, u is actually the case in the upper
There the overbank area to the vest is synonymous with the West
17
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PtchofoloyQ Basin. La
FLOOD CONTROL
_ HWPOKO
CCNTfR CHANNEL •'
Figure 3-1.
Flood control aspects of Atchafalaya Basin. Map shows
diversion of water into floodway for design flood and
proposed dredging of Main Channel. Cross sections
relation of natural and artificial levees to overbank areas.
18
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Atchafalaya Floodway; the area to the east coincides with the Morganza
Floodway. In the lower diagram, conditions are shown as they generally
pertain to the middle floodway from Interstate Highway 10 to Morgan
City. Here the channel is separated from the overbank area only by
natural levees and spoil deposits. In the downstream direction, banks
are increasingly overtopped during flood stages. At all stages, river
water diverts into the overbank area through four major distributary
channels before being routed back into the channel at the lower end of
the floodway.
Cross-sectional area is inadequate predominately in the middle
floodway, the lower Atchafalaya Basin Floodway, for a number of
reasons. An overall design cross section has never been attained
because of settlement of the guide levees resulting from poor founda-
tion conditions.8 This reduces the level to which the floodflow line
can be raised. Cross-sectional dimension of the. overbank area has
been significantly reduced as a result of sedimentation. This is
inherent to the presence of a major, unconfincd river attempting to
build a flood plain. Construction of the floodway actually enhanced
this process as it raised the annual level of overflow and limited the
area of sediment distribution through confinement of the overbank area.
A second reason for rapid siltation of the overbank area is the
diversion of water from the Main Channel into the flood basins to
either side through the East and West Freshwater Distribution and
Access Channels (Figure 3-1). Improvement of the Main Channel for
flood control had been attempted until 1967 by dredging and closure of
distributaries. As a result, aided by spoil deposition on the channel
banks, annual flow from the Main Channel into adjacent flood basins
has become increasingly dependent on the four remaining distributaries
mentioned above. These channels permit 20 to 30 percent of Atchafalaya
River discharge to enter the overbank area at high velocities carrying
large volumes of sediment. Much of this sediment is filtered out in
the backswamp areas prior to the return of water to the Main Channel
at the lower end of the floodway. In addition, siltation of the
distributaries occurs, necessitating annual maintenance and spoil
deposition averaging 720,000 m3 (940,000 yd3).9
The contribution of the diversion channels to overbank siltation
appears also substantiated when comparing changes along the west and
*»K. L. Hebert, The Flood Control Capabilities of the Atchafalaya
Basin.Floodway (Louisiana Water Resources Research Institute, Louisiana
State University, 1967), 88 p.
9u. S. Army Corps of Engineers, Preliminary Draft Environmental
Statement. Atchafalaya Basin Floodway,'Louisiana (New Orleans District,
New Orleans, Louisiana," 1974) .
19
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east sides of the Main Channel and relative magnitude of flow
diversion to the east and west, respectively. In the previous
report °0 it was shown that succession toward a more terrestrial
River discharge at Simraesport versus 15 percent toward the eastern
part.
Increases In elevation of the overbank area are illustrated in
Figure 3-2 for a number of management units within the middle flood-
way' The graphs show trends of mean elevations as determined from
U s'c E survey ranges for the period 1930 to present. In general,
elevation sCed a/initial rapid I-™--** ££ f^f "8
S srgSPrh1 first
sfe sri-r
^^,^'2=^ "-sff^rss: 53,-
total of I «.5 mil » deposition probably still occurs in the
(1 ft) over the next fifty years.
dredging and spoil deposition.
l°Coastal Environments, Inc., 1974a, op_.cit.
Investigation of the Atchafalaya Basin
-- °f
1952) , 2 volumes.
20
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12
Eio
1
UJ
i
3
BUFFALO COVE
12
2 « S
« ft 6
S iu
1930 1940 1950 1960 1970 1980 1990 2000
Year
COCODRIE SWAMP
BAY
193O 1940 1950 1960 1970 1980 199O 2000
Year
12
Eio
I
UJ
2
2 £
1930 1940 1950 1960 1970 1980 1990 2000
Year
Figure 3-2. Changes in mean elevation for three
management units.
21
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Table 3-1. Average Sediment Balance, 1965 - 1971, for Atchafalaya Basin Floodway.
12
to
ro
1000 tons
percent
percent
entering
Simroesport
in
Sand
19342
100
Silt/Clay
67905
100
100
leaving
Lower Atchafalaya
River
Sand
3698
19
Silt/Clay
42136
62
52
leaving
Wax Lake
Outlet
Sand
1153
6
Silt/Clay
15590
23
19
remaining
Atchafalaya Basin Floodway
Sand
14491
75
Silt/Clay
10179
15
29
12
U. S. Army Corps of Engineers, 1974, op, cit.
-------
Flow-confinement and channel-formation are of major importance
with regard to the rate at which water can be passed through the
floodway. At a given slope, the channel area,with its greater depth
and lesser surface roughness, allows a much greater rate of flow than
does the overbank area. For this reason, efficiency of the upper
floodway is much greater than that of the middle floodway. As was
shown in Figure 3-1, the channel in the upper floodway is confined
by artificial levees. Partly as a result of this confinement and
partly because of channel age, cross-sectional area below bank level
possibly attains approximately 9300 m2 (100,000 ft2) and is compar-
atively stable.13 The artificial levees confine the How at all
discharges, thus helping to maintain a channel cross section that is
larger than would occur under natural conditions. In the middle
floodway, below mile 54, natural levees are less developed despite
spoil deposition; artificial levees are absent, and time has not yet
allowed development of a well-defined and large channel. Below the
point where artificial levees terminate, cross-sectional area in
which channel flow-conditions occur during flood is much lower in
the middle than in the upper floodway, with an inherently lesser
efficiency to convey floods.
To accelerate the process of channel development in the middle
floodway, a dredging program was initiated in 1954 to increase channel
cross section to 9300 m2 (100,000 ft2) below the floodflow line from
mile 54 to the latitude of Wax Lake Outlet, and to 7400 m2 (80,000 ft2)
from there to the Lower Atchafalaya River. In 1968, the so-called
Center Channel had been enlarged to 5600 m2 (60,000 ft2) and 3700 m2
(40,000 ft ), respectively. Subsequently, the program was suspended
for further evaluation before proceeding to dredge the 9300 m2
(100,000 ft2) channel.
Against the above background, the basic flood-control requirement
for the floodway in the upper and middle basin can be stated as
increased floodway carrying capacity. Alternative solutions, such as
modified diversion routes or proportioning of project floodflows, are
not considered in this section, but have been developed by Task Group I
under the Atchafalaya Cooperative Study.14 In turn, increased carrying
capacity requires either the individual or combined increase of
cross-sectional area of the two parts of the basin and an increase of
flow rate. Present plans call for 1) further upgrading of floodway
guide levees to increase the level to which the floodflow line can be
raised, 2) dredging of the Main Channel (Figure 3-1) to 9300 m2
(100,000 ft^) below the project flow line from mile 54.5 to mile 105.0
and 7400 m^ (80,000 ft2) from mile 105.3 to mile 112,3 to provide for
13u. S. Army Corps of Engineers, 1974, op.cit.
14Ibid.
23
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more efficient flow and depressed flow line during a given discharge,
and 3) further confining of the channel through spoil deposition to
limit overbank siltation.1-'
A second set of requirements concerns the lower floodway and
focusses on the Lower Atchafalaya River, Wax Lake Outlet, and
conditions at Morgan City and in the Verret Basin. Wax Lake Outlet
and the Lower Atchafalaya River provide for discharge of floodwaters
from the leveed floodway through the Teche Ridge into Atchafalaya Bay.
During the 1973 flood, water levels attained unexpected elevations of
3 26 m (10.7 ft) mean sea level (MSL) in the Lower Atchafalaya River
at Morgan City and 3.37 m (10.5 ft) MSL in Wax Lake Outlet at
Calumet. Gage records at Verdunville, Morgan City, and Sweet Bay
further indicate that, at that time, the floodflow-line gradient along
the Main Channel increased from 0.000047 above Morgan City to 0.000086
below Morgan City. This condition suggests strongly that the cross-
sectional area of the outlets was insufficient to pass floodwater
through the Teche Ridge at the same rate it was arriving, thus causing
build-up.
The combined cross-sectional area of the two outlets has progres-
sively changed since completion of the Wax Lake Outlet, when its area
amounted to 9200 m2 (99,000 ft2). The shorter/distance to the Gulf
has favored flow through Wax Lake Outlet so that its channel has
increased in size. At the same time, the Lower Atchafalaya River
filled its channel, but at a more rapid rate. The net result was a
decrease in combined cross-sectional area to 8000 mz (85,000 ft*) prior
to the 1973 flood. During the flood the channels scoured considerably;
therefore, after the flood cross-sectional area had increased again to
8600 m2 (92,500 ft2).
Two problems arise which relate to the extreme levels at the lower
end of the floodway. The first is the direct flood threat to Morgan
City. Existing floodwalls protecting the city from flooding along
the Lower Atchafalaya River proved inadequate under 1973 conditions,
and emergency mud boxes had to be erected on top of the walls. The
second problem arises from backwater flooding. During flood conditions,
tributary channels to the Lower Atchafalaya River actually become
distributary channels diverting floodwaters to the east and west. To
the east, the associated water-level rise thereby partially prevents
drainage of the Verret Basin, for which Bayou Boeuf'is the principal
outlet. Since 1957, this condition has been ameliorated through
construction of a levee along the east bank of Bayou Shaffer and the
Lower Atchafalaya River from Morgan City to Avoca Island Cutoff,
placing the diversion point further downstream, where stages are lower.
However, water still is diverted through Avoca Island Cutoff into
Bayous Chene, Boeuf, and Black. When Atchafalaya River flood stages
15Ibid.
24
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are associated with heavy rainfall, as occurred in 1973, this condition
results in serious backwater flooding, affecting Morgan City as well M
many smaller communities along the low alluvial ridges. 2nd set up
of coastal water may further aggravate this situation.
r*n*f re1uirement» then, is to ensure sufficient
£«,«?.-£ Si, SI?*8 ""^S floodwater from the enclosed floodway
through the Teche Ridge toward the Gulf. This requirement becomes even '
a mor^f^ W^n C°nSiderin* that t^ fi^t objective was to provide
a more efficient center channel and, consequently, a more rapid
delivery of water to the lower end of the floodway.
and Industrial Development
Areas of urban and industrial land use are defined as "areas of
rt A^ K%T Wlth mUCh °f the land C0vered by structures. "16 Wlthin
%nn Ja,Ba8ln' SUCh 3reaS having P°Pu^tions from 5,000 to
25,000 are mainly restricted to the natural levee ridges of the
Mississippi River, Bayou Teche south to Jeanerette, and Bayou Lafourche
south to Thibodaux. Only along these levee ridges does natural setting
n L3i TJr T f ^f f°r Urban and ^^^ 1** use, namely:
1 adequate freedom from flooding, 2) good foundation conditions,
?dev?ate WatCr °r land transportation routes, and 4) a readily
toaflooJ6 SUPP y °f 8?°d 1uality> fresh surface or ground water. Prior
to floodway construction and increased Atchafalaya River discharges
the above requirements were also met along the upper Atchafalaya River
levees, where the towns of Simmesport and Melville developed, and along
the lesser ridges of Bayous Teche and Black, where Morgan City is the
focal point of urban and industrial development. Changes in setting
in these cases now require major flood protection. Simmesport and
Melville on the margin of the West Atchafalaya Floodway, have been
surrounded by ring levees, and a floodwall separates Morgan City from
r \tchafalaya Riv-. *n addition, deepwater access require-
for Morgan city as a resuit °f t
indurJ ^T" areSS that rema±n' althou8h n°t now under urban or
industrial development, meet the earlier-stated requirements- but are
presently committed to agriculture, especially 8u»r cane Thus, urban
and industrial expansion alone the levee crests is severely constrained"
by agricultural use and settlements, while expansion perpendicular to
siLTf ^ COnS^ned bV the presence of wetlands. Although expat
sion into the wetlands has occurred, notably in the Morgan City area
, u » Anderson, et,al., A Land Use Classification System for
Use with Remote Sensor Data (Washington, D.C.: Geological Survey
Circular, U. S. Geological Survey, 1972)
25
-------
this must be considered extremely undesirable not only from the point
of view of detrimental impact on natural resources, but also because
of other reasons. Swamp soils are comprised predominantly of clays
and are high in organic content so that foundation conditions are poor.
Drainage results in substantial compaction and subsidence, aggravating
the already-present constraints of frequent flooding and necessitating
construction of levees and installation of pumping stations. Filling
in the drained and leveed area with foreign soil materials after
allowing several years for soil compaction is often practiced, but
because of the naturally high water table and poor runoff conditions,
pump drainage remains necessary. Additionally, such protected devel-
opment diminishes floodbasin area and thereby storage capacity, thus
increasing average water levels for periods of excessive runoff.
In view of the constraints on urban and industrial use of the
Atchafalaya Basin, the requirements related to water management (free-
dom from flooding, water transportation, and water supply) should
primarily concern existing development and deal with possible expansion,
preferably in areas where the principal requirements are natural
amenities.
Only the natural levee ridges of the Mississippi River, upper
Bayou Teche, and upper Bayou Lafourche fall into both of the above
categories. Water-management requirements for urban and industrial
development along these ridges and related to the Atchafalaya Basin
primarily concern water quality as affected by local runoff.
Local runoff from the Mississippi River and Bayou Lafourche levee
ridge is directed into the Verret Basin. The Fausse Point Basin col-
lects runoff from the upper Bayou Teche levee ridges. This not only
affects water quality as a major element of the natural resources of
these basins, but also concerns the value of basin water as a fresh-
water supply to adjacent developments. The major surface-water
requirement, then, with regard to industrial and urban development
along the major levee ridges is management of surface-water runoff.
This requirement particularly applies to the Mississippi River area,
where deepwater access permits development of heavy industry. The
size and amount of discharge of Bayous Lafourche and Teche restrict
development along their levee ridges to light industry because of
limitations on waterborne transportation, waste treatment and disposal^
and flow rates of freshwater supply.
Further heavy industrial development in the Morgan City area must
be viewed as highly undesirable unless the constraints of the present
setting are taken into consideration. These include limitations
imposed by rich adjacent wetland and estuarine systems and the limita-
tion of suitable areas regarding freedom from flooding and foundation
conditions. Industrial development has already created a demand for
additional dredging and spoil deposition through wetlands, as seen by
the pending enlargement of the Chene, Boeuf, and Black Waterway. Such
26
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construction may, in turn, lead to further industrial development in
highly vulnerable areas and associated urban expansion. With higher
grounds along major waterways considered prime industrial sites
urban development tends to expand laterally into wetlands, rather
than vertically, with known detrimental results to both natural
resources and the urban environment.
Water-management requirements with regard to existing develop-
ment in the Morgan City area concern primarily flood protection and
navigation as described in the previous section dealing with flood
control. A flood-protection requirement has developed largely as
a result of flood routing, high Lower Atchafalaya River stages, and
related obstruction of drainage from the Verret Basin. Proposed
modifications of the Atchafalaya Floodway system do not change this
requirement. Rather, the magnitude of needed protection is likely
to increase. Center Channel construction as presently proposed
would deliver floodwaters at the lower end of the floodway and Morgan
u V*Vn lncreased rate for which no provisions are planned below
the Teche ridge.
Even more important is development of the Atchafalaya Delta, which
will displace the river mouth seaward. As a result of this, Morgan
City is displaced, relatively speaking, landward so that average
river stages will increase. High subsidence rates in the area are
already contributing to this trend.
Essentially, additional flood protection can be provided through
two alternative or combined approaches dealing with the symptoms and
the cause of the problem, respectively. The first requires a wall and
levee system of greater than present height and extended to include
the developed areas along Bayou Boeuf and the area facing Lake
Palourde. The second requires modification of the present flood con-
trol system in order to bring about reduction of stages along the Lower
Atchafalaya River, of eastward diversion from that river into Bayou
Cnene, and of extension of the Lower Atchafalaya River.
Water-management requirements regarding navigation in the Morgan
City area concern primarily deepwater access to the Gulf of Mexico
For this access, industries in the area rely on the Lower Atchafalaya
River and a dredged channel across Atchafalaya Bay. Maintaining a
sufficiently deep channel has become an ever-growing problem as a
result of sedimentation in the shallow bay. With fifty percent of the
Atchafalaya River sediment load discharged into the bay from the Lower
Atchafalaya River, a marine delta is rapidly emerging. The area of
sediment deposition extends from the river mouth seaward beyond the
Point au Per reef, thus totally enveloping the present navigation
channel. Maintaining a channel through an actively prograding delta
is possible only, if at all, through great moneta and energ£
diture. The difficulties involved in maintaining such a channel are
27
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inherent to the process of delta building, with highest sedimentation
rates occurring at the channel mouth, where flow is no longer confined
and velocities decrease. Any attempt to circumvent the sedimentation
process by extending the channel only displaces the problem seaward,
at least as long as water depth over the area of sedimentation is
less than that-required for navigation. In the present case, dredging
would not solve the problem unless it was continued to a distance of
40 miles offshore,where depth presently is 30 feet. Clearly, the
navigational requirement is to separate deepwater access from the
active river mouth.
An additional navigation requirement is the maintenance of inland
waterways. Presently, navigation routes are provided by the Atchafalaya
River and the two routes of the Intracoastal Waterway, an east-west
route through the coastal marshes and a north-south route connecting
Korean City with the Mississippi River at Port Allen. The latter route
utilizes the eastern guide levee borrow pit as far as the settlement
of Sorrel,where a lock provides for crossing the guide levee.
The third management requirement for the Morgan City area concerns
maintenance of water supply and quality. Fresh, ground-water supplies
in the area are limited and of poor quality. Municipal water is
derived from the Atchafalaya River and, in case of emergency, from Lake
Palourde. Whereas quality control of the first source lies mostly
beyond the Atchafalaya Basin, control over the second source is
entirely dependent on management of surface-water runoff into the Verret
Basin as a whole.
Agriculture and Rural Settlement
Historically, agricultural development and associated rural
settlement have been concentrated along the major natural levee ridges,
with relative freedom from flooding and well-drained, fertile, and
easily workable soil. Settlement related to wetland-based industries,
such as fishing and trapping,also concentrated on natural levee ridges,
usually the lesser ones associated with small streams within the swamps.
This pattern has experienced some significant modification as a result
of floodway construction.
The West Atchafalaya Floodway and Morganza Floodway, although
part of the Atchafalaya Floodway, are well protected from annual
Atchafalaya River flooding by artificial levees. Never having been
used since construction and with only simple flowage easement pertain-
ine the West Atchafalaya Floodway has seen widespread agricultural
development and settlement, further contributing to an illusionary
sense of security. Some twelve communities are existent; a 1972
census by the U.S.C.E. showed 3,524 persons residing in the floodway,
874 homes being permanent structures. Agricultural development has
also followed in the Morganza Floodway, but here comprehensive
28
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easements ban all buildings for human habitation from the floodway.
Si th8aS?a ^r 1S the f±rSt t0 receive urgency diversion
from the Mississippi River and has been used in the past.
8etM^!hJn ^ L°Wef Atchafalaya B*sin Floodway, agriculture and
settlement were mostly abandoned as Atchafalaya River discharge
increased up until 1965. Settlements became limited mainly to the
previously existing communities of Butte La Rose and Safalaya
both on the old Atchafalaya River natural levee ridge . Maintenance
of those settlements was possible through extension of tS Atchara-
of^hf W6^ rr/? ^^ the S6ttled a*6aS became an extension
onn^M Atchafalaya Floodway, with flood threats limited to
conditions of backwater flooding and use of the latter floodway.
flnnHDiSPla 3nd ±n the upper Verret «asin north of
Highway 190. Extensive agricultural development is also present in
the area wedged between the Atchafalaya and Mississippi Rivers north
of the Morganza Floodway, called the Point Coupee Loop, which is
surrounded entirely by artificial levees. Smaller-scaie development
and rural settlement has occurred on narrow-levee ridges, such as
r±8JTUf laCk' a?d °n th°Se transecting the Verret Basin and
related to former, minor distributaries. Barely above the level of
adjacent swamps, the lands and settlements of the latter type are
highly vulnerable to flooding as a result of two processes^ backwater
flooding and, ironically, drainage improvement. backwater
f«00 Backwf7f r f ^ing of the Verret Basin was discussed earlier
(see page 27) with regard to contributive factors. In the Fausse
Point Basin, backwater flooding relates to insufficiency of the
29
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Charenton Canal as a drainage outlet, in particular during the periods of
wind setup in the coastal bays.
Drainage improvement of natural levee ridges tends to have two
effects. It makes existing agricultural areas more desirable for
urban and industrial development and opens up new marginal areas for
agriculture along the levee-swamp interface. As a result of both,
agricultural development tends to expand or shift toward that interface
where marginal conditions again require drainage improvement. Such
improvements will accelerate runoff from the natural levee areas,
increasing rates at which water is contributed to the swamp basins,
which have an inherently poor drainage network. Consequently, average
water levels are raised. In addition, storage capacity of the swamp
is reduced by the reclamation of its margins and has the same effect.
Aeainst the above background, water-management requirements can
be considered. As in the case of urban and industrial development
these concern primarily flood protection and water quality, with the
former preferably limited to presently developed areas and potential
areas that are naturally suitable. With regard to flood Flection,
Se major requirement appears to be minimization of backwater flooding
relate^ to A?chafalaya discharges. This demands ^ the greatest ex-
tent possible separation of the Verret Watershed from the Lower
Atchalalaya River. In combination, adequate flood protection may re-
quire low flood dikes unless major channelization of swamp streams
2s undertaken to allow rapid removal from the basin. The latter must
be considered in direct conflict with the natural resource base. A
forced drainage district has been planned along Bayou Black in Terrebonne
Parish.
Runoff presents a water quality problem not only with respect to
the natural environment, but also in regard to the freshwater supply
represented by waters of the basin. Management for quality control of
runoff into the swamps from the settled and agricultural lands within
the floodway north of U. S. Highway 190 and flow from the major levee
ridges marginal to the Verret and Fausse Point Basins are a second
major requirement.
Proposed enlargement of the Main Channel of the Lower Atchafalaya
Basin Floodway and concomittant lowering of flood stages may well in-
5£ agricultural development into that area, even though most lands
Ire only marginally suited for this and can be developed only at great
Sense! Yet, this remains feasible even to the extent of settlement.
Seventy-five percent of the lands are in private ownership, and only
simple'flowage easements were acquired by the U.S.C.E. over small,
scattered areas which were not subject to frequent overflow as of 1928.
From this appears a third requirement, that of ensuring compatibility
between land use and function of the floodway.
30
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Oil and Gas
Exploration for oil and gas is among the human undertakings that
have brought about major environmental change in the Atchafalaya
Basin. In the absence of trafficable ground, access to drilling
sites is invariably obtained by dredging a canal from the nearest
waterway. Successful drilling has often been followed by pipeline
installation, requiring additional canals. As a result, a dense and
seemingly random network of canals and spoil banks has been superim-
posed on topography and hydrography of both the swamps and marshes.1?
Their effect on the natural resource base has never been fully
assessed,though numerous examples of detrimental change can be
*nHnJ «??; ^J8? ,include excessive sedimentation in backwater areas
and infilling of lakes, obstruction to water movement resulting in
water quality problems, and changes in hydroperiod toward insufficient
dewatering or excessive drainage.
One set of requirements for surface-water management relates
directly to the above impacts and can be summarized as the integration
of present and future canals into the natural system. Even though
drilling success has yielded increasingly to failure in the past five
years, indicating only limited reserves, it must be assumed that
drilling will continue for some time. This means that unless more
costly means of exploration,such as directional drilling,are utilized,
canal dredging will continue in order to provide access and pipe-
^J0?6!* Whlle P°licies established by the Louisiana Wildlife
and Fisheries Commission have been in effect since 1970 concerning
closure of canals at intersections with major sediment-carrying channels
and provision of gaps in spoil banks, the principle of a straight line
being the shortest distance between two points remains applied to
selection of canal locations. In this regard, a requirement, clearly,
is the selection of routes that adhere to the hydrographic grain of
sub-basins to be traversed. On a larger scale, this may become
increasingly important where major lines connecting offshore fields
and onshore markets must cross the Atchafalaya Basin.
A second requirement relates to possible assets of the canals.
As a result of sedimentation, many lakes and streams have decreased in
size and depth to the extent that they no longer serve as a fish
habitat during the late summer and early fall,when water levels are
low water temperatures are high, and oxygen concentrations decrease
significantly. Because of depth and contained volume of water, canals
pppear less affected by these constraints and are known to provide
good sports fishing. Because low water conditions isolate many of the
ofnSLfntY^fTnP 8ySt?m ^ S reSUU °f SP011 banks> integration
of present and future canals into the swamp system with regard to both
17coastal Environments, Inc., 1974a, op_.cit.
31
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access and circulation is seen as a requirement to offset habitat
losses through sedimentation and especially through lowering of water
levels as a result of Center Channel construction.
A third requirement concerns access to drilling sites and oil
field installations. Weight of this requirement with regard to future
drilling and associated movement of equipment can be assessed only on
the basis of known and possible reserves. This cannot be evaluated
here except to point out the decline in productive new wells relative
to the number of wells drilled. There will remain however, the need
for maintenance of wells and other oil field installations even if no
additional wells are drilled. Yet, no systematic evaluation has been
made with regard to boat traffic related to mineral industry activi-
ties as to numbers, draft, and routes used in present operations.
Therefore, no specific requirements can be stated concerning navigation
related to the mineral industry.
Recreation
Recreation in the Atchafalaya Basin hinges on the relatively
unspoiled wilderness characteristics prevalent in the area. The basic
requirement, then, for maintenance of the recreational attractiveness
of the basin is the preservation of the existing natural amenities.
Sajor forms of recreation in the basin include hunting, fishing,
crawfishing, pleasure boating (including canoeing), picnicking, camping,
and nature study (including birdwatching). Because of the wet charac-
ter of the basin, most recreation is water-oriented or water-related.
Soort fishing is probably the most popular recreational activity.
There are few weekends in the year when a fishing tournament or rodeo
is not held in some area of the basin. This area is nationally known
among enthusiastic fishermen for its ability to produce great numbers
of large-mouth bass. Species like bluegill, crappie, warmouth red-ear,
and catfish are also taken in good numbers by both boat and bank
fishermen.
The popularity of fishing in the basin attests to the abundance
of sport fishes in these waters. Large standing crops of fishes can
be attributed to the immense area of aquatic habitat and to the annual
overflow of Atchafalaya River water into backswamp areas,which stimu-
lates fish reproduction and enhances overall productivity. Preserva-
tion of these characteristics is essential for maintenance of the
presently high value of the recreational fishing resource.
Crawfishing is a pastime which is almost unique to Louisiana. The
pursuit of "mudbugs" is often the basis for family outings during the
spring season when many avid crawfish-seekers may be seen lifting set
nets (similar to crab nets) hopefully full of the tasty crustaceans.
32
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Crawfish are sought throughout southern Louisiana in swamps, marshes,
roadside canals, and in almost any place where there is shallow water
with much aquatic vegetation. That portion of the West Atchafalaya
Floodway along U. S. Highway 71 is a favorite recreational crawfishing
area. The borrow pit canals inside the floodway protection levees
and the large swamp area of the Grosse Tete-Verret-Palourde Basin
east of the floodway are also heavily used.
The recreational crawfish harvest is quite large. Soileau,
et al. estimated the 1971-1972 sport catch at 1,117,000 pounds, and
their study area included only the floodway between U. S. Highways 190
and 90.10 The sport crawfish catch throughout the natural Atchafalaya
Basin could be twice this amount, and in some years may rival the
commercial catch in size.
The requirement for maintaining the value of recreational craw-
fishing in the Atchafalaya Basin is the preservation of existing
aquatic habitat conditions and continuation of natural water-level
fluctuation in backswamp areas. The life cycle of crawfish is
intimately related to fluctuating water levels and is further described
in another section of this report (see -Requirements for Crawfish
Production).
Hunting (see sections of report on Game Animals and Waterfowl)
for such game as deer, rabbits, squirrels, and ducks is a major
recreational activity in the basin. Recreational hunting depends on
availability and abundance of game which, in turn, requires approp-
riate habitat types. Thus, habitat preservation is a basic requirement
for hunting recreation.
Most land in the basin is privately owned and is leased by owners
to private hunting clubs. As a result, many would-be hunters who
cannot afford to join hunting clubs or who hunt too infrequently for
joining a hunting club to be of value have no place to hunt. Establish-
ment of state-owned public hunting grounds in the basin would greatly
benefit this group.
Other types of recreation in the Atchafalaya Basin, such as pleas-
ure boating, picnicking, camping, and nature study, are founded on
the scenic and wilderness qualities of the swamp forests. Cypress
trees with their buttressed trunks and lacy foliage, often heavily
draped with Spanish moss, contribute greatly to the beauty of the swamp.
Possibilities of observing wildlife, such as herons, raccoons, and an
occasional alligator, add to the attractiveness of swamps. Wilderness
and scenic qualities are the main attractions of the basin to canoe-
ists, picnickers, and many campers. Many hunters and fishermen
18Lawrence D. Soileau, et al., Atchafalaya Basin Usage Stud^-
Interiin Report (Louisiana Wild Life and Fisheries "
Orleans, Louisiana, 1973) 44 p.
33
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maintain more or less permanent camps built on small ridges or rafts
from which they base their operations.
Opportunities for both formal and informal nature studies are
abundant in the basin. The life history and ecology of many of the
basin's inhabitants have never been accurately described. Many fea-
tures of the lives of invertebrates, fishes, amphibians, reptiles,
birds, and mammals await elucidation by students of natural history.
Recreation in the Atchafalaya Basin, then, has its foundation
on the existing natural wilderness and fish and wildlife resources.
This requirement for maintaining recreational values is the preserva-
tion of the existing resources upon which recreation is based.
34
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IV
FORESTS OF THE ATCHAFALAYA BASIN
General Nature of the Atchafalaya Basin
The forests, marshes, lakes, estuaries, bayous, rivers, pas-
tures, croplands, and towns which cover the area of the Atchafalaya
Basin can all be viewed collectively as a single ecosystem. In this
ecosystem, there are thousands of various kinds of organisms with many
thousands of interactions or relationships among them. All of these
organisms have particular requirements for space and other resources.
Due to the widely varied preference in space and other resource needs,
few organisms are distributed uniformly throughout a complex ecosystem,
but are instead discontinuously distributed in places where these re-
quirements are met. This sorting-out process leads to formation of
associations of plants and animals which have related space and other
resource needs. Fortunately, not all of these organisms are of equal
importance in determining the overall character of the ecosystem so
that we can infer much about its dynamics from considerations of a
smaller group of abundant life forms.
Plant communities of the Atchafalaya Basin are of basic impor-
tance in the ecosystems of which they are components. The vegetation
uses the energy of the sun in its production of plant matter, which is
the energy base of all other elements of the ecosystem. The architec-
ture or spatial structure of the ecosystem is largely determined by
the growth forms of the plant species that dominate a given area. Vege-
tative types have an important effect on the water budget of an area
through processes such as interception of rainfall, evapo transpira-
tion, and flow retardance.
There is very little known of a detailed or quantitative nature
an ecosystem comparable to the Atchafalaya Basin. For this reason
we can make only certain general inferences based on observation of
processes that take place in such a system. In the following para-
graphs, a broad sketch of the general nature of the Atchafalaya Basin
will be presented.
Most of the higher and better-drained lands of the Atchafalaya
Basin that are not subject to frequent inundation have been cleared
and are under use for agricultural or other human purposes. The re-
maining lands are for the most part forested by many different types
of tree associations. Except for black willow, there have been no
virgin tree stands in the entire area since the last phase of the in-
dustrial cypress lumbering era, which drew to a close during the 1930
to 1940 decade. J-y Many of the native hardwood stands on higher grounds
Mancil, An Historical Geography of Industrie yp^gg
Lumbering in Louisiana (Ph.D. Dissertation, De?aVtment of Geography"
and Anthropology, Louisiana State University, 2 volumes 1972)
35
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had been taken prior to that time. Few accurate descriptions exist
as to the nature of these original stands of trees or of their asso-
ciated organisms; although this is of interest to the natural histor-
ian, it is largely irrelevant to the forest conditions of the Atcha-
falaya Basin today.
The forest communities of the basin range from bottomland hard-
woods to cypress-tupelo. Each community type will be considered in
some detail in later sections, but it is important to point out that
all of them have certain basic similarities. The major tree species
are deciduous, for instance, and this fact gives a seasonal pulsation
to numerous processes over the whole area. Each tree species has its
own distinct form of growth, yet all of them have analogous characters
leading to a generally similar series of levels of stratification.
Each has a soil zone which is densely root-penetrated. Above the soil
is the zone of understory vegetation and tree boles. While the forests
are flooded, there is an aquatic zone over the soil. All tree communi-
ties have an uppermost canopy zone of branches and leaves. There is
a continual cycling of material within and between these strata.
Branches, bark, and leaves are continually shed from the canopy and
fall to the forest floor. Lichens on branches and bark may be impor-
tant sources of fixed nitrogen. Similarly, bark is continually shed
from tree boles, and materials are shed from the understory elements
onto the soil surface. Numerous organisms find habitat and niche in
the various strata and add their part to the flow of materials. Birds,
insects, mammals, amphibians, and other organisms which exist in the
canopy layer also provide a continual stream of materials in the form
of excreta, molted exoskeletons, and various other substances. These
are mingled with the plant debris littering the forest floor and form
a substrate for a wide range of decomposer and detrital-feeding organ-
isms. Additional nitrogen may be fixed in the process of decomposi-
tion by certain fungi.2" Animals of many kinds on the forest floor
are important agents in the transformation of this debris through ac-
tivities such as burrowing, digging for food, or otherwise moving the
material.
Forest communities of the Atchafalaya Basin exhibit various forms
of stratification depending on community type. The cypress-tupelo
community, for instance, is often made up of a few age classes of
trees since conditions for germination are best during occasional dry
years. The even-aged stands, then, may have a relatively well-defined
stratification of two or three distinct generations of trees. In
the cypress-tupelo community, lianas are largely absent, which is a
marked contrast to the architecture of this forest type as compared
to better-drained sites. The most abundant epiphytes in the canopy
zone are lichens of which a variety of fruticose forms are very numer-
ous on the higher branches. Spanish moss is a common epiphyte,
20B. W. Cornaby and J. B. Waide,"Nitrogen Fixation in Decaying
Chestnut Logs '{Plant, and. Soil, Volume 39, 1973).
36
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especially in the vicinity of openings in the canopy such as lakeshore
situations. On the boles of the trees, encrusting lichens are numer-
ous and mosses are common. In crooks of the bole, mosses are es-
pecially prominent along with the resurrection fern (Polypodium poly-
podioides). Numerous fungi occur as well both on the canopy branches
and the bole. A notable example is the pecky cypress fungus (Stereum
sp.)»which can extensively consume the woody tissue of baldcypress.
Many hollow tree trunks are created by fungi and other agents, and
these hollows must be regarded as important architectural elements of
the system because of the habitat they provide for various organisms.
There is a complex association of wood-boring organisms, many of which
are prey of other species, such as the several kinds of woodpeckers
which bore into the wood, thereby creating other habitat opportunities
for many other species.
Another aspect of the ecosystem can be termed its temporal struc-
ture, which refers to its sequence of regular events through a typical
year. The river flood cycle is a major element of the temporal struc-
ture. The yearly cycles of leaf fall, flowering, fruiting, and germ-
ination, which vary widely among the different plant species, are all
part of the overall temporal structure. The life cycles of animals,
which are tremendously varied, are important time-structure elements as
well.
The Atchafalaya Floodway represents a restricted artificial flood
plain of the Mississippi - Red River system. Prior to artificial con-
trol, these rivers spread their floodwaters over a large area of south-
ern Louisiana. Because the area of flooding was large, the rates of
material and energy flux at most sites were relatively small. As the
artificial levees along the Mississippi River were built, the movement
of floodwater became increasingly restricted and eventually was dimin-
ished to the small area of batture lands lying between the levees and
to the Atchafalaya River basin. With the creation of the Atchafalaya
Floodway, the area over which floodwater could spread was even further
restricted.
As a consequence of the diminished area of land over which flood-
waters can spread, the sedimentation rates have risen, as has the flux
rate of all other materials carried by the river system. The artifi-
cially achieved shrinkage of the floodplain area has impressed its im-
pact on the ecosystem of the Atchafalaya Floodway area primarily
through increased rates of flux of riverborne materials entering the
area.
Water is the most abundant material carried into the floodway
and, due to the restrictions on its spread caused by the protection
levees, this water exhibits an amplified stage variation in comparison
to pre-floodway conditions. This amplification of flood hydrographs
has been responsible for much habitat change in the floodway.
37
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It is important to consider, however, the other materials moving
through the river system in addition to the water. Suspended solids
are second in amount to water in the materials transported into the
floodway. Bryan et al. found an average concentration of about 0.4
grams per liter (g7l) in mainstern Atchafalaya water at mile 77-3.-*1
This is in agreement with data (Figure 4-1) presented by the U.S.
Army Corps of Engineers in its environmental impact statement.zz From
this, it appears that the amount of suspended matter being carried
into the system is declining. This is probably due to increasing num-
bers of reservoirs throughout the upstream segments of the Mississippi-
Red River drainage basins.
The third most abundant material moving down the river is the
dissolved solid matter. According to the U. S. Army Corps of Engin-
eers 23 the dissolved solids over the five-year period 1968 - 1973
were generally in the range of 190 - 240 milligrams per liter (mg/1).
In this case, there are not sufficient data to show if there is a
long-term trend in dissolved solids concentration. This dissolved
material includes a wide range of substances, including many impor-
tant nutrients. The reduced surface area of the artificial flood
plain again means a higher flux rate per unit area than that which
existed before human modification. This has, in effect, enriched the
ecosystem of the floodway with important vital materials.
The fourth most abundant class of materials in transport in
the water is the organic matter. Bryan et, aJL. report an average of
7.9 mg/1 of organic carbon at mile 77.3, which means that total organ-
ic matter is about two times that value, or roughly 16 mg/1. Again,
flux rate of this material, which represents both food and potential
nutrient matter in the floodway ecosystem, is greater now than before
the floodway existed.
Not only have material fluxes increased due to artificial con-
finement of floodwaters, but the energy of the moving water is also
greater per unit area than it would be without the floodway. Much of
this energy contributes to biological processes by various means.
This is the basis of the well-known fact that flowing water systems
are more productive than static water systems. This fact seems to
arise primarily through the higher circulation rates of vital mater-
ials, such as nutrients and dissolved gases, in flowing water. Con-
struction of the floodway, then, must have led to increased produc-
tivity for the several reasons given above. Such increase augmented
2lBryan,et al. t!974, op_. cit.
22U. S. Army Corps of Engineers, 1974, pp. cit
23Ibid.
2*Bryan,et al., 1974, 0£. cit.
38
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E
§"1000
2
4>*
2 0
ig
<
-------
an already-high productivity, which has as its primary reason
shortness of the food chain: detritus - crawfish - large
predators.
With regard to the area of the Atchafalaya Basin which is out-
side the floodway, much the opposite kinds of conditions have come to
prevail since these lands became artificially separated from the river
flood plain. The lands at lower elevations now are flooded largely
from rainwater falling directly upon them or entering them from the
agricultural drainage districts or urban developments which occupy
higher ground. Such flooding does not lead to the extreme stage var-
iation characteristic of the floodway. Suspended matter can be high
at certain times in the runoff from the developed areas, but it is
far less than the levels in the highly turbid river waters which for-
merly entered these areas. Dissolved solids may be high, particularly
where argicultural and urban runoff are high; however, total quanti-
ties of these contributions are far less than those in flux through
the river waters of the floodway. Most organic matter is produced
within these systems since they have no important allochthonous con-
tribution, as does the floodway. Water movement through these systems
is not nearly as energetic as in the floodway due to the much lesser
volume of flow.
It is against this background of fundamental conditions that we
must view the Atchafalaya Floodway and isolated swamp ecosystems.
The forests of these areas vary largely in accordance with these con-
ditions, and in the remainder of this discussion, we shall emphasize
the following factors which exert considerable regulating control on
the forest ecosystems.
1) Hvdroperiod. This refers to the duration of flood conditions
at a site. In the floodway, low-lying areas may have prolonged hydro-
periods during an average year. Outside the floodway, isolated swamp
areas are less likely to have long flood duration since they have main-
ly pluvial water sources. The nature of flooding, particularly its
timing, is a primary determinant of tree species distributions.
2) Sedimentation. This refers to the degree or rate of sedi-
ment accumulation at a given site. Understandably, this is quite
different for low-lying sites within the floodway than for those out-
side of it. Sedimentation rates are also a primary, determinant of
tree species distributions.
Conditions in the Bottomland Forests
Most of the bottomland tree species begin to develop leaves
and flower in the period from March to April. For most
species, fruit maturation occurs in the fall, and germination is in
the spring. However, the species following this schedule are largely
40
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those characteristic of the lowest hydroperiod lands. Species which
characterize longer hydroperiod lands often have a different schedule.
Black willow and cottonwood both show a similar reproductive strategy
that differs from the other bottomland hardwoods. Both may begin to
flower relatively early (February - March) and then produce mature
seeds very shortly afterwards (April - July). Both have seeds that
will germinate almost immediately after arrival at a suitable site on
moist mineral soil. The seeds do not remain viable for any appreci-
able length of time in dry conditions, but may remain viable for sev-
eral weeks in water. Red maple has a schedule of early flowering
(February), early seed maturation (March), and germination in early
summer. Baldcypress flowers early (December --January) and produces
ripe seeds later than most trees of the basin (November - December).
Baldcypress seeds apparently germinate best in spring, but since the
swamp is usually flooded at this time, good years for germination are
few and far between. Baldcypress seeds are known to remain viable in
water for extended periods and may germinate over a greater span of
time than most species. Water tupelo develops flowers and fruit si-
multaneously with most other species of the area, but its germination
takes place in mid-summer. The later period of seed germination for
black willow, cottonwood, red maple, and water tupelo obviously is a
favorable adaptation for floodplain species since soils are less likely
to be flooded at this time.
When floodwaters from the river begin to flow through the over-
flow swamp areas, the processes that take place are complex. Ini-
tially, the input of rainfall surplus is high, and the floodwaters are
diluted with this source. By spring, however, transpiration, evapor-
ation, and interception have increased to the point that rainfall sur-
pluses do not exist, and floodwaters are the primary input to continued
flooding.
In the initially flooded swamplands, there is frequently a heavy
organic surface litter left over from the fall leaf abscission and from
all earlier leaf, branch, or trunkfall remains in varying stages of de-
composition. This high biological oxygen demand leads to rapid devel-
opment of an anaerobic soil profile and low oxygen in the water. Even
in such early waters typical of the cooler months of the year, oxygen
may be no more than 3-5 parts per million (ppm). As temperatures
rise and production and respiration both increase, oxygen frequently
declines to still lower values, suggesting that respiration is exceed-
ing production in the water column. In areas of extensive water hya-
cinth mats, there is a high demand from the dead parts of the mat,while
the plant cover greatly interferes with gas exchange between the water
and atmosphere. Such waters become low in oxygen quickly.
Estimates of primary production from swamp systems of the kind
found in the Atchafalaya Basin have not been made. Studies in the
swamp basin above Lac des Allemands, a short distance to the east of
the Atchafalaya Basin, by personnel of the Center for Wetland Resources
have shown that waters of streams draining the swamps have much higher
41
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active chlorophyll a_ concentration than other waters studied in the
coastal zone. Day elt al. stated that this suggests that such swamp
systems are "highly eutrophic."25 The isolated swamps of the Atcha-
falaya Basin are probably comparable in character, whereas the flood-
way swamps are more limited in phytoplankton bioraass due to highly
turbid waters. Diurnal oxygen curves in the Lac des Allemands swamp
waters showed little daily fluctuation, and oxygen was generally low
despite the high phytoplankton biomass. Day et_ al_. described this as
a "strongly heterotrophic aquatic system due to the l|?8e quantities
of dissolved and total organic carbon in the waters."
There are many areas in the Atchafalaya Basin where the high
nutrient flux of the system is evident. Among these are the areas
of prolific and recurrent water hyacinth blooms, which become anoxic
in warmer months. The Buffalo Cove area has been cited as a case of
this type in earlier work. ' In this area, a chronic and recurrent
water hyacinth bloom at times has covered an area of 51.8 square kilo-
meters (km2) or 20 square miles (mi2). Fish kills and kills of craw-
fish that have been taken in traps are problems in such areas.
Coleman reported that soils of the poorly drained swamps
contain mineral pyrite (FeS,), ferrous sulfide (FeS), and vivian-
ite (FeoP9Oo8H90).28 Thus, to some extent, the soil acts as a sink for
iron, sulfur, and phosphorus through the formation of these substances.
From this, it is apparent that phosphorus and iron are not likely lim-
iting. Nitrogen may be the principal limiting element in most Atcha-
falaya Basin systems.
Water hyacinth is a dominant plant in many areas of the basin.
In the Buffalo Cove area, for instance, water hyacinth has in recent
years occupied most of the long hydroperiod habitat, an area of ap-
proximately 51.8 km2 (20 mi2). The lower part of the Upper Belle River
unit is also an area of chronic water hyacinth cover over an even
wider area. In these localities, the water hyacinth cover is virtu-
ally 100% during some years. In the marshes flanking the Atchafalaya
River mouth in western Terrebonne and St. Mary Parishes, extensive
25John W. Day, et al., "Flora and Community Metabolism of Aqua-
tic Systems within the Louisiana Wetlands," in Environmental Assess-
ment of a Louisiana Offshore Oil Port and Appertinent Storage and Pipe-
line' Facilities (Volume 2, Technical Appendix 6) 39 p.
26Ibid.
2?Coastal Environments, Inc., 1974b, op. cit.
28James M. Coleman, "Ecological Changes in a Massive Fresh-Water
Clay Sequence," Gulf Coast Association of Geological Societies, Trans-
actions (Volume 16, 1966).
42
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water hyacinth cover has developed within and replaced freshwater
marshes during recent highwater years.
Areas of chronic water hyacinth cover within the floodway appear
to represent areas of a great amount of river water throughflow. Hya-
cinths respond to flowing water conditions by vigorous growth due to
the constant renewal of root exposure to the water with its nutrient
substances. Rafts of hyacinth are trapped and held in the tree-covered
swamp areas as a result of jamming against tree trunks or understory
vegetation. As these continue in rapid growth, the area of cover may
expand to fill the entire flooded swamp basin. During low water per-
iods, the matted hyacinth may be killed from dessication in areas
which are exposed to drying conditions, but in lower-lying places they
persist throughout the year. As waters rise again in the swamps, the
hyacinths may increase in cover at virtually the same pace as the
spread of flooding.
While mats of hyacinth can develop rapidly in flowing water con-
ditions, it must be mentioned that the growing mat increasingly becomes
a retardant to water flow due to the heavy root systems which dangle
as low as three feet beneath the mats. Energy is dissipated through
friction, turbulence, and bending motion imparted to the roots as water
passes through beneath the mat; consequently, flow speed is reduced.
Timmer and Weldon, among others, have shown a high water loss
for water hyacinth mats, averaging 3.7 times higher than an open water
surface.zy Why this is so is unclear, but it must be related in part
to the stomatal structures described by Penfound and Earle, who report
that their average number, 120 per square-millimeter (mm2), is typical
of other plants, but that their aperture size, 12 microns (v) by 27 y,
is much larger than a typical value for other plants. Thus, the
area of apertural opening is high. For this reason, they conclude
that, ". . . it is evident that the water hyacinth, with a moderate
number of very large, evenly distributed stomata, is well-equipped for
rapid diffusion of gases."30
Another interesting aspect of water loss from floating hyacinth
mats is that it varies according to water flow. Rogers and Davis showed
that transpiration per plant was 175 milliliters (ml) in static water
and 225 ml in flowing water.31 This was measured under controlled con-
ditions using uniform-sized plants. Under natural Conditions, the
29
C. E. Timmer and L. W. Weldon, "Evaporation and Pollution of
Water by Water Hyacinth," Hyacinth Control Journal (Volume 16, 1967).
30W. T. Penfound and T. T. Earle, "The Biology of the Water Hya-
cinth," Ecol. Monogr. (Volume 18, 1948).
31H. H. Rogers and D. E. Davis, "Nutrient Removal by Water Hya-
cinth," Weed Science (Volume 20, 1972).
A3
-------
water loss in flowing water areas could be even greater since Penfound
and Earle observed that in flowing water, hyacinth stands tended to
have larger leaves with greater surface area.32 Since Timmer and
Weldon's estimate of water loss from hyacinth cover is based on static
water measurements, 33 it is likely that flowing water situations, such
as those of the Atchafalaya Floodway, experience even greater water
losses.
The ability of water hyacinth to absorb large quantities of nu-
trients has been noted by several workers. Rogers and Davis noted
that a single plant could absorb between 5.3 and 19.8 milligrams (mg)
of nitrogen (N) per day,3^ depending on the concentration of N in the
nutrient medium. In simulated flowing water systems, they found ab-
sorptions increased to a range of 9.9 - 20.8 mg per plant per day.
In a sewage effluent, they noted absorption of N at a rate of 6.6 mg
per plant per day in static water conditions. Phosphorus(P) was absorbed
at rates ranging from 1.1 - 3.1 mg per plant per day in flowing water.
Shamsuddin showed daily absorption rates of N per plant to be
24 24 and 3.5 ppm in media to which 50, 100, and 250 ppm of N were
applied 'respectively.35 He showed orthophosphate daily absorption
rates per plant to be 0.4, 0.4, and 0.7 ppm in media to which 50, 100,
and 250 ppm of orthophosphate were applied, respectively. The N:P
uptake ratio ranged from 5 - 6 in these experiments, corresponding
to Boyd's estimate36 that water hyacinth plants contain about six
times as much nitrogen as phosphorus.
For these reasons, water hyacinth has been considered on numer-
ous occasions as a potential contributor to wastewater treatment.*'>
58,39 According to Webre,40 an experimental plant of this kind is
under construction at the National Space Technology Laboratories (NSTL)
32Penfound and Earle, 1948, o£. cit.
33Timmer and Weldon, 1948, op. cit.
3*Rogers and Davis, 1972, op. cit.
35Z. H. Shamsuddin, Field and Laboratory Studies of Fertilizer
Runoff and Its Effect on Eutrophication of_ Natural Waters (M.S. Thesis,
DepartminT of Agronomy, Louisiana State University, 1973), 79 p.
36C. E. Boyd, "Vascular Aquatic Plants for Mineral Nutrient Re-
moval from Polluted Waters," Econ. Botany (Volume 24, 1970).
37Ibidt 38Rogers and Davis, 1972, op. cit.
39shamsuddin, 1973, op. cit.
4°G. Webre, "Water Hyacinth - A Disposal Plant," Dixie Magazine
(New Orleans: The Times-Picayune, March 2, 1975).
44
-------
under the direction of B. C. Wolverton. He has noted not only significant
nutrient uptake, but also that pesticides and heavy metals can become
concentrated significantly by hyacinths growing in polluted waters.
The NSTL programs presently project the growth of water hyacinth on
sewage discharge waters with subsequent fermentation of the hyacinth
biomass to yield methane gas and a composted fertilizer material.
The implications of Wolverton's evidence of pesticide and heavy
metal buildup in water hyacinths suggest that some attention should be
paid to this process in the widespread blooms of hyacinth that exist
in nature in the Atchafalaya Basin. To date, there are no useful chem-
ical studies of this plant in its natural circumstances. Its ability
to accumulate nutrient substances from waters flowing through the
Atchafalaya Basin accounts in large part for its widespread occurrence
and rapid growth rate. This ability may likewise account for its ex-
cessive production in areas of massive cover,which experience oxygen
depletion mortalities of aquatic fauna.
Lynch e£ aJL. first reported that oxygen concentration beneath
closed water hyacinth mats is very low.41 Penfound and Earle reported
values beneath closed mats with about 10.16 centimeters (cm), or 4
inches (in.), of bottom litter accumulation were less than 0.1 ppm,
and beneath closed mats without significant litter accumulation, the
values were about 0.5 ppm.*2 They also noted that in semi-closed mats
(about 80% cover of water surface), the values averaged about 1.5 ppm.
These low values not only can be damaging to aquatic fauna, but
amidst swamp forest trees, prolonged cover by water hyacinth mats and
resulting restriction of gas exchange and direct exclusion of oxygen
must also further depress oxygen levels in the root zone. This is ad-
ditive to the stress of low oxygen brought about by standing water and
sediment deposited over the roots. Thinning of tree stands in areas
of chronic water hyacinth cover may be related to this. Seedlings>
which normally might have appreciable flooding tolerance, may do less
well in such low oxygen waters.
Flooding and Sedimentation Tolerances
The effects of flooding on the forest ecosystem are many and
varied. Control is exerted on the composition of tree stands through
inhibition of germination, mortalities to seedlings> and mortality °r
diminished competitiveness of larger trees.
4lj. J. Lynch, et_ al. , ^'Effects of Aquatic Weed Infestations
on the Fish and Wildlife of the Gulf States " (U. S. Department of
the Interior, Spec. Sci; Report, Volume 39, 1947).
42
Penfound and Earle, 1948, op. cit.
45
-------
Since no tree species of the area have seeds capable of germination
beneath water, the presence of floodwater at a site during the normal
germination time precludes the establishment of seedlings. For this
reason, successful sets of cypress seed in its normal habitat of long
hydroperiod are considered to be relatively infrequent events which
occur only during drier years. Water tupelo, black willow, red maple,
and cottonwood have seeds which germinate in late spring or summer,
when it is much more likely that the soil will be dry over a wide area.
Some cypress seed may also germinate at this time, although the opti-
mum period is early spring. Most of the other species have seeds which
germinate in early spring; consequently, there is little opportunity
for germination except on the highest lands, which are not flooded at
this time.
Seedling mortalities may occur if seedlings are completely cov-
ered by floodwaters for extended periods. Some species, especially
baldcypress and tupelo gum, have a relatively high tolerance, although
much depends on the oxygen content of water. Kennedy found that deep
flooding (10 - 15 cm above the tallest seedlings) until June 1, July 1,
and August 1, showed seedling survival rates of 93, 87. and 32%, re-
spectively, in water tupelo seedlings 46 cm in height.^ Seedlings
not totally covered by floodwater showed excellent survival rates.
Kennedy also simulated siltation by depositing sand about the flooded
seedlings. He noted that it decreased survival by about 9% at a mod-
erate depth of flooding (15 - 25 cm above groundline) and by about
33% for deeply flooded seedlings. It should be noted that silt and
clay deposition may cause further decline in survival.
In a study of submergence tolerance of several bottomland hard-
wood species, Hosner ranked the following species in order from most
to least tolerant: buttonbush, box elder, black willow, cottonwood,
green ash, American elm, sycamore, red maple, sweet gum, and hack-
berry.^
Perhaps the most important selective effect of flooding is that
due-to mortality or reduced competitive ability of trees larger than
seedling size. Broadfoot and Williston^ cite the classification of
. E. Kennedy, Jr., "Growth of Newly Planted Water Tupelo Seed-
lings after Flooding and Siltation," Forest Science (Volume 16, 1970).
J. E. Hosner, "Relative Tolerance to Complete Inundation of
Fourteen Bottomland Tree Species," Forest Science (Volume 6, 1960).
A5W. M. Broadfoot and H. L. Williston, "Flooding Effects on
Southern Forests," Journal of Forestry (September, 1973).
46
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Hall, Penfound, and Hess*^ which was developed from observations of
relative tolerance of trees flooded by reservoir construction. This
is an artificial system and does not necessarily indicate tolerances
to natural flooding cycles. According to their observations, some
common trees of the Atchafalaya Basin fall into two categories: (1)
moderately tolerant - box elder, river birch, water oak, American elm,
and sycamore; (2) tolerant - red maple, persimmon, green ash, honeylocust,
cup oak, cottonwood, water hickory, sandbar willow, water tupelo, and
baldcypress. Broadfoot and Williston^ noted that water tupelo was
highly resistant to flooding in clear water, but easily damaged by
muddy water.
Forest Types
Areas of long hydroperiod and low sedimentation rate are char-
acterized by the cypress-tupelo association. This association was
once very widespread over the basin, but increased sedimentation due
to the growing discharge of the Atchafalaya River and the construction
of the floodway have greatly diminished the area of the cypress-
tupelo habitat. These areas were also strongly affected by the cy-
press logging industry. Following the virtual clear-cutting of the
cypress stands, regeneration has been quite variable. Water tupelo,
in most cases, has regenerated more successfully than cypress so that
its representation in today's stands is greater than in those of the
past. The cutting of the trees no doubt altered many other aspects of
the community structure in substantial ways. The severe infestation
of the forest tent caterpillar (Malacosoma disstria) on water tupelo,
for instance, may be a result of the decline of some natural control
agent in the altered community.
The change in the spatial structure characteristics of the
cypress-water tupelo association must have substantially affected the
water balance of the habitats. The interception of rainfall and
transpiration from the virgin cypress forests were no doubt quite dif-
ferent than they are today. Hydroperiod and average depth of flooding
have increased following cutting. The construction of the floodway
and increased Atchafalaya discharge have also led to increases in
flooding. These trends may partly account for the relatively greater
success of water tupelo in the early stages of regenerative succession.
The tent caterpillar is also a factor in such water-balance considera-
tion and transpiration in the swamps.
^bT. F. Hall, et^ al., "Water Level Relationships of Plants in the
Tennessee Valley with Particular Reference to Malaria Control," Journal
of Tennessee Academy of_ Science (Volume 21, 1946).
*7Broadfoot and Williston, 1973, pp. cit.
47
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The sedimentation factor is critical in estimating the probable
future of the cypress-water tupelo areas because neither cypress nor
water tupelo seem to be able to survive rapid sedimentation. It is
likely, therefore, that this association will continue to diminish in
area within the floodway. It is possible to reduce the sedimentation
resulting from the normal flooding of Atchafalaya River by either
channelization or extended guide levees, but the substantial sediment
contribution during times of floodway use will remain. Each time the
floodways are used, a certain amount of area will become less suitable
for the cypress-water tupelo association. The early stages of such
change will be evident by increasing amounts of willow followed by
other species.
Of all tree species in the Atchafalaya Floodway, the willows are
best adapted to conditions of both flooding and sedimentation. This
is evident from their widespread occurrence as dominants or important
members in tree associations throughout the floodway. Their ability
to withstand flooding and sedimentation seems to be related to the
ready formation of both adventitious roots and aerenchyma tissue which
allow for aeration of the root system in times of low oxygen stress.
Willow is also a very prolific producer of wind-transported seed which
is capable of rapidly spreading to any suitable site. Stands of wil-
lows also appear to undergo a self-thinning process which prevents
stagnation in their generally rapid growth.
Cottonwood and sycamore are two other species that are adapted
to withstanding high rates of sedimentation. Few other woody species
have much tolerance, although there is a dependence here not only on
the quantity of sedimentation, but also on the quality. Sedimentation
by sandy sediment may be less damaging than that by fine sediment due
to the differing porosity and permeability. This quality difference
gives an important latitude to the sedimentation tolerance of the other
hardwood trees characteristic of higher ground.
Sediment exerts its impact primarily through its effect on the
root system. Since the increasing cover of the roots generally tends
to lower oxygen available to them, it is probable that varying tol-
erances to sedimentation are largely related to adaptations allowing
anaerobic respiration. Trees without such adaptation are quickly
killed. Black willow, cottonwood, and sycamore have an additional im-
portant adaptation in their ability to form new root systems quickly
which can replace the earlier ones. Green ash, pumpkin ash, and red
maple also have some ability to form secondary roots.
The lands of lowest hydroperiod show peak diversity of all non-
aquatic life forms. Trees include several species of oaks, few of
which have significant tolerance to flooding. Lianas are numerous
and important vegetational components. Understory and forest floor
communities reach their highest diversity and standing crops in these
forests. Wildlife food and cover conditions reach their optimal levels
48
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for the entire area with an abundance of mash, berries, and green
forage.
A vegetation map of the Buffalo Cove area shows a typical dis-
tribution of forest types related to the bowl-shaped topographic char-
acter of that area. Willow, cottonwood, and bottomland hardwood oc-
cupy the high rim formed by natural overbank and spoil deposition.
Away from the rim, willow and cottonwood become dominant due to more
frequent flooding coupled with a lesser, but still significant, rate
of sedimentation. The lowest, almost permanently flooded parts are
occupied by cypress-tupelo, with willow invading as a result of sedi-
ment influx through openings connecting the basin with the surround-
ing channels, where velocities and sediment load are high .(Figure 4-2).
Forestry Potential
The forestry value of the wetter bottomlands is a subject that
has attracted relatively little attention since these areas were cut
over for their virgin timber resources. This is partially due to the
difficult operating conditions in swamplands. A commonly held opinion
that such areas have inherently slow regenerative growth is not sub-
stantiated by fact. This view has probably arisen due to the many
areas in which stands are stagnant from excessive density or which
have been adversely affected by manmade drainage alterations Vir-
tually no skilled management practice has been applied to silviculture
in a wet bottomland situation in this area. Some managed cottonwood
plantings exist in higher terrain above U. S. Highway 190, but in the
remainder of the area there has been little or no value placed on tree
culture.
This attitude is still prevalent despite the fact that Hadley re-
ported early in this century that water tupelo compared favorably
with pines in pulpwood production potential. 48 Cypress has also been
shown to have a high growth rate on sites in which hydroperiod is not
overly prolonged. « In some cases at better-drained locations, one or
two successive harvests have been made of cypress since the first cut-
tings. Many other trees characteristic of sites somewhat less wet
than the cypress-tupelo zone are forms which should be of appreciable
interest to the forest industry. Among these, green ash is possibly
a highly desirable form for lands of lower hydroperiod, and cottonwood
for higher lands. Few of the other common trees of the lower-lvine
lands of the basin have been utilized significantly in the forest in-
dustry on a local scale although some are potentially useful. Willows,
48E. W. Hadley, "A Preliminary Study of the Growth and Yield of
Second-Growth Tupelo Gum in the Atchafalaya Basin of Southern Louisi-
ana," The Lumber Trade Journal (November 15, 1926) .
T « a of Bottomland Forest Species in Southeastern
Louisiana (M.S. Forestry Thesis, Louisiana StateUniv^r'sity, 19681 83 p.
49
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..,— ,. >• HAHttt «"C
CT«« \ /y/***"^'-/
1 \ y'y/V'nVv-/ '
^ \._iriivv# ;;;«'%/ •
•// Vegetation
/ Buffalo Cove flreo-Rtchofoloyo Bo/In. Lo.
LEGEND
C*"l "tsiss"0"000 [--'"£]"'"" *"•"*• "**
•« J W»10. COIIO<«00« ["» J "•"•« •'!'»•
[5i=]
IS
.~
IOITOM.MO H4MMOOO
* «w*ic» on onn i
H IUHWIC CANM
Figure 4-2. Distribution of forest types in the Buffalo Cove Manage-
ment Unit.
50
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for instance, have been extensively utilized by industry in eastern
Europe, particularly for pulp. If this practice were to appear in
this area, black willow could become an important forestry species
in the basin where it is so widespread because of its high sedimenta-
tion and flooding tolerance. A potential for utilization other than
pulp also exists. On some of the better-drained sites, black willow
can reach timber log size, and its wood is highly desirable for sev-
eral reasons.
Tupelo gum does not presently attain maximum growth rates due to
the heavy defoliation which typically occurs on them as a result of
caterpillars of the species Malacosoma disstria. In Alabama, U. S.
Forest Service workers found that over a period of five years, growth
was 50% greater (iix diameter at breast height) for uninfected plots.50
The various oaks are desirable not only for wood, but for their
mast production,which is essential for a variety of wildlife species.
Careful attention should be given in planning of the floodway in order
to provide adequate amounts of mast-producing hardwood forest. The
appropriate locales for this are areas of least frequent flooding and
lowest siltation rates. The water oak, overcup oak, and Nuttall oak
are the best-adapted forms for survival on such locations within the
floodway.
An important strategy for management of lower bottomland for-
ests is that of water-level manipulation. This can be used for var-
ious purposes, such as optimization of growth of a particular species
or elimination of competitor species. Water-level manipulation can
also be an aid to harvesting through flotation logging.
Water-level manipulation can be used not only as a forestry
strategy, but also for other purposes. Timely regulation of water
level may be incorporated as an aspect of water hyacinth-control pro-
grams to provide for a larger amount of dessication and oxidation of
organic materials. Obviously, control of water can be used in craw-
fish culture or in regulating habitat conditions for certain water-
fowl species. With careful attention, management practices can con-
sider all needs simultaneously.
The exact manner by which water-level regulation can be used
will be determined by the morphological and hydrological character
of a given site. Low dikes can be used to catch and hold water at
times of high water for storage over a period of lower stage. Dif-
ferent areas can be dewatered at various times depending on the re-
quirements of the particular species being managed. The overall de-
sign should aim at energy economy by using gravity as much as possible
for movement of water.
50R. C. Morris, personal communication (Stoneville, Mississippi
February, 1975).
51
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Not only must water be allocated according to the needs and re-
quirements of various species, but sediment must also be similarly al-
located. For instance, areas managed for willow pulpwood production
can be used as sediment traps from which clearer water can be trans-
ferred to areas managed for species not as tolerant to sedimentation
as willow. Gradual filling will lead to a need for rotation of use of
such areas.
Numerous innovative developments in forestry product utilization
are likely to further increase the value of forested areas, such as the
Atchafalaya Basin. Short rotation forestry, for instance, is a method
for production of young coppice-regenerated trees for fiber produc-
tion. Sycamore is a basin species which has been investigated for
short rotation culture, and it appears that its attributes of rapid
initial growth and good pulping qualities at four years of age are
favorable to this technique.51 Other species which regenerate well by
sprouts and which have relatively rapid early growth and good pulping
qualities are also suitable for this type of culture. Of the trees
typical of the basin, cottonwood, red maple, sweet gum, and possibly
the willows are suitable on various types of sites.
Utilization of the complete tree is an innovation which has been
receiving increased attention. In a review of this subject, Keays
sums it up by saying, "The tops should be used for pulp; branches for
pulp, chemicals or fuel; foliage as a source of chemicals ^every-
thing remaining for conversion to heat, power, and chemicals. This
touches on another area of promising innovation, that of the growing
SSSJScS industry which offers much hope of increasing efficiency
of forest yields of useful materials. The future of this already-
growing industry has been appraised recently by Goheen in a review
which fists numerous potential products that will contribute to ener-
gy, food, and chemical raw material supplies.»•»
5lKlaus Steinbeck, Short Rotation Forestry in the United States;
A Review (American Institute of Chemical Engineers,. Symposium Series,
Volume 70, 1974).
52j L. Keays, Complete-Tree Utilization of Mature Trees^ (Ameri-
can Institute of Chemical Engineers, Symposium Series, Volume 70, 1974)
75 p.
53D. W. Goheen, Silvichemicals - What Future? (American Insti-
tute of Chemical Engineers, Symposium Series, Volume 69, 1973).
52
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V
FISH AND WILDLIFE RESOURCES
The Atchafalaya Basin is well known by sport fishermen in the
State of Louisiana, and the basin ranks high among commercial fresh-
water fish production areas in the United States. Game fish species
in the basin include largemouth bass, bluegill, warmouth, and other
species. Several factors, acting both individually and in combina-
tion, create almost ideal conditions for fish populations in the
basin and maintain high annual fish production.
In addition to its immense fishery resources, the Atchafalaya
Basin is also home to numerous species of waterfowl and terrestrial
or semi-terrestrial species of wildlife. It is not surprising in a
water-dominated system such as the Atchafalaya Basin that many of the
animal species there are dependent, to a greater or lesser extent, on
the prevalent wet conditions for their well-being and livelihood.
Indeed, nearly all animal habitats in the basin, including the rela-
tively high natural levee ridges, can be classified as a wetland of
one type or another. Since water is as necessary as the presence
of nutrient minerals for organic production, it is perhaps this
overall wet character of the basin which accounts for, more than any
other factor, its high productivity.
Factors Enhancing Fish Production
Perhaps the most important feature affecting fish production in
the basin is the annual fluctuation in water levels and area covered
by water. Each spring, associated with high stages on the Atchafalaya
River, low-lying swamps and floodplain areas are filled with water.
At highest river stages, much of the area inside the floodway is es-
sentially one vast shallow lake. The area of aquatic habitat is
greatly increased. Newly flooded areas provide food for both fishes
and fish food organisms in the form of flooded terrestrial plants and
animals.
Nutrients brought in by river floodwaters and derived from
flooded areas increase the fertility of basin waters, spurring the
growth of phytoplankton and other aquatic plants. Phytoplankton can
be utilized directly by certain fishes (e.g., shad) or form the base
of a food chain leading to predacious fishes. Zooplankters which
feed on phytoplankton are important foods for larval and small adult
fishes.
54U.S. Department of the Interior, Fish and Wildlife Service,
Wetlands of the United States (Circular No. 39, Washington: U.S.*
Government Printing Office, 1956).
53
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Organic detritus, including dead leaves, stems, bark, and other
material of animal origin produced by in situ processes, as well as
imported detrital material brought in by river currents, also func-
tions as a food-web base. Detrital material is consumed directly
by crawfish, and the short detritus-crawfish-fish food chain is a
major reason for the high fish production of basin waters.
Spring floods coincide with the period of fish reproduction and
can induce spawning of certain species. Fish reproduction thus oc-
curs at a time when foods for young fishes are readily available. Buffa*
lo fish are influenced by floodwaters in their spawning activities
and often move into shallow, previously unflooded areas to spawn.
Spawning migrations of such fishes as shad, freshwater drum, and
gars are also influenced by rising water. Lantz attributed the
failure of largemouth bass to spawn in certain Louisiana impoundments
to the presence of a "repressive factor," or substance, secreted into
the water by the fish.56 Floodwaters in areas such as the Atchafalaya
Basin effectively dilute the repressive substance, resulting in good
spawns by largemouth bass and perhaps other sport fishes.
Besides the benefits of flooding of swamps and floodplain in the
spring, the drainage and partial or total dewatering of these areas
in the summer and fall periods provide additional benefits to fish
populations. Exposure of the swamp floor to the atmosphere allows
rapid aerobic decomposition of accumulated muck and debris and permits
the growth of terrestrial plants which will serve as a food source
for fishes or fish food organisms when"the area is again reflooded.
Dewatering of swamps concentrates fish populations into lakes and
bayous where smaller forage species,such as shad and young sunfishes,
maybe efficiently preyed upon by larger predators. Drainage of
swamps and backwater areas in the summer and fall is necessary for
good crawfish production in the following spring. Crawfish are im-
portant fish-food organisms in basin waters.
In general, the abundance of various fish-food organisms in the
basin is also a factor favorable to fish populations. Abundant
planktonic organisms, such as copepods and cladocerans, furnish food
for larval and juvenile game and commercial fishes as well as for
r Lambou, U.S. Environmental Protection Agency, personal
communication.
56Kenneth Lantz, "Natural and Controlled Water Level Fluctuations
in a Backwater Lake and Three Louisiana Impoundments'" (Louisiana Wild
Life and Fisheries Fish Division Bulletin No. 11, Louisiana Wild Life
and Fisheries Commission, Baton Rouge, Louisiana, 1974), 36 p.
57ibid.
54
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the adults of small forage fishes. Various insect larvae, worms,
snails, clams, amphipods, isopods, and freshwater shrimp furnish*
food for forage fishes, which in turn are fed upon by more predacious
game species. Tremendous numbers of crawfish in the spring provide
a vast food source for many fish species. Lambou and Lantz have
pointed out the importance of crawfish as a fish-food organism in
the basin.->°»->y Bryan et al. found crawfish in 9 out of 14 fish
species which were examined for stomach content.60 Crawfishes also
serve as food for a variety of other animals, including aquatic and
terrestrial forms.
Predacious freshwater fishes in the basin may benefit from the
migration of certain marine fishes and blue crabs into the area.
Striped mullet, particularly, are abundant and widespread in basin
waters. Crabs and mullet are undoubtedly eaten by gars, largemouth
bass, and other predators.
The major requirement, then, for maintaining the present value of
the fishery resource is maintenance of, insofar as possible, those con-
ditions which support the resource. Drainage of backwater swamps and
lakes is clearly at odds with fish production; aquatic habitats must
necessarily be preserved. Fish populations in the Atchafalaya Basin
are adapted to annual water-level fluctuations' and are dependent on
them for high productivity. Thus, the present fluctuating water-level
characteristics must be maintained or the value of the resource will
be decreased.
Factors Enhancing Crawfish Production
The two commercial crawfishes of the Atchafalaya Basin are con-
sidered together in this report. Differences in mating and spawning
seasons, foods, and microhabitats undoubtedly occur between the two
species, but have been little studied. The crawfish has been the most
valuable commercial species harvested in basin waters in the past seven
years. It also serves important ecological functions. Crawfish feed
on small worms and insect larvae living in the bottom mud and on
living aquatic and submerged terrestrial plants and plant detritus.
->8V. W. Lnmbou, "Utilization of Macrocrustacean's for .Food by
Freshwater Fishes in Louisiana-and-Its Effect on the Determination
of Predator-Prey Relations" (Volume 1, ,No. 1 Progressive Fish Culturist,
1961).
1974, op. cit.
60Bryan £t al., 1974, op. cit.
55
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In general, the water requirements for crawfish are well known.
Crawfishermen are often able to predict the relative abundance of
crawfish before a given season by noting water levels in the swamp.
If water in the swamp begins rising in the late fall (by November),
and if a high water level is maintained through the winter period, then
there is generally a good harvest of crawfish during the following
spring. Low water levels during the late fall and winter generally
forbode a poor crawfish season. If water levels remain high, however,
beyond the usual crawfish season (the bulk of the harvest is in by the
end of June) and into the summer months, then the next year's harvest
is low. A pronounced drop in water levels during the summer and early
fall, so that much of the swamp floor is exposed, is necessary for a
good harvest during the following season. Crawfish are adapted to
alternating wet and dry conditions, and it is probably the annual
cycle of flooding and draining over a large area that is responsible
for the high production of crawfish in the Atchafalaya Basin.
Water levels are closely linked to the life cycle of crawfish.
In general, the rising and high water periods in the late winter and
spring are the periods during which growth and maturity of young craw-
fish occur. The latter part of this period is when most crawfish
harvest takes place. Mating of crawfish occurs "whenever mature males
(form I) and females come together in shallow warm water."61 Although
it is likely that some mating activity occurs on an almost year-round
basis in the basin (excluding the coldest months), most mating probably
begins in May and June and continues through the summer during the
falling and low water periods. In the summer, in response to low water
levels, crawfish burrow into the bottom mud. Burrowing may also be to
some degree a post-mating response, since some crawfish in farm ponds
begin to burrow after the peak of the mating period before water levels
have dropped appreciably.62 However, when water levels in the swamp re-
main high through the summer, many crawfish do not burrow and thus re-
main exposed to aquatic predators.
Egg-laying begins about two months after mating and occurs mostly
during the summer low-water period from about June through September.
The eggs are held by a sticky substance (glair) on the abdominal ap-
pendages of the female. Eggs hatch after two to three weeks, depending
on temperature, and the hatching period extends from about July through
October. Both egg-laying and hatching can occur while the females are
still in burrows, but at some time during this period the females will
leave the burrows, often after a rainfall, and move to rainpools or
"^George H. Penn, Jr., "A Study of the Life History of the Louisiana
Red-Crawfish, Cambarus Clarkii Girard"(Ecology. Volume 24, No. 1, 1970).
62Cecil LaCaze, "Crawfish Farming " (Louisiana Wild Life and
Fisheries Bulletin No. 7, Louisiana Wild Life and Fisheries Commission,
Baton Rouge, Louisiana, 1970), 27 p.
56
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other flooded areas. The young crawfish cling by their claws to the
swimmerets of the female where they undergo at least two molts.
After the second molt (5 days after hatching), they are ready for an
independent existence, but they may remain attached to the female for
a longer time.
The critical period in the crawfish life cycle occurs when young
crawfish leave the female to go foraging on their own. Lack of water
in the basin at this time is a severely limiting factor on crawfish
production. Heavy autumn rains are beneficial to the young crawfish
because they provide aquatic habitats which are free from predator
fishes. However, if rain does not come, many young crawfish probably
die from lack of aquatic habitat.
Best crawfish years are usually those when the river has begun
its annual rise during the late fall or early winter of the previous
year and remains high throughout the spring season. Similarly, poor
crawfish years usually occur when the river does not begin to stead-
ily rise until February or March of the same year, or when river stages
were high through the summer of the previous year. Due to poor data,
no precise relationship can be established between early river rises
and increased crawfish harvests. A direct relationship seems probable,
however, because of the necessity of aquatic habitats for young craw-
fish during the fall of the year. The best crawfish production year
on record (1973) was caused not only by the abundance of water during
the spring of that year due to the opening of the Morganza Floodway,
but also by the high stages of the Atchafalaya River,which caused
flooding of backwater areas as early as October of 1972.
Backwater flooding of swamps in the fall of the year also intro-
duces predator fishes which consume a great number of young crawfish.
Losses due to predation by fishes and other predators are probably
not as great, however, as losses incurred by a lack of water in the
fall of the year. Many crawfish may be able to find escape cover
amongst flooded vegetation. It is possible that the deliberate in-
troduction of river water to allow for flooding of backwater areas
by around the first of November (in years when this does not occur
naturally) would be beneficial to crawfish production.
Requirements for maintaining high crawfish production in the
basin are 1) maintenance of the large area of aquatic habitat,
2) continuation of annual water-level fluctuations, and 3) elimina-
tion of high water levels during the summer and early fall. Addi-
tionally, earlier fall flooding in some years may be beneficial to
crawfish production.
While overbank flow of the Atchafalaya River is a major con-
tributor to the high productivity of the Atchafalaya Basin, it is
57
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also a major contributor to the eventual elimination of many of the
aquatic habitats in the basin. Each overflow of the river intro-
duces sediment into swamps, lakes, and over the flood plain. Sedi-
mentation in the Buffalo Cove area is estimated to have occurred at
a rate of about 0.03m (O.lft)/year over the past 40 years (Figure 3-2).
As this process of sedimentation occurs year after year, the end re-
sult is the elevation of the floodway floor. The Corps of Engineers
has estimated that the average thickness of the sediment fill between
the east and west protection levees and south of the end of the
Atchafalaya River guide levees over the 18-year period prior to 1950
is about ,99m (3.3ft).63 A comparison of the diagrams of the Grand
Lake area through the period 1917 to 1972 shows in a striking manner
the filling in with sediment of this once vast lake area.64 It should
be pointed out that the lowest places, such as lakes, are the first to
fill. Although increasing amounts of sediment are now being trans-
ported through the middle basin and being deposited in the emerging
delta of the river in Atchafalaya Bay, it can be expected that sedi-
mentation in the middle basin in such areas as Grand Lake, Six Mile
Lake, Flat Lake, and in other areas will continue to occur.
Sediment materials, then, fill in aquatic habitats in the basin,
making them progressively shallower. Certain tree species (bald-
cypress, tupelo-gum) are not tolerant of sedimentation deposited over
their roots and gradually become replaced by more sediment-tolerant
species as cottonwood, willow, and sycamore. Changes such as this
among the dominant species of a community probably have far-reaching
effects on other members of the community.
Seemingly, then, those processes which the Corps of Engineers
desires to stop (overbank flow in the Atchafalaya River and resultant
sedimentation) are not completely incompatible with long-term main-
tenance of the natural features of the basin which can hopefully be
preserved. Overbank flow is needed to maintain the productivity of
aquatic resources, but the sediment is not needed, and indeed, is
detrimental to the long-term viability of the system. The overall
requirements, then, for maintaining the value of the fishery resources
are:
U.S. Army Corps of Engineers, Flood Control. Mississippi
River and Tributaries, Atchafalaya Basin Floodway. Louisiana (General
Design Memorandum, Prepared in the Office of the District Engineer,
U.S. Army Engineer District, New Orleans, Louisiana, 1963).
64Coastal Environments, Inc., 1974a, op_. cit.
58
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1) a continuation of the annual watering and de-
watering sequence, and
2) a minimization of the amount of sediment leaving
the Main Channel and larger distributaries.
Since sediment is carried by river water, it will be necessary to con-
trol the amount of river water entering backwater swamps and lakes in
order to limit the amount of sediment entering these areas.
Waterfowl
The Atchafalaya Basin is located near the southern terminus of
the Mississippi Flyway, which is utilized by some 8.5 million water-
fowl, or approximately 30% of the continental waterfowl population.65
Major species of ducks occurring in the basin include the following:
Puddle Ducks Diving Ducks Mergansers
Mallard Ring-necked duck Hooded merganser
Gadwall Canvasback Common merganser
Pintail Lesser scaup Red-breasted merganser
Blue-winged teal
Green-winged teal
American wigeon
Shoveler
Wood duck
There are three general habitat types for waterfowl within the
Atchafalaya Basin: the coastal marshes, open-water lakes and streams,
and forested wetlands.6" All of the ducks listed above utilize the
coastal marshes. However, of the three types of ducks, the puddle
ducks, particularly wood ducks and mallards, are frequently found in
the freshwater lakes, streams, and swamps. The wood duck is a year-
round resident nesting in the swamps of the Atchafalaya Basin. Diving
ducks are usually most numerous in more saline habitats, such as
brackish water lagoons and bays. A relatively few diving ducks do,
however, occur in the freshwater habitats of the middle and northern
basin each year. The lower Grand Lake and Six Mile-Lake area, in the
vicinity of Tiger Island, is intensively utilized as a wintering area
65U.S. Department of the Interior, 1974, op. cit.
66Hugh A. Bateman, Needs and Goals of the Atchafalaya Basin
Swamp (Atchafalaya Basin Management Study, Baton Rouge, Louisiana,
1973), 27 p.
59
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by 300-500 canvasbacks during the winter. Canvasbacks the most
famous and the most highly esteemed of our ducks, O'.have in recent
years been declining in numbers as a result of the cumulative loss
of both nesting and wintering habitat.
Of the mergansers, only the hooded merganser is regularly
found in the woode.d portions of the Atchafalaya Basin. A few
hooded mergansers may nest in the basin in the summer.
Besides ducks, the Atchafalaya Basin is utilized by thousands
of coots each winter. A significant number of blue/snow gef^e winter
in the coastal marshes of western Terrebonne Parish in the vicinity
of Lost Lake and Pointe au Fer Island.
Bateman states that the value of the Atchafalaya Basin to
waterfowl "can be measured in two important respects: 1) as a
large high-quality wintering ground for migratory waterfowl, and
2) as'one of the largest units of quality wood duck production
habitat remaining in the United States.
The general requirement for maintaining waterfowl values is
obviousf .he Atchaf laya Basin -^.2^^^SSS^^
flooded area or it w*11.}~e "J/^J*lff water to backwater swamjs
flood control project which would cut ott tlcuiarly> the
and lakes would destroy "f^'f^^f luxations must be main-
present natural pattern of water le be reduced. The
cu^nt^ncfof ll^lT^llln the late summer and fall
followed by high water levels in the winter and spring allows for
the growth of important waterfowl food plants during the low-water
perioHnd for their utilization by waterfowl during the high-water
period. The control of water levels for the increased production
of waterfowl food plants is an established practice in waterfowl
habitat management.
Other problems and needs related to waterfowl in the Atchafalaya
Basin discussed by Bateman concern time of fall flooding, water
hyacinth coverage, siltajion, and provision of waterfowl refuges to
attract and hold birds.
67Francis H. Kortright, The Ducks. Geese and'Swans of North
America (Wildlife Management Institute, Washington, D.C., 19
-------
During some years and in some areas of the basin, due to either in-
adequate autumn rainfall or to delayed stage increases in the
Atchafalaya River, or both, a lack of water in October and November
causes migratory waterfowl to avoid this area in favor of wetter
locations. Bateman suggests that a controlled manipulation of swamp
and backwater lake water levels "that would allow a gradual rise 2
to 4 inches a week, beginning about two weeks prior to the open '
hunting season, would greatly benefit waterfowl use and hunting."71
It should be pointed out, however, that it would be difficult to
introduce river water into backwater swamps and lakes during the
periods when the river is falling or at low stage. The only way this
could be practically accomplished at present is by increasing the
river stage to allow more Mississippi River water to enter the flood-
way through the Old River control structure. This is not, however a
new idea. The Louisiana Wild Life and Fisheries Commission has recom^
mended for many years that the Old River control structure be operated
as a variable control structure for fish and wildlife management
purposes. Bateman 's suggestion for earlier fall flooding during
Waterfowl use is consistent with recommendations
report for eariier fan fi°°ding t
to w^erfowl. On the
P°or waterfowl food plants which may grow so
^~lnate mUCh °Pen-water habitat and make access to
di"lcult- Water h?aclnth control in the basin is not
°f Sprayin8 effo«s (with the herbicide 2, 4, D) are
Waterwa*s -vigable. The pest plant 'has thus
areas away from channels where spray boats
acswampareaS f^ method °f herbicide -PPUeatlo
hyacinths rather "" ava"able' Cold vinters kill back water
rhr
-hyacinths
The Louisiana Wild Life and Fisheries Commission has recently
t^ctio f biolof^l control of water hyacinths with the'in-
troduction of an apparently host-specific South American weevil
exPerlmental «eas. The larva and adult
oTTn . arva an au
of the weevil feed on the leaves of the water hyacinth plant. It is
not thought that control will be accomplished by the direct feeding
activities of the weevil, but that the scars and injuries to the plant
71lbid.
72Ibid.
61
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tissue caused by the feeding activities will render the water hyacinth
plant more susceptible to plant diseases caused by rusts or other
organisms. At the present time, there is little data available on
the introduction or effects of the weevil, but there has been some
spread of the weevils to areas outside of the immediate introduction
sites.75
Sediment deposition in the Atchafalaya Floodway is a major
problem that is discussed at length in other sections of this report.
Siltation in the floodway has over the years eliminated much open
water habitat for waterfowl and has made hunter access to waterfowl
areas difficult. Certain areas in the floodway (Duck Lake) have suf-
ficiently clear waters to allow the growth of submerged aquatic plants,
such as water celery (Vallisneria sp.), which are important waterfowl
food plants. Encroachment of highly sediment-charged waters into
these areas will create conditions unfavorable to the growth of these
plants.
Bateman cites a need for waterfowl refuges in the Atchafalaya
Floodway.74 Most of the land in the floodway is privately owned, and
a large area is leased for hunting purposes to private hunting clubs.
The State of Louisiana does own some land within the floodway which
may be suitable for the establishment of a waterfowl refuge. However,
for greatest waterfowl benefit, refuges should be established in dif-
ferent habitat types (e.g., cypress-tupelo swamp areas, open water
bodies, main river channel areas). Bateman recommends the establish-
ment of "at least A small (1,000 acre) refuges (or rest areas)...
somewhere in the basin."75 Refuges for waterfowl (where hunting is
not allowed in the open season) greatly benefit hunting in areas out-
side of the refuges because more birds are attracted to the area, and
their residence time is increased.
Furbearers
Furbearers in the Atchafalaya Basin include nutria, raccoons,
mink, otters, opossums, muskrats, striped skunks, beavers, bobcats,
coyotes, and foxes. The alligator is classified as a furbearer in
Louisiana, but it is not currently exploited in the basin. Nutria,
Lee, personal communication.
74Bateman, 1973, op. cit.
.62
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mink, and raccoons comprise a large portion of the total reported
catch and value in the upper and middle basins,^° while nutria,
muskrats, and raccoons are probably the most important furbearers in
the marsh area of the lower basin. A few otters are caught in both
areas each season. Opossums are taken in significant numbers in
spite of the low value of their pelts. The American beaver has only
recently extended its range Into the Atchafalaya Basin. Its pelt
currently has a low market value, and few beavers are trapped.
Skunks, bobcats, foxes, and coyotes are taken in insignificant numbers
or not at all.
The greatest value of the basin as a fur-producing area is In
the production of mink and raccoon pelts. Approximately 34% and 25%,
respectively, of the mink and raccoon pelts harvested In Louisiana
during the 1971-72 trapping season came out of the natural Atchafalaya
Basin. Although more nutria are caught In the area (as well 'as state-
wide) than any other furbearer, nutria production is low when compared
to state-wide figures.''
Besides their pelt value, the carcasses of nutria, raccoons, and
opossums are sold either for pet or caged mink food or human consump-
tion. Food, habitats, and other pertinent information concerning the
major furbearers in the basin are discussed below.
Nutria (Myocastor coypus)
The nutria has in the 37 years since its introduction come to be
the most valuable furbearer in the state on the basis of numbers of
pelts taken per year and overall value of pelts. Nutria live in marsh
and swamp areas and may also be numerous near drainage ditches, ponds,
and lakes In more upland areas. They are herbivores which feed on a
large variety of plants including maidencane, wiregrass, three-cor-
nered sedge, bulltongue, alligatorweed, pondweeds, pickerelweed, duck-
weed, and other plants. Water hyacinths are also eaten by nutria, but
not enough to control the pest plant as once was hoped. They may
sometimes invade sugarcane or rice fields where they do great damage.
76j. D. Nichols, A Survey of Furbearer Resources In the Atchafalaya
River Basin, Louisiana (Unpublished Master's Thesis', Louisiana State
University, Baton Rouge, Louisiana, 1973), 184 p.
63
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Nutria occur in both marsh and swamp habitats in the Atchafalaya
Basin. Both freshwater and brackish marshes are utilized by the
nutria, but the center of their abundance is probably in the fresh-
water marshes where there exists the greatest variety of preferred
food plants. All of the forested wetlands in the Atchafalaya Flood-
way furnish habitats for nutria. In the upper and middle basin,
cypress-tupelo swamps, according to Nichols, are preferred trapping ?8
areas not only for nutria, but for other types of furbearers as well.
Raccoon (Procyon lotor)
As has been mentioned, approximately one-fourth of the raccoon
pelts harvested in the State of Louisiana during the 1971-72 trapping
season were taken from the natural Atchafalaya Basin,79 and a similar
percentage is probably taken on an annual basis. They occur through-
out the Atchafalaya Basin in marsh, swamp, and bottomland hardwood
areas. Raccoons in the coastal marshes (Procyon lotor meftalodous)
have a more yellowish colorSO and a lower pelt-value81 than the swamp
and woods-dwelling raccoons (Procyon lotor varius) which occur through
out the rest of the state.
Foods eaten by raccoons include crawfish, crabs, snails, clams,
insects, acorns, blackberries, grapes, and other items of both animal
and vegetable nature.82,83 They are known to prey on alligator eggs
and young in the coastal marshes.84
78Ibid.
80George H. Lowery, Jr., The Mammals of Louisiana and Its
Adjacent Waters (Published for the Louisiana Wild Life and Fisheries
Commission by the Louisiana State University Press, Baton Rouge,
Volume 24, 1974a), 565 p.
8lA. W. Palmisano, Commercial Wildlife Work Unit Report to Fish
and Wildlife Study of the Louisiana Coast at the Atchafalava Basin.
Volume 1 (1971).
82LOWery, 1974a, op. cit.
83Nichols, 1973, O£. cit.
Joanen, Nesting Ecology of Alligators in Louisiana (Pro
ceedings of the 23rd Annual Conference of the Southeastern Associa-
tion of Game and Fisheries Commission, 1969) .
64
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Mink (Mustela vison)
Although the coastal marshes produce an abundance of mink pelts
annually, the more inland swamps and bottomland hardwood areas in the
state probably contain higher populations of this animal. St. James
Parish, on the Mississippi River, produces from 10 to 14 thousand
mink annually.8i During the 1971-72 trapping season, approximately
3/*% °f8^he mlnk harvested in the state came out of the Atchafalaya
Basin. "The abundance of the species in the bottomland swamps has
been attributed to the presence of crayfish, one of its main items
of food in these areas."87
Minks are carnivorous, feeding on aquatic animals such as
crawfish, crabs, fish, and frogs, and terrestrial species such as
rats, mice, and rabbits. In the marsh, mink are major predators on
muskrats.
Otter (Lutra canadensis)
Otters are the most valuable furbearers in Louisiana based on
the value of single pelts. The average price paid for these pelts since
1940 has been $14.74, with a high price of $42.00 being paid during the
1972-73 season.88 Otter pelts are thick, lustrous, and very durable.
Otters are inhabitants of wetland areas, including marshes
and swamps. Palmisano states that the average catch of otters in
the marsh is less than one otter per 2,000 acres and that the most
productive marshes are fresh to brackish types.89 Swamp areas in the
state are not as intensively trapped as the coastal marshes, and
statistics on the harvest of the various types of furbearers from
different habitat types or geographic areas are almost non-existent
except for a few state-owned lands. No direct comparison can be
85
OJLowery, 1974a, op. cit.
86Nichols, 1973, op_. cit.
87
Lowery, 1974a, op. cit.
88Ibid.
89Palmisano, 1971, op_. cit.
65
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made, therefore, on the abundance of otters in swamp and marsh
habitats on the basis of trapping records. Swamps, however, are
perhaps somewhat better habitats for otters than the coastal
marshes because of the greater abundance of den sites around tree
bases and the somewhat greater food availability in the form of
crawfish.90
Otters are carnivores, feeding on fish, frogs, turtles, snakes,
crawfish, and crabs. Terrestrial animals, such as small rodents,
are occasionally taken.91 Because of their fish-eating habits, ot-
ters sometimes swim into hoop nets set by commercial fishermen,
where they drown.
Opossum (Didelphis virginiana)
Opossums occur throughout Louisiana in wooded areas, marshes,
cleared fields, and in the vicinity of human habitations. They are
abundant in the Atchafalaya Basin. Opossum pelts have a low value,
and probably many more opossums are taken by trappers than those
whose pelts are actually prepared for the market. Their flesh is
valued at about $0.20 per pound.
Opossums consume insqcts, earthworms crawfish, carrion, acorns,
wild grapes, blackberries and other fruits.yz Around houses, they
frequently turn over garbage cans in search of food. The omnivorous
habits of opossums are one reason for their great success and abun-
dance.
Muskrat (Ondatra zibethicus)
The muskrat has long been and continues to be one of the main-
stays of the Louisiana fur industry. Although its importance has
been somewhat overshadowed by that of the nutria in recent years,
good catches of muskrats are still made in the coastal marshes on a
year-to-year basis.
90Nichols, 1973, op_. cit.
91Lowery, 1974a, op. cit.
92Nichols, 1973, op. cit.
66
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In the Atchafalaya Basin, muskrats occupy both swamp and marsh
habitats. They are much more abundant in marsh habitats, however,
for a variety of reasons. O'Neil and Palmisano have established that
muskrats' preferred habitat in Louisiana is in the brackish-water
marshes occurring in the coastal zone.93'9^ The climax vegetation in
this type of marsh is dominated by wiregrass (Spartina patens).
Muskrat abundance in brackish-water marshes is, however, closely
linked to the abundance of the sub-climax plant, three-cornered
sedge (Scirpus plneyi). Whenever a wiregrass marsh is disturbed by
fire or by temporary saline-water inundation, three-cornered sedge
comes in temporarily until the climax plant, wiregrass, recovers
and chokes it out. During this period, muskrats increase greatly
in abundance and, for proper marsh management, must be removed by
trapping,or severe "eat-outs" (where muskrats completely consume
the existing vegetation including root systems, resulting in the
break-up of marsh soils) will occur. Muskrat eat-outs, depending
on their severity, take from one to several years to be revegetated,
during which time the value of the area is greatly reduced for
muskrats as well as other inhabitants of the marsh.
In the Lower Atchafalaya Basin, however, marshes are pre-
dominantly freshwater in character because of the heavy dilution
effect of Atchafalaya River discharge. Although muskrats occur in
freshwater.marshes, they never reach high population levels as in
brackish water marshes.
Muskrats are found in swamp habitats in low numbers as com-
pared to brackish marshes. In these areas, muskrats do not build
houses as they do in the marsh, but construct bank dens or occupy
burrows dug by other animals. Swamp habitats, especially those in
the Atchafalaya Floodway, are generally subject to rather high
changes in water levels. Spring flooding of swamps in the Atchafalaya
Basin probably causes some loss of nest young due to drowning. In
addition, high quality muskrat food plants are not abundant in swamp
habitats.
Food habits of muskrats vary according to the type of habitat
they occupy. In freshwater marshes, they eat maidencane, cattails,
roseau cane, Sagittaris spp., sedges, and some animal matter. In
93Ted O'Neil, The Muskrat in the Louisiana Coastal Marshes
(Federal Aid Section, Fish and Game Division, Louisiana Department
of Wild Life and Fisheries, New Orleans, Louisiana, 1949), 152 p.
9^Palmisano, 1971, op. cit.
67
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swamps, muskrats eat Sagittaria spp., pickerelweed, lizard's tail,
alligatorweed, and other plants. In freshwater areas, they feed
somewhat more heavily on animal materials than they do in brackish
water areas. Animals eaten include fishes, crawfishes, crabs, and
mussels.95,96
Furbearer Requirements
The main requirement for the continued abundance and well-being
of furbearers is the preservation of the various wetland environments
as they presently exist. Most of the furbearers in the basin are
traditionally associated with, and are actually most numerous in, wet-
land environments. If a single reason for the fitness of the basin
environments to support fur-bearing mammals can be pointed out, it is
the overall wet character of the forest and grassland habitats in the
basin,which is most important and which should be preserved.
Game Species of_ Wildlife
Major game species in the basin are deer, squirrels, rabbits,
woodcock, and doves. These species are frequently hunted. Other
game animals present include turkeys, bears, quail, foxes, raccoons,
opossums, bobcats, snipe, and rails. These last-named species are
infrequently hunted due to low population numbers or to a lack of
hunter interest.
White-tailed Deer (Odocoileus virginianus)
White-tailed deer occur throughout the Atchafalaya Basin, in-
cluding swamp and marsh areas. Highest populations, however, are
found in better-drained areas in the upper basin, where the popula-
tion densitv is estimated at one deer per 20-30 forest acres. ^g
This density must approach the carrying capacity of the range.
95o'Neil, 1949, op_. cit.
96Lowery, 1974, op. cit.
97Needs and Goals Sub-Committee, Atchafalaya Basin Management
Study, Needs and Goals of the Atchafalava Basin Swamp (Atchafalaya
Basin Management Study, Baton Rouge, Louisiana, 1973), 27 p.
98Dr. Lyle S. St. Amant, Louisiana Wildlife Inventory and
Management Plan (Louisiana Wild Life and Fisheries Commission, New
Orleans, Louisiana, 1959), 329 p.
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The upper basin area is forested with bottomland hardwood species
such as water oak, Nuttall oak, sweet gum, red maple, bitter pecan,
willow, cypress, and tupelo gum. Many of the larger cypress and tupelo
gum trees in the upper basin are remnants of swamps which occurred in
this area prior to construction of guide levees on the Upper Atchafalaya
River. Guide levee construction deprived these swamps of much of their
water source, resulting in partial drainage of the swamp area and al-
lowing the growth of competitive species more suited to drier sites.
Vegetative and water-level changes have increased the value of the
area as a habitat for deer.
Food.conditions for deer in the present bottomland hardwood areas
are excellent. Items reported as deer foods in alluvial bottomlands
and which are abundant in the upper basin are buds, leaves and
twigs of young trees such as cypress, sweet gum, various oaks, red
maple, ash, and bitter pecan, shrubs such as buttonbush, and vines
such as greenbriar and rattan vine." Acorns and other mast, eaten
by deer in the fall, are abundant in the upper basin.
In the middle basin (in general, that area of the natural
Atchafalaya Basin between Interstate Highway 10 and Morgan City),
elevations are lower and backwater areas are subject to seasonal and
prolonged flooding, the population density of deer is estimated at
one deer per 50-60 acres.100 Deer in this area make much use of
low, natural levee ridges and spoil banks which constitute the high-
est available land. Vegetation and foods occurring on these ridges
are similar in kind to those described for the upper basin, but
smaller in extent. The area of unflooded land available to deer
changes as water levels in the swamp rise and fall. While deer will
enter the shallow margins of swamps to seek food, the deeper swamps
are not ordinarily used except for escape cover or during times of
food stress.
Little is known of deer or deer conditions in the marsh area
of the lower basin. Marsh deer are not often hunted because of the
difficulties faced by the hunter in movement through and transport
of killed animals from the marsh. Deer in the marsh again utilize
available high land, including spoil banks and the very low natural
levees of bayous. Most of the more desirable deer food plants in
the marsh are confined to the high land areas.
"ibid.
°°Needs and Goals Sub-Committee, 1973, op. cit,
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Squirrels (Sciurus niger and Sciurus carolinensis)
St. Amant considers the Upper and Lower Mississippi River alluvial
plain, including the Atchafalaya Basin and other large river flood plains
in the state, to be the best squirrel range in Louisiana and pos-
sibly in the United States.101 Two subspecies of gray squirrels
(Sciurus carolinensis) and three subspecies of fox squirrels (Sciurus
niger) occur in Louisiana. Those inhabiting the Atchafalaya Basin
Irf-Sciurus carolinensis fuliginosus and Sciurus niger. subauratus.
Gray squirrels are known to prefer dense, bottomland habitats, while
fox squirrels prefer more open hardwood or mixed pine-hardwood
forests.10? Sciurus niger subauratus is, however, an exception in
this regard and is found in bottomland hardwood areas and in cypress-
tupelo swamps.103 Although gray squirrels are somewhat more numerous
statewide than fox squirrels, St. Amant found on the basis of four
years of bag checks, that fox squirrels slightly outnumbered gray
squirrels in the Mississippi alluvial plain 10* It is not known
whether this condition obtains in the Atchafalaya Basin, with its
more extensive swamps.
The best squirrel habitat in the basin, again, is in the upper
basin above Interstate Highway 10.105 This area contains a greater
percentage of mast-bearing trees such as wateroak, overcup oak,
pecan, and hickory, than the middle and lower parts. On a north-
south gradient associated with drainage and sedimentation, the basin
Is vegetated by bottomland hardwoods in the northern end, becoming
increasingly dominated by willow to the south, with the most un-
altered cypress-tupelo swamp areas occurring at the lowest end. This
overall picture is complicated somewhat by the bottomland hardwoods
occurring on ridges in the lower and middle basin. Squirrel numbers
and distributions can perhaps be related to vegetative types, with
highest populations occurring in bottomland hardwood areas and lowest
numbers occurring in a large area of the middle basin which is
dominated by black willow. Although squirrels often eat the tender
101St. Amant, 1959, op_. cit_.
102Ibid.
103 Lowery, 1974a, op. cit.
104St. Amant, 1959, op_. cit..
105Needs and Goals Sub-Committee, 1973, op., cit.
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buds and leaves of willows in the spring, the availability of other
high quality squirrel foods is probably not as high in willow-dom-
inated areas, especially on a year-round basis, as in the other
vegetative types.
Rabbits (Sylvilafius floridanus and Sylvilagus aquaticus)
Two species of rabbits are found in the Atchafalaya Basin. Ac-
cording to Lowery, the cottontail rabbit (Sylvilagus floridanus) is
most frequently found in more open habitats such as pastures, grassy
fields near croplands, and the like, while the swamp rabbit (Sylvilagus
aquaticus) prefers wooded areas, swamps, and marshes.106 St. Amant,
however, treated both species as farm game.107 Undoubtedly, there is
some overlap in habitats occupied by the two species, but, in general,
swamp rabbits inhabit forest areas, and cottontails are found most
often in or near cleared areas.
Rabbit populations are generally high in areas where habitat con-
ditions are suitable, in spite of heavy hunting pressure and high
mortality due to predation by hawks, owls, bobcats, and other predators,
High numbers are maintained by the high breeding rate of rabbits and
their general adaptability to a wide variety of habitat conditions and
food plants. Besides their usefulness as game animals, rabbits play
an important ecological role as a source of food for predacious birds
and mammals in the basin.
Woodcock (Philohela minor)
The American woodcock, which is mostly a winter resident in
Louisiana, is not a major game bird in the state,108 and most wood-
cocks are killed incidentally by hunters seeking other game. The
Atchafalaya Basin is, however, a major wintering area for woodcock
in the United States, and woodcock hunting is more prevalent in the
basin than in other areas of the state. These birds seek heavily
wooded areas with dense undergrowth for cover during the daylight
hours and fly into wet agricultural fields or other cleared areas at
night to probe for earthworms or other ground-dwelling organisms.
106Lowery, 1974, op_. cit.
107St. Amant, 1959, o£. cit.
108
Ibid.
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Mourning Dove (Zenaida macroura)
The mourning dove is a year-round resident in Louisiana. How-
ever, its numbers are greatly increased in the winter months with the
arrival of migrants from the north. Mourning doves are popular game
birds in the state. They are most abundant in and near cleared lands
and agricultural areas, where they feed on the seeds of weeds, grasses,
and cultivated plants, such as doveweed (Croton sp.), ragweed, corn,
soybeans, rice, and sorghum.
Most of the doves in the basin occur in the cleared agricultural
areas in the northern basin and in cleared areas on each side of the
floodway. These are also the areas where they are most frequently
hunted. St. Amant states that the Lower Mississippi-Atchafalaya al-
luvial plain "... no longer supports the large [dove] concentrations
that it supported in earlier years"*09 and suggests that clean farming
practices,such as winter plowing, increased grazing, and a decrease in
rotation of legumes, grains, and fallow fields.have eliminated much of
the natural and planted dove foods in the area. Since 1959, however,
a tremendous increase in soybean acreage may have partially improved
this condition.
Black Bears (Euarctos americanus)
A few native Louisiana black bears were known to occur in the
Lower Atchafalaya Basin in the early 1960's.11U In the mid-1960 s,
the Louisiana Wild Life and Fisheries Commission introduced 130 bears
into the northern part of the basin in Pointe Coupee Parish. Although
many of these bears wandered widely, an unknown number remained in
the area and have reproduced. The hunting season on bears (a big
game species) has been closed since the early 1960»s except for this
past 1974-75 hunting season,when bear hunting was allowed in an area
near the site of introduction. At least one bear was killed during
this season.
109Ibid.
HOjoe L. Herring, "Black Bear in Louisiana" .(Louisiana Wild
Life and Fisheries Commission Wildlife Education Bulletin No. 22,
Louisiana Wild Life and Fisheries Commission, New Orleans, Louisiana,
1962).
72
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Wild Turkey (Meleagris gallopavo)
Wild turkeys have been introduced into the basin in Pointe
Coupee and Iberville Parishes. The turkey population in Pointe Coupee
Parish has increased to the point where hunting is allowed. The
highest ridges in the basin may have originally supported a few
turkeys, but early authors, cited by St. Amant, concluded that turkeys
were originally rare or absent in cypress-tupelo swamp areas.111
Bobwhite (Colinus virginianus)
Bobwhites are generally considered upland game birds, and in
Louisiana mpst are found on farmlands, cut-over pine lands, and sparse
longleaf pine woods.11? In the Atchafalaya Basin, most bobwhites are
found on farmlands in the northern basin and on either side of the
floodway. Huntable numbers of bobwhites occur only in the farmlands
where they are sought by a limited number of hunters with bird dogs.113
Foxes (Vulpes fulva and Urocyon cinereoargenteus)
Fox hunting is a minor sport in Louisiana, and most foxes are
probably killed by hunters seeking other game. Both species are
widely distributed in the state and are perhaps most abundant in up-
land areas in mixed pine-hardwoods with interspersed clearings.114
Foxes also occur in the vicinity of farmlands in alluvial bottomland
areas, and it is in these areas where they are perhaps most common
in the Atchafalaya Basin. Foxes are also trapped for their pelts,
but usually only a small number of pelts are taken. Food items
eaten by foxes include small mammals,such as rats, mice, and rabbits,
and some vegetable material.
Raccoons (Procyon lotor)
Raccoons are one of the major furbearers in the basin, and they
are pursued to a limited extent as a game animal. Most coon hunting
is done at night with dogs. In this form, it is limited mostly to
11]-St. Amant, 1959, op_. cit.
113Needs and Goals Sub-Committee, 1973, op_. cit.
^Lowery, 1974a, op. cit.
73
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higher land areas in the northern part of the basin. Raccoons are
also killed in the lower basin incidental to other types of hunting.
Some of the raccoon pelts taken in the basin are from animals
which were shot rather than trapped.
Opossums (Didelphis virginiana)
The lowly opossum is probably a more important game animal than
is usually realized, and it may be an important supplementary food
item for many low-income families. The opossum is abundant in the
basin and is rather easily taken. It is also trapped for its fur.
Bobcats (Lynx rufus)
Bobcats are present in all heavily wooded areas of the Atchafalaya
Basin in "appreciable numbers."115 They are hunted as a trophy animal,
but the sport is of a relatively minor nature. Bobcats occupy a high
position in the trophic structure of the terrestrial component of
the basin ecosystem. They have few predators other than man, although
occasionally a kitten may succumb to an owl or a hawk. Rabbits, mice,
and rats make up a large portion of the bobcat's diet. Predation by
bobcats on deer—mostly fawns—is only of minor occurrence, and most
deer eaten by bobcats are believed to be carrion.
Snipe (Capella gallinago)
The common snipe is a winter resident mostly in the marshes of
south Louisiana, including the marsh area of the Atchafalaya Basin.
Snipe also occur around lake shores and grassy fields in more northerly
areas. These birds are similar to woodcocks in their habits, except
for their greater utilization of the marsh and their tendency to be
somewhat more active in the daytime. Hunting for snipe takes place
mostly in the marshes of the lower basin.
Rails (Rallus elegans and Rallus longirostris)
The king rail (Rallus elegans) and the clapper rail (Rallus
longirostris). like snipe, are inhabitants of marshes, but are year-
round residents. The king rail prefers fresh marsh situations and
may be found also in wet fields and roadside ditches. The clapper
rail, however, is almost never found outside of brackish or saltwater
115Ibid.
74
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marshes. The Virginia rail (Rallus limicola) and the sora (Porzana
Carolina) are smaller game birds which are winter residents in the
marsh. The coastal marsh area is the major habitat for these birds
in the basin, and hunting for rails, which is undertaken by only a
few select sportsmen, is confined to the marsh. Most rails are
killed incidentally by duck hunters.
Bullfrogs
Bullfrogs (Rana catesbeiana) are sought both commercially and
for sport in the Atchafalaya Basin. The pigfrog (Rana grylio), which
is not as abundant nor as widespread as the bullfrog, probably makes
up a minor portion of the catch. Reported catches during the 1963-1973
period indicate an average of about 32,000 pounds per year coming out
of the basin.116 According to Comeaux, most frogs are caught shortly
after the season opens, although some frogging continues throughout
the year, except during April and May, when the season is closed.117
General Comments Concerning Game Animals
Although presently all of the Atchafalaya Basin serves as a
valuable habitat for game animals, the northern portion of the basin,
forested by tree species which are somewhat more adapted to higher or
better-drained lands, or sufficiently high or well-drained enough to
allow cultivation, appears to be best-suited to most game species.
The presence of many mast-bearing trees and the larger area of land
which is not subject to flooding are factors which increase the value
of the upper basin as a deer and squirrel habitat. Bears also rely
heavily on mast for food.
Floods limit the development of a deer population by driving the
animals to the highest available lands,where severe competition for
available foods may lead to starvation. Deer stranded by floods are
also subject to outbreaks of disease and are vulnerable to illegal
hunting. It was only through the concerned efforts of personnel of
the Louisiana Wild Life and Fisheries Commission, the United States
Army Corps of Engineers, and private citizens during the 1973 flood
when the Morganza Spillway was opened that widespread mortality among
the deer herd was avoided.
0. Allen, National Marine Fisheries Service, New Orleans,
personal communication.
Malcolm L. Comeaux, "Atchafalaya Swamp Life, Settlement
and Folk Occupations," in Geoscience and Man, ed. Bob F. Perkins
(Volume II, Baton Rouge, Louisiana: School of Geoscience, Louisiana
State University, 1972), p. i-xiv, 1-111.
75
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Such species as cottontail rabbits, doves, and quail most often
inhabit and develop highest populations in cleared or relatively open
areas—so much so that they have been classified as "farm game by
St. Amant in a wildlife inventory of Louisiana.110 Woodcock depend
heavily on cleared areas for feeding, and foxes are usually most
abundant in the vicinity of cleared land. Areas suitable for farming
in the Atchafalaya Basin occur in the upper basin and in protected
areas outside of the floodway.
Turkeys were probably originally distributed over most of the
upland areas of the state and on the broad and high natural levees of
major rivers. St. Amant does not consider the Lower Mississippi al-
luvial plain as an area which can be successfully managed for tur-
keys. H9 The stocking of turkeys into areas of Pointe Coupee and
Iberville Parishes takes advantage of the somewhat higher land in
these areas and its protection from flooding. Flooding during the
nesting season may destroy turkey eggs or young or prevent nesting,
as probably occurred to some extent during the 1973 flood.
Thus, it appears that many terrestrial game species in the
Atchafalaya Basin are best suited to relatively drier habitats—dry
enough to support abundant mast-bearing trees or, for farm game, to
allow clearing for cultivation. Flood control measures in the basin
which would cause drainage of backswamp areas, although having
drastic effects on aquatic and aquatic-related resources, would also
initiate a succession towards vegetation more characteristic of drier
areas and have beneficial effects on terrestrial game species.
Other Wildlife
The other wildlife120 of the Atchafalaya Basin includes a myriad
of invertebrates, fishes, amphibians, reptiles, mammals, and birds.
Time and space do not permit a detailed discussion of these forms, but
their importance should not be overlooked. These species are the
basic structural and functional elements of the swamp ecosystem,
whereas game animals, game and commercial fishes, and waterfowl are
only its more visible or usable components.
118St. Amant, 1959, op_. cit.
12°For convenience, the word "wildlife," which usually refers
to vertebrate animals exclusive of fishes, is expanded in meaning
here to include invertebrates and fishes.
76
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Invertebrates
Invertebrates are perhaps the most important animal group in
the basin. Including such diverse forms as protozoans, sponges,
coelenterates, flatworms, rotifers, nematodes, bryozoans, oligochaetes,
arthropods, and mollusks, invertebrates are a vast source of food for
vertebrate animals as well as other invertebrates. The numbers and
diversity of invertebrates, their diverse food and feeding habits,
larval stages, and habitats contribute greatly to the stability of
Atchafalaya Basin ecosystems.
Fishes
Besides game and commercial fishes, the waters of the area are
habitats for numerous other fishes which have no sporting or com-
mercial value. Of 77 species caught by Bryan et^ _§JL., 47 were non-
game or non-commercial species.121 Included in this category are
such small fishes as minnows, Copminnows, . silversides, darters, and
small sunfishes. Bryan et^ a!L. found mosquitofish (Gambusia affinis) .
silversides (Menidia spp.), bullhead minnows (Pimephales vigilax)»
and silverband shinners (Notropis shumardi) to be most abundant and
most frequent in occurrence in seine collections taken in the basin.122
Most of the small fishes feed on small invertebrates, such as
insect larvae, cladocerans, and amphipods, and are themselves food for
larger fishes, wading birds, and other animals.
Amphibians
At least six species of salamanders and thirteen species of frogs
and toads occur within the basin.123 Among the salamanders, two spe-
cies, the central newt (Notophthalmus viridescens) and the congo eel
(Amphiuma tridactylum)t are fairly common. The central newt, an aquatic
species, can often be seen swimming along the edges of bayous where it
forages for small crustaceans and insects. These newts are undoubtedly
eaten by many predator fishes. The congo eel usually lives in holes or
dens in the bottom mud of swampsiwhere it lays in wait of such prey as
crawfishes, small finfishes, or frogs.
et_ al., 1974, op. cit.
122ibid.
123U.S. Department of the Interior, 1974, op_. cit.
77
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Frogs and toads and their tadpoles are utilized as foods by a num-
ber,, of basin inhabitants including predator fishes, congo eels, snakes,
wading birds and kingfishers, minks, otters, and man. The bullfrog
(Rana catesbeiana) and the pigfrog (Rana grylio) are commercial spe-
cies. Frogs and toads of all kinds feed heavily on insects, and the
more aquatic forms feed also on crawfishes and small fishes. Frogs
feed on many insects which have aquatic larval stages, furnishing
only one of many examples of energy links between the aquatic and
terrestrial environments.
Reptiles
Reptiles definitely occurring in the Atchafalaya Basin include
the American alligator, twelve species of turtles, four species of
lizards, and twenty species of snakes.12^ Most of the reptiles oc-
curring in the basin are aquatic forms.
The American alligator (Alligator mississippiensis), currently
listed as an endangered species, occurs within the floodway portion
of the Atchafalaya Basin in "extremely low" numbers.125 They are
probably more numerous in the fresh marsh areas in the lower basin
below Morgan City. Alligators are generally responding to protection
and increasing in numbers in the coastal marshes and swamps in south-
eastern Louisiana. Nichols attributes low numbers of alligators in
the basin to illegal hunting activities,izb but it is also possible
that highly fluctuating water levels in the basin have inhibited re-
productive success of alligators by flooding of nests.
Chabreck conducted food habit studies of young alligators
(average total length = 1.06m in freshwater areas and 1.16m in saline
areas) living in fresh and brackish water marshes on the Rockefeller
Wildlife Refuge in southwestern Louisiana.127 Reported food items in-
clude insects, crawfish, grass shrimp, spiders, birds, snakes, and
fish in the freshwater areas, and insects, crawfish, blue crabs, fid-
dler crabs, and fish in the brackish water areas. Fur-trappers in
the marsh complain of alligators preying upon tnuskrats and nutria.
Adult alligators, in turn, have few predators (other than man);
124ibid.
125Nichols, 1973, op. cit.
127Robert H. Chabreck, The Foods and Feeding Habits of Alligators
from Fresh and Saline Environments in Louisiana (Proceedings, 25th
Annual Conference of the Southeastern Association of Game and Fish
Commissioners, 1971).
78
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however, alligator eggs and newly hatched alligators are preyed upon
by raccoons!28 and possibly other carnivores.
The sight of painted turtles basking in the sun on emergent
logs is a familiar one in the Atchafalaya Basin. At least 12
species of turtles occur here,129 and several species are gathered
as food by local residents. All of the turtles in the basin, except
for the Gulf Coast box turtle (Terrapene Carolina), which will seek
wet places during hot, dry weather, are aquatic. They are not highly
selective in their feeding habits and eat both animal and plant matter.
Snails and other mollusks, insects and insect larvae, and crawfish are
taken by most turtles. Dead animals, mostly fish, are also eaten.
Painted turtles and map turtles are more herbivorous than other spe-
cies, while snapping turtles, stinkpots, mud turtles, and soft-shelled
turtles are more carnivorous. Box turtles feed on mushrooms, insects,
snails, myriapods, dead animals, blackberries, and other fruits.!30
These animals come ashore to lay their eggs in holes dug in the soil.
Turtle eggs and young are subject to predation by roving mammals,
and small turtles in the water are eaten by predator fishes, snakes,
and birds.
Only four lizard species, the green anole (Anolis carolinensis)
and three skinks, are known to definitely occur in the floodway por-
tions of the basin.131 Other species are likely to be found, partic-
ularly on the higher ridges surrounding the area. Lizards feed al-
most exclusively on insects and are, in turn, preyed upon by snakes,
birds, and small mammals.
At least 20 species of snakes occur within the Atchafalaya
Floodway.132 Water snakes (genus Najtrix) , particularly, are abundant
and quite conspicuous. Three species of poisonous snakes, the southern
copperhead (Agkistrodon contortrix), the western cottonmouth (Ag-
kietrodonpiscivorous), and the canebrake rattlesnake (Crotalus hor-
ridus), are definitely known to occur in the basin; two others, the
Texas coral snake (Micrurus fulvius) and the western pigmy rattle-
snake (Sistrurus miliarius), are found in near-basin localities and
are suspected to occur inside the basin. The western cottonmouth is
128joanen, 1969, op. cit.
129U.S. Department of the Interior, 1974, op. cit.
130Clifford H. Pope, Turtles of the United States and Canada
(Volume 28; New York: A. A. Knopf, 1939), 343 p.
1 ^1
••••"•U.S. Department of the Interior, 1974, op_. cit.
132
Ibid.
79
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abundant in the basin, although it is often confused with the diamond-
backed water snake (Natrix rhombifera), and its numbers are sometimes
exaggerated. Snakes are carnivorous and, according to their habits,
feed on a variety of organisms. Aquatic forms feed on fishes, craw-
fishes, congo eels, salamanders, and frogs, while more terrestrial
forms feed on earthworms, insects, snails, toads, lizards, other
snakes, small mammals, and birds. Predators on snakes include man,
skunks, raccoons, bears, feral hogs, shrews, wading birds, owls,
hawks, predacious fishes, alligators, turtles, and other snakes.
Birds
The bird life of the Atchafalaya Basin is conspicuous and quite
diverse. A survey of authoritative texts on the birds of Louisiana
indicates that approximately 140-150 species of birds (including
waterfowl and other game birds), representing 17 orders and at least
42 families, may be expected to occur in the Atchafalaya Basin either
as permanent or seasonal residents or visitors.J-^.i-" Such a
diversity of species is not surprising in view of the location of the
basin at the southern terminus of a major migration route and the
numbers of different habitats for birds. These include farmlands
and towns, bottomland hardwood forests and wooded swamps, open water
lakes, bayous, and rivers, fresh, brackish, and salt marshes, and
beaches, all of which may be found in the natural Atchafalaya Basin.
Many of the birds in the basin are characteristic inhabitants
of wetlands. They are dependent, to a great extent, on aquatic or-
ganisms, such as aquatic plants, fishes, crawfishes, grass shrimp,
snails, and insects (either adult aquatic insects or insects with
aquatic larvae) as a food source and are thus directly linked through
133A. H. Wright and A. A. Wright, Handbook of Snakes of the
United States and Canada (Ithaca, New York: Comstock Publishing
Associates, 1957).
134ceorge H. Lowery, Louisiana Birds (3d ed.; Volume 30,
published for the Louisiana Wild Life and Fisheries Commission by
Louisiana State University Press, Baton Rouge, Louisiana, 1974b),
651 p.
135Harry C. Oberholser, The Bird Life of Louisiana (Volume 12,
published in cooperation with the Biological Survey, United States
Department of Agriculture, by the Department of Conservation, New
Orleans, Louisiana, 1938), 834 p. '
80
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food chains to the aquatic environment. Any change in the aquatic en-
vironment which would reduce its area or decrease its productivity
would cause a severe impact on many more-or-less terrestrial animals,
such as birds, which are dependent upon aquatic productivity.
Mammals
The known or presumed range of A3 species of mammals includes
all or part of the Atchafalaya Basin.136 The list includes familiar
species, such as the opossum, the armadillo, rabbits, squirrels, rac-
coons, and deer, and also such little-known or surprising forms as
bats, mice, rats, and black bears. Important furbearing mammals in
the basin include the nutria, muskrat, raccoon, mink, and others
(see section of this report on furbearers). Game species of mammals
are discussed elsewhere in this report.
Although many of the mammal species in the basin are aquatic or
are otherwise adapted to withstand flooded conditions, certain ground-
dwelling species, such as shrews, rats,.and mice, appear to be limited
in their distribution to the highest land areas. Even among more or
less aquatic species, such as the muskrat, floods may drown houses and
young. Slowly rising waters, which allow ample time to seek refuge,
do less damage than sudden massive floods,such as occurred when the
Morganza Floodway was opened in 1973. Small mammal populations in
the floodway have probably not yet recovered from the effects of this
flood.
Species such as the opossum, shrews, the cottontail rabbit,
harvest mice, and the cotton rat most often inhabit grassy fields or
forest edges near agricultural or other cleared areas. Pests, such
as the roof rat, Norway rat, and the house mouse do not only occur
in houses, barns, and other outbuildings, but also in grassy fields
and drainage ditches. They are consumed by such predators as hawks,
owls, and bobcats, and thus have integrated into natural communities.
Coyotes and foxes usually inhabit upland areas and probably oc-
cur in the northern part of the basin in low numbers. The red fox
is probably an introduced species. The coyote has spread into
Louisiana from Texas since about 1950 and is now widespread in the
northern part of the state.137 Coyotes occur in limited numbers in
the area of the Atchafalaya Basin.
136Lowery, 1974a, o£. cit.
81
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Bears have been introduced into the upper basin. A few native
bears known to occur in the lower part and in the marshes south of
Morgan City in the early sixties may still occur there.
The American beaver has in the past several years spread from
more northerly parishes and extended its range into most of the
Atchafalaya Basin.138 The dam-building habits of beavers will likely
pose interesting problems in the implementation of a water management
program in the area.
Bats are important, although often overlooked, mammal species.
They often live in the attics of old or abandoned houses or barns,
but they (especially members of the genus Lasiurus) also may spend
the daytime hours in hollow trees or clinging to tree branches or
clumps of Spanish moss. Bats feed almost entirely on flying insects.
Mammals, like birds, have various food habits which range from
herb'vorous forms,such as harvest mice, rabbits, and deer, to in-
sect rorous forms (bats) and omnivores,such as opossums, armadillos,
and b^ars, to top carnivores,such as weasels, otters, and bobcats.
Mammals, and indeed all life forms in the basin, are intricately
linked in a many-intersticed web of food relationships.
138greg Linscorabe, personal communication (February, 1975),
82
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VI
THE LOWER ATCHAFALAYA BASIN
While some consideration has been given to the consequences of
the use of the Atchafalaya Basin as a floodway, most attention has
been concerned primarily with the swamp basin lying above the alluvial
ridges of Bayous Teche and Black. Below this ridge, a whole set of
different environmental conditions and processes must be reckoned with.
The future development of the Atchafalaya River delta will have im-
portant impact over a zone extending from western Terrebonne Parish
into Vermilion Parish, and numerous choices concerning a desirable
pattern of delta growth and dispersal of water and sediment throughout
this large area will need to be evaluated.
Terrebonne Marshes
In the western coastal segment of Terrebonne Parish, the marshes
show several major problems that are closely related to the Atchafalaya
River. In recent years, large areas of freshwater marshes formerly
dominated by species such as the grass Panicum hemitomon and other
herbaceous hydrophytes, such as Sagittaria falcata. have undergone
degeneration and subsequent replacement by shallow water bodies
(Figure 6-1). This process cannot be attributed with present know-
ledge to any single cause, but several contributing factors can be
identified.
1) High stages on the lower Atchafalaya River during the spring
tend to cause flooding over these marshes to levels that exceed the
levels to which the marshes were adjusted when the Atchafalaya was a
smaller river with lower stage variation.
2) Accumulation of sediment from the Atchafalaya River along
the western edge of the Terrebonne marshes has partially impounded
drainage from the inner marsh areas.
3) Numerous rig location canals and oil and gas pipeline canals
have been excavated in the past three to four decades, leading to
greater access of floodwater into the area and deeper flooding. Spoil
banks from such canals have created severe impoundment over large
areas. This same network leads to greater drainage during the low
river stage in the dry season months,which exposes the highly organic
marsh soils to deterioration through biological oxidation, shrinkage,
and combustion from marsh fires, which are common. Thus, both
excessive flooding and overdrainage can be a problem .in the same area
at different times of the year.
4) Water hyacinth has risen to dominance over most of the af-
fected area, no doubt due to its indifference to flooded conditions.
The hyacinths form a dense mat which smothers pre-existing vegetation
when river stages fall.
83
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Figure 6-1. Extent of marsh replacement by shallow water bodies
(shaded areas) as determined by 1974 aerial photos.
84
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5) Natural subsidence, which is known to be occurring at about
1 m/century at nearby Eugene Island, must also be a factor in the marsh
breakup. Unnatural subsidence due to the extraction of oil and gas
from the several fields of the area is also likely to have contributed
to an unknown extent to the problem.
6) After destruction of the natural vegetative cover of the
marsh by any of several means suggested above, the organic soils may
be quickly broken up and removed by wave erosion, especially at times
when they are covered by water during storms.
The consequence of a continued rapid breakup of the marsh can be
anticipated at the present time only to a certain degree. A lake
should develop as the growing, shallow aquatic areas coalesce to greater
size. To some extent, sedimentation will counteract this tendency,
but it is not known at present if sedimentation will be of sufficient
importance to restore the marshes. A growing depression in this area
could lead to diversion of greater Atchafalaya River flow into the
area, eventually creating a deltaic distributary lobe which would re-
verse the tendency for land loss. With the creation of the Chene-
Boeuf-Black navigation channel, this process would be accelerated
since greater amounts of Atchafalaya River water will enter via the
enlarged channel. If the Chene-Bouef-Black navigation channel is not
constructed, then it might be possible to correct the problem of these
deteriorating marshlands by controlled introduction of water and sedi-
ment through a smaller channel.
Another important problem in western Terrebonne Parish is that
of drainage of water from the Lake Verret - Lake Palourde catchment
basin. During times of high stage in the Lower Atchafalaya River,
this water does not have an efficient outlet, but must escape by
overland flow across the marshes or via a circuitous route along the
Gulf Intracoastal Waterway (GIWW) and intersecting bayous and chan-
nels. Such flow is contributory to the problems of deteriorating
marshes. More information on the routing of these waters will be re-
quired in order to suggest a strategy for alleviation of this situation.
The decline of oyster production in western Terrebonne Parish is
also related to Atchafalaya River discharge, especially in years of
large floods, such as 1973 and 1974. Formerly cultivated oyster beds
in the area of Point au Per and Four League Bay are.no longer useable
because of both excessive mortalities from low salinities and high
turbidities and because they are condemned due to excessive coliform
counts from wastes carried by the river waters. In 1973-74, high
mortalities due to low salinities occurred as far eastward as Caillou
Lake. The value of the natural and managed oyster areas destroyed
by freshening is certainly great enough to justify efforts at remedy-
ing this situation. Caillou Lake has been estimated to yield 454.6
kilograms (kg) or 1,000 pounds (lbs)/acre of oyster meats when good
conditions prevail.
85
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A third problem in the western Terrebonne Parish area relates to
the GIWW and potentially to the Chene-Boeuf-Black Waterway if it is
constructed. The Chene-Boeuf-Black channels, even in their present
state, carry water in times of high Atchafalaya River stage to the
GIWW, by which it is carried eastward and distributed through various
intersecting channels. The sediment and water distributed in this way
may lead to future problems of channel maintenance.
Lastly, it should be said that the entire expanse of western
Terrebonne Parish represents a large, high quality fish and wildlife
habitat long used and valued by local inhabitants and persons from
other areas. Although it has already been subjected to much de-
structive use, it remains one of the largest and least disrupted marsh
habitat areas in Louisiana. It will undoubtedly suffer great and
rapid impact from the growth of the future Atchafalaya Delta and,
therefore, deserves comprehensive consideration in regard to its
problems and alternatives for management.
Atchafalaya Delta
Deltaic sedimentation has become an increasingly dominant process
in Atchafalaya Bay. Deposition of prodelta silty clays and clays has
been ongoing since the nineteenth century, increasing with Atchafalaya
River discharge and with gradual in-filling of the lakes north of the
Teche Ridge. Coarse-grained sedimentation was initiated in the 1950's,
and at present, bed—load sands are deposited at the mouths of VJax Lake
Outlet and the Lower Atchafalaya River, having resulted in a distinct
river-mouth bar at each channel. 9 Bottom topography of Atchafalaya
Bay has become subject to rapid changes with numerous islands emergent
during low tidal phases. Within much of the bay near the Lower Atcha-
falaya River mouth, water depths have been reduced to 0.3 m (1 ft).
Cratzley shows that depths are less than 1.8 m (6 ft) throughout
Atchafalaya Bay.1*" With deposition rates of as much as 0.1 m (0.3 ft)
annually, the open-water expanse will soon be replaced by an emergent
delta surface extending to the outer oyster reefs between Point au
Fer and Marsh Island. Predictions are for the presence of about 777
km2 (300 mi2) of new land by the year 2020.141
11Q
AJ:;D.W. Cratzley, Recent Deltaic Sedimentation, Atehafalaya Bay.
Louisiana (M.S. Thesis, Louisiana State University, 1975), 142 p.
I40lbid.
•*R.J. Shlemon, "Development of the Atchafalaya Delta,
Louisiana" (Report No. 13, Hydrologic and Geologic Studies of Coastal
Louisiana, Center for Wetland Resources, Louisiana State University,
1972), 51 p.
86
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Associated with delta progradation, adjacent areas are and will
be further affected. Initially, decreased depth and associated in-
creased turbidity due to wave motion will allow greater sediment
transport into adjacent areas due to wave-, tide-, and wind-generated
currents. In particular, the generally westward water movement must
be expected to contribute to a further reduction in depth of the ad-
jacent Cote Blanche Bay system. Subsequent delta development,
especially that of distinct distributary channels and associated
natural levees, will likely reverse present effects on Terrebonne
marshes and the Cote Blanche Bays for some time. With development of
natural levees and increasing dominance of overbank flow processes
deposition of coarse fractions will become more localized along levee
ridges while inter-levee areas become more protected, entrapping the
finer, suspended materials. Also, confinement of most sediment
transport to the distributary channels will ensure further seaward
movement prior to dispersal. Thus, adjacent areas may eventually be-
come bypassed by deltaic sedimentation for some time. However, such
change must also be viewed as temporary since development of additional
delta lobes through development of new distributaries may occur in a
westward and/or eastward direction,as shown by historic developments
of the Mississippi River delta. 2
Requirements with regard to management of the emerging Atchafalaya
Delta relate to the following subjects: flood control, navigation and
environmental quality. With regard to navigation, the requirement was
previously stated as the need to separate the navigation route from the
area of active delta building.
Concerning flood control, it should be pointed out that the de-
veloping delta becomes, in essence, an extension of the Atchafalaya
Floodway through which water must be routed to the Gulf. This will
require management of distributary channel development to ensure maxi-
mum hydraulic efficiency of the delta.
Environmental quality considerations concern primarily the ad-
jacent areas of Cote Blanche Bay and the Terrebonne marshes. In neither
case is there sufficient information on present conditions and trends
available to warrant specific recommendations. Options for management
of the Terrebonne marshes range from increased freshwater and sediment
input to a return to a more saline environment with possibly high pro-
ductivity. Further consideration should also be given to the pos-
sibility of managed changes in location of delta development.
142S. M. Gagliano and J. L. van Beek, "Geologic and.Geomorphic
Aspects of Deltaic Processes: Mississippi Delta System" (Report No 1
Hydrologic and Geologic Studies _of_ Coastal LoiHs-fpn^ Center for Wet- '
land Resources, Louisiana State University, 1<) 70), p. 140.
87
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A possible long-term delta management strategy is suggested by
the natural delta cycle as registered by Louisiana's recent geologic
history.143 Prior to artificial fixation of the Mississippi River
course in its present location, building and deterioration of delta
lobes were concomittant processes associated with which were cycles
of biological productivity related to the state of a particular delta
lobe. Were natural processes to run their course, the western Terre-
bonne marshes, as part of the Lafourche delta lobe, must be expected
to gradually open up into an estuarine system in which a length in-
crease in land-water interface would increase productivity. This
would be followed by an open-bay phase with decreasing productivity.
At that time, possibly some one to two hundred years from present,
the locus of delta growth may be forced through management toward
the Terrebonne area to initiate a new cycle of deltaic evolution.
Simultaneously, this would initiate the change toward a more saline
and biologically productive system in the then fully developed
Atchafalaya Delta. Management could thus be for alternate growth
and deterioration in the two adjacent areas of Atchafalaya Bay and
western Terrebonne.
1/>3S. M. Gagliano .et _al. , "Environmental Atlas and Multiuse
Management'Plan for South-Central Louisiana" (Report No. 18, Volume 1,
Hydrologic and Geologic Studies of Castal Louisiana, Center for Wet-
land Resources, Louisiana State University, 1973), 132 p.
88
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VII
BASIN HYDROGRAPHY AND HYDROLOGY
The key variables with regard to management options in the Atcha-
falaya Basin are surface elevation and water level. Taking into con-
sideration their areal and temporal variation, these two variables are
also the principal controls over fish and wildlife habitat and deter-
mine land use suitability for agricultural, urban, and industrial
development. Water level, however, is only one aspect of basin hydro-
graphy. Additional consideration needs to be given to the source of
water, its availability, and the manner in which its movement through
the system is controlled.
Verret and Fausse Point Basins
Annual flooding and drainage are two factors that are highly
relevant as land use constraints in the Atchafalaya Basin. Prepared
by the United States Department of Agriculture (U.S.D.A.) Soil Con-
servation Service, Figure 7-1 shows the area flooded with a frequency
of 40£, or twice every five years, during the months of June through
November, excluding flood conditions generated by hurricanes or use
of the Atchafalaya Basin Floodway. Inspection of gaging data shows
that this distribution of the partial year is slightly conservative
for areas outside the floodway. For instance, the U.S.C.E. gage at
Pierre Part in the Verret Basin for the period of 1961 through 1972
reveals that highest stages occur in April, with an average of 0.63 m
(1.89 ft) mean sea level (MSL). Highest stages during the period of
June through November occur in September, when the average stage is
.0.45 m (1.63 ft) MSL.
South of the Teche and Black Ridges, the flooded lands include
the entire coastal area, with the exception of the natural levee ridges
along Bayou Cypremont and Bayou du Large and the artificially protected
ridge along Bayou Sale. Flooding of the coastal area has multiple
causes which may occur individually or in combination. Among these
are high Atchafalaya River discharges, local rainfall, and wind-
generated tides. The effect of high Atchafalaya River discharges
relates to the diversion of flow into channels ancillary to the Lower
Atchafalaya River and Wax Lake Outlet as referred to earlier.
In the Fausse Point and Verret Basins, flooded conditions are
seen to regularly prevail as far north as Interstate 10. The flood-
prone area in the Fausse Point Basin comprises the wetlands around
Lake Fausse Point, where the natural levee ridge of Bayou Teche is most
distant from the floodway-guide levee, so that a depression is formed.
Being the lowest part of the Fausse Point Basin, this depression col-
lects much of the local runoff from that basin. Surface runoff from
the extensively farmed Teche levee ridge is directed eastward toward
89
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¥/'* v/i»-••tt-xv. m'>=
'•^TJMili
Fr.qu.nc, Flood
Gog* R«odlnfli Prot«ci«d
(El.volloniMSL)
- - • ' .„ — ...-
— » .
1 .
40 MIU9 , ,
tl"'
Figure 7-1.
Areas where flood frequency equals or exceeds 40
percent during the period of June through Novem-
ber. 144, 145
144U.S. Department of Agriculture, Flood Frequency Contour
Map, Areas 3 and 4 (Soil Conservation Service, Alexandria, Louisiana,
1973) 2 maps.
145
U.S. Army Corps of Engineers, 1974, op_. £jLt
90
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the floodway-guide levee, where it is collected by the levee borrow-pit
and routed into Lake Fausse Point. Drainage from the Fausse Point
Basin is provided through the Charenton Drainage and Navigation Canal
into West Cote Blanche Bay. This condition makes water levels in the
Fausse Point Basin dependent on local runoff as well as water level in
the coastal area. Prolonged high tidal levels as a result of wind
set-up may greatly impede drainage. The same obstruction to drainage
may be caused by high river stages in Wax Lake Outlet and associated
diversion of flood water through the Intracoastal Waterway into the
Charenton Canal.
As illustrated by Figure 7-1, the flood-prone area in the verret
Basin to the east of the floodway is much more extensive; yet causes
of flooding are similar to those in the Fausse Point Basin. The nat-
ural levee ridges of the Mississippi River and Bayou Lafourche are
distant from the floodway-guide levee, leaving an extensive, north-
south oriented depression. Inherent to the natural levee slope, all
flow is directed toward this depression,which has only one major out-
let, Bayou Boeuf.
As is the case with the Fausse Point Basin, the Verret Basin
represents a distinct hydrographic unit, with water input entirely de-
pendent on local rainfall. Using the methods developed and described
in the previous study,1™ it is calculated that total annual runoff
generated within the Verret Basin is in the order of 1.335 x 10^ m3
(44.5 x 10° ftj). Runoff values are highest during February,when they
attain an average value of .273 x 10& m3 (9.1 x 10» ft3) and lowest '
during August,with an average value of 6000 m3 (0.2 x 106 ft3). The
overall slope of the basin directs water to the southwest toward the
eastern floodway-guide levee and into Lake Palourde.
With the natural levee ridges of Bayou Black blocking southward
disposal of runoff into the coastal wetlands, a major constraint is
placed on removal of water from the area. Based on inspection of the
basin s drainage network, it is estimated that 80% of the total runoff
leaves the basin through Bayou Boeuf, which crosses the Bayou Black
ridge and connects Lake Palourde with Bayou Chene. The remaining
runoff escapes through a number of drainage canals connecting the
southeastern part of the Verret Basin with Bayou Black.
As a result of Bayou Chene, and consequently Bayous Boeuf and
Black, being linked with the Lower Atchafalaya River, high Atchafalaya
River discharges are associated with diversion of water into Bayou
Chene and severely impede drainage from the Verret Basin. Such di-
version has been found to occur 60% of the time.147 High tidal levels
in the coastal area have a similar effect. Under a combination of the
146Coastal Environments, Inc., 1974a, op_. cit.
147
U. S. Army Corps of Engineers, 1974, op. cit,
91
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above circumstances, flow in Bayou Boeuf may even be reversed, with ad-
ditional water entering Lake Palourde from the south and further raising
backwater flooding stages.
For both the Fausse Point and Verret Basins, it becomes apparent
that flood frequency and drainage constraints form a major limiting
factor with regard to land-use options. Well-drained lands are co-
incident only with the major natural levee ridges of Bayou Teche, the
Mississippi River, and Bayou Lafourche, along the margin of the basins,
and along some additional older levee ridges within the upper Verret
Basin north of Interstate 10. Marginally drained areas are found in
the flood plains in the upper Verret Basin and along the smaller
natural levees of the old Mississippi River or Lafourche distributaries
or crevasse channels, such as Bayou Pierre Part, Little Bayou Black, and
Bayou Black. Still, in many of the above areas, drainage remains pro-
blematic, particularly along the levee margins, where surface gradients
are extremely low and surface-water removal is slow. For this reason,
watershed protection and flood-prevention work have been planned in
both basins by the U.S.D.A., Soil Conservation Service. In the Verret
Basin, this work calls for a two-year level of protection for crops and
pasture through realignment and modification of 230 miles of stream
channels. These channels will provide a more rapid and direct drainage
of surface water from the developed levee ridges into one or more major
channels traversing adjacent wetlands and discharging into Lake Verret
and Lake Palourde. Similarly, 256 miles of stream-channel realignment
and modification are planned in the Fausse Point Basin.
Atchafalaya Basin Floodway
In the Atchafalaya Basin Floodway, flooding is in the first place
related to Atchafalaya discharge, which attains highest values during
the spring months. During normal high stages, nearly the entire area
south of U.S. 90 is flooded. Overflow conditions occur in much of the
area even during the dry and low months as shown in Figure 7-1. Two
flooding processes are recognized in the floodway, the areas of which
are roughly divided by Interstate 10. This may be further illustrated
by Figure 7-2, which shows the movement of water during average high
Atchafalaya stages.
North of Interstate 10, flooding can generally'be-described aa hack-
water flooding. Atchafalaya River water diverted through Bayou La Rose
to the west and through the East Freshwater Diversion Channel to the
east is forced northward toward the West Atchafalaya Floodway and Mor-
ganza Floodway, respectively. To this is added local runoff from the
sizable watersheds represented by these f loodways and by the Point
Coupee area to the north of the Morganza Floodway.
92
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« - uPPli Bill!
I - usrun 1<
FBI'SM u«ir« omesinn CHAMI
1 - [AM IRISH WAUR D1VIRSIOH
« • UIST AIUSS
•> l«',l AllISS f«'ili|| J
Figure 7-2. Diversion of Atchafalaya River flow into individual sub-
basins through channel flow (arrows) and overbank flow.
93
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To the south of Interstate 10, a totally different regime is pre-
sent. As discussed in a previous report,145 the topography of the Lower
Atchafalaya Floodway is comprised of a series of sub-basins arrayed on
either side of the Main Channel. The basins are separated from each
other by distributary channels and associated natural levee or levee-
spoil ridges. Spoil banks also separate each basin from the Main Chan-
nel. Under more natural-conditions, these basins were flooded through
annual overflow from the Atchafalaya River. During high stages, flood
water covered the entire width of the floodway, with the exception of
high natural levees and spoil banks. However, due to man s activi-
ties this exception has become highly significant. Banks along the
Main Channel and major distributaries have been raised by spoil to the
extent that flooding for average high stages has predominantly become
dependent on openings in the levee ridges that: surround individual sub-
basins.
Based on the mean annual maximum stages for the period of 1961
through 1970, topographic data obtained from the U.S.C.E. survey
ranges, aerial-photo interpretation, and field inspections, the na-
ture of flooding was determined for each of the sub-basins or manage-
ment units. Comparison of the mean high water level at each intersec-
tion of a survey range and Main Channel (or major distributary) with
bank-elevation allowed determination of the extent to which flooding
occurs as a result of true overbank flow. True overbank flow occurs
when water from a channel enters a sub-basin by overflowing the chan-
nel banks as opposed to being diverted from a channel into a sub-basin
through a stream connecting the two.
Inspection of Figure 7-2 reveals that the majority of the sub-
basins or management units are, on the average, not flooded through
overbank flow but through channel flow. The map shows, respectively,
banks not allowing overflow, banks allowing overflow, and major points
of channel flow input. Overbank flow from the Main Channel is pre-
vented in nearly all cases except along the lower margins of the Cre-
vasse and Upper Belle River Units. Overbank flow is also prevented
along most of the length of the distributaries, East and West Access
Channels, East and West Freshwater Diversion Channels, and Fausse Point
Cut-off.
Natural conditions have been maintained most closely in the
southeastern part of the floodway bounding the alternate Intracoastal
Waterway. Water diverted into the waterway by the eastern distribu-
taries annually overflows its banks into Flat Lake and Upper Belle
River. Bayou Pigeon, receiving flow from the Intracoastal Waterway,
also allows annual overflow. Additional overflow is possible through
backwater diverted from the Main Channel into Lake Cbicot, which also
serves the Crevasse unit.
148Coastal Environments, Inc., 1974b, op_.
94
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The remaining management units are seen to be flooded predomi-
nantly through channel flow provided for by secondary channels or min-
eral industry canals. In some cases, water is allowed to enter from
all sides, such as in Pigeon Bay. In other cases, such as in the manage-
ment units to the west of the Main Channel, flooding is largely a back-
water process, with water entering mainly from the side or lower end.
Conditions where flooding is mainly dependent on diversion of
water from a major sediment-carrying channel through channel flow are
highly undesirable, as illustrated by Buffalo Cove Management Unit.1^
Water enters the sub-basin at a high velocity and for some distance
carries a substantial volume of sediment, which is eventually deposited
in the swamp interior as water disperses. Inherently, intensity of
this process is inversely proportional to the number of channels serv-
ing a particular sub-basin.
The above conditions stand in strong contrast to overbank flood-
ing, where flow velocities decrease immediately adjacent to the water-
supplying channel, and sediment is deposited on the channel banks.
Thus, channel flow tends to equalize elevations by filling in the low
areas, whereas overbank flow tends to maintain the basin shape by ele-
vating the rim. Areas where overbank flooding is dominant, such as
Upper Belle River and Flat Lake, have experienced minimal increases in
elevation of the swamp floor. Sedimentation has occurred predominantly
along the southern margins, where the Main Channel is directly connected
with a number of lakes.
Where backwater flooding is the only process by which water en-
ters a swamp basin, it leads to diminished circulation or water re-
placement away from the point of water input. As illustrated by the
northern half of the Buffalo Cove Management Unit, insufficient circu-
lation results in water quality problems in areas where water is present
throughout the year. The above condition contrasts with those areas
such as Bayou Fordoche and upper Bayou des Glaises, which experience
backwater flooding, but have an open upper boundary where local runoff
provides an annual flushing effect.
The previous evaluation of flooding characteristics is partially
based on computation of water levels in the major channels throughout
the Lower Atchafalaya Eloodway. The first step in this computation is
a compilation of daily stages for the period of 1961'through 1970 for
all U.S.C.E. gaging stations. Location of these stations is shown in
Figure 7-3. Monthly averages for the ten-year period are then calcu-
lated for each gaging station utilizing relationships between proximate
gages to fill in data gaps where records are incomplete. A computer
program developed to determine water levels at intermediate points on
the basis of linear interpolation is then used. Intermediate points
include all U.S.C.E. range-line intersections and all major points of
149
A"Coastal Environments, Inc., 1974b, op. cit.
95
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/urvey Ronqe/
and
Gaqlnq /totlon/
ttceno
r'..'>i A^T.
V . > v • \\ v
•' \
______ fo_ ,'' ..... ^u;__
Figure 7-3.
Locations of U.S.C.E. topographic survey ranges and
stage gaging stations, and of data control points
used in calculation of sub-basin water levels,
<)„
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flow diversion. Figure 7-3 shows all points for which average monthly
mean water level has been determined. The following paragraphs util-
ize these 'data to further evaluate present and proposed (as related to
the Center Channel) hydrographic conditions in the swamp sub-basins of
the floodway.
Sub-Basin Hydrographs and Hydroperiods
Annual variations of water level are considered to be one of the
major contributing factors to productivity of the floodway swamps.
Changes regarding maximum and minimum variation are one of the concerns
related to the possible impact of proposed Center Channel dredging.
Monthly mean water levels as obtained through the previously described
program are therefore utilized in 1) estimating present extent and dur-
ation of flooding in the various sub-basins or management units, 2)
evaluation of the changes to be brought about by dredging of the Center
Channel, and 3) development of a possible hydrograph for water-manage-
ment purposes.
The first step is to relate channel stages obtained at the loca-
tions shown in Figure 7-3 to water levels representative of individual
sub-basins. In the absence of stage observations within the sub-basins
and within the constraints of available time, the best approximation
is considered to be a weighted combination of channel stages and chan-
nel locations, with weighting dependent on the location, nature, and
relative magnitude of flow from a channel into a sub-basin. Necessari-
ly, this method ignores water-surface slope within a sub-basin.
The second step is a compilation of data for proposed Center Chan-
nel conditions. To accomplish this dual rating, curves in terms of
Simmesport discharge were developed for all possible gaging stages util-
izing results from the U.S.C.'E. fixed-bed model study.1*0 These curves,
illustrated in Figure 7-4 for Upper Grand Lake, were used to adjust cal-
culated mean stages at the gaging stations of Figure 7-3 to future con-
ditions of the Main Channel. The adjusted data were then processed in
the same manner as the ten-year period data to obtain intermediate chan-
nel stages and sub-basin water levels.
As an example, the two obtained hydrographs, present and future,
are shown in Figure 7-5 for the Buffalo Cove Management Unit. The
hydrographs indicate that Center Channel construction would lower water
levels about two feet in late summer and early fall under normal con-
ditions, and about five feet during the spring season. Since stage
reductions along the Main Channel increase in an upstream direction,
most management units further upstream would experience a somewhat
greater reduction in water levels. Tables 7-1 and 7-2 summarize these
facts for each of the individual management units within the floodway.
150U. S. Army Corps of Engineers, 1974, op. cit.
97
-------
i8i—i 1 1 r
14
12
** 10
& •
CO
**
CO
.0
100
00
1000 cms
10
15
-I 10
3 «
.£
"«
Simmesport Discharge, 1000 cfs
Figure 7-4. Stage-discharge relationships at Upper Grapd Lake for condi-
tions at present and after proposed Center Channel dredging.
98
-------
vo
VO
9
O)
(0
*<
CO
"co
O
M
M
J J A
Months
Figure 7-5. Stage hydrographs of Buffalo Cove Management Unit as calculated for present and proposed Center
Channel conditions.
-------
Present and Future Averages of Water Levels, West Floodway.
January
Present
Future
Difference
February
Present
Future
Difference
March
Present
Future
Difference
April
Present
Future
Difference
May
Present
Future
Difference
June
Present
Future
Difference
July
Present
Future
Difference
August
Present
Future
Difference
September
Present
Future
Difference
October
Present
Future
Difference
November
Present
Future
Difference
December
Present
Future
Difference
Bayou
Fordoche
15.1
7.5
7.6
15.7
8.1
7.6
16.5
8.9
7.6
17.4
9.8
7.6
17.5
9.9
7.6
15.6
8.0
7.6
12.9
5.8
7.1
12.2
5.4
6.8
10.8
4.5
6.3
10.9
4.6
6.3
11.1
4.7
6.4
12.9
5.8
7.1
Present - Present mean monthly
Future - Future mean monthly
Cocodrie
Swamp
10.4
4.8
5.6
11.2
5.4
5.8
13.4
6.9
6.5
15.7
8.9
6.8
15.2
7.4
7.8
12.2
5.9
6.3
8.7
3.9
4.8
7.0
3.0
4.0
5.6
2.6
3.0
6.2
2.8
3.4
6.0
2.7
3.3
8.1
3.4
4.7
stage in feet
stage in feet
Beau
Bayou
8.5
4.8
3.7
9.3
5.4
3.9
11.8
7.4
4.4
14.4
9.8
4.6
13.6
9.2
4.4
10.6
6.4
4.2
7.1
4.0
3.1
5.3
2.8
2.5
4.2
2.5
1.7
5.0
2.8
2.2
4.6
2.7
1.9
6.7
3.4
3.3
above mean
above mean
Buffalo
Cove
6.4
3.0
3.4
6.8
3.7
3.1
8.7
5.0
3.7
10.7
6.5
4.2
10.3
6.1
4.2
8.0
4.5
3.5
5.4
2.6
2.8
4.2
2.1
2.1
3.5
1.8
1.7
4.0
2.1
1.9
3.7
2.0
1.7
5.0
1.3
3.7
sea level.
sea level.
100
-------
Table 7-2.
January
Present
Future
Difference
February
Present
Future
Difference
March
Present
Future
Difference
April
Present
Future
Difference
May
Present
Future
Difference
June
Present
Future
Difference
July
Present
Future
Difference
August
Present
Future
Difference
September
Present
Future
Difference
October
Present
Future
Difference
November
Present
Future
Difference
December
Present
Future
Difference
Bayou des
Glaises
7.7
3.7
4.0
8.7
4.2
4.5
11.5
6.4
5.1
14.4
9.4
5.0
13.5
8.8
4.7
10.8
5.8
5.0
6.8
3.2
3.6
5.0
2.4
2.6
4.0
2.0
2.0
4.8
2.3
2.5
4.0
2.0
2.0
6.0
3.2
2.8
Pigeon
Bay
7.4
4.1
3.3
8.1
4.6
3.5
10.4
6.3
4.1
12.6
8.8
3.8
11.9
8.0
3.9
9.4
5.4
4.0
6.2
3.4
2.8
4.7
2.6
2.1
3.8
2.2
1.6
4.4
2.5
1.9
4.0
2.4
1.6
5.8
3.1
2.7
Present - Present mean monthly stage in
Future - Future mean monthly stage in
Flat
Lake
5.0
2.9
3.1
5.4
3.2
?.?
7.1
4.3
2.8
8.8
5.8
3.0
8.3
5.3
3.0
6.5
3.8
?..7
4.3
2.6
1.7
3.3
2.0
1.3
2.8
1.8
1.0
3.2
2.0
1.?
2.8
1.8
1.0
3.9
2.3
1.6
feet
feet
The
Crevasse
2.8
2.0
0.8
3.2
2.2
1.0
4.2
3.1
1.1
5.5
4.2
1.3
5.2
4.0
1.2
4.1
3.0
1.1
2.8
2.2
0.6
2.2
1.8
0.4
2.0
1.7
0.3
2.0
1.6
0,4
1;8
1.4
0.4
2.2
1.8
0.4
above mean sea
above mean sea
Upper Belle
River
2.8
2.0
0.8
3.2
2.2
1.0
4.2
3.1
1.1
5.5
4.2
1.3
5.2
4.0
1.2
4.1
3.0
1.1
2.8
2.2
0.6
2.2
1.8
0.4
2.0
1.7
0.3
2.0
1.6
0.4
1.8
1.4
0.4
2.2
1.8
0.4
level .
level .
101
-------
In the previous report,•'••'I a method was developed to relate
water levels to area and depth flooded. Use was made of a hypsometric
or frequency-elevation curve; this is a curve that shows the percent-
age of area below a given elevation or water level. This method pre-
sently is utilized for further characterization of present and future
hydrographic conditions and determination of management requirements.
This characterization takes into consideration: 1) the area submerged,
2) the duration of submergence, and 3) the hydroperiod, which is a
major parameter with regard to habitat.
Five hydroperiod classes, or flood duration intervals, can be
distinguished when taking into consideration typical environments with
regard to plant species and uses by fish and wildlife types. These
classes, I-V, are presented in Table 7-3 and are related to specific
habitats in terms of flooding characteristics, plant communities, and
importance to fish and wildlife. The last row of the table for each
class states water and related management objectives believed to be
essential for maintaining the environmental quality within each of the
areas synonymous with a certain hydroperiod class.
Hydrologic characterization of management units within the flood-
way can now proceed for three conditions: 1) present, 2) resulting at
implementation of the proposed Center Channel, and 3) managed accord-
ing to the objectives stated in Table 7-3. The Pigeon Bay Management
Unit is utilized as an example and will be discussed in reference to
Figure 7-6. For all other management units, the hydrologic informa-
tion is depicted in an identical manner in Figures 7-7 through 7-14.
Present conditions in Pigeon Bay (Figure 7-6) are described by
the two curves giving absolute elevation of the land surface (Curve D)
and present average annual variation of water levels (Curve B). Using
the left-hand and bottom scales, the hypsometric curve (D) shows the
percentage of the total area that lies below a given elevation, or the
percentage of the total area that is flooded when water level attains
a given elevation. For example, the present average hydrograph (B)
shows maximum water level to occur in April at 4 m (13 ft) MSL. At
that level, 86% of the Pigeon Bay Management Unit will be flooded, as
indicated by the dashed line a - b - c.
In the above manner, it can also be determined what percentage
of the area is presently flooded for a given period of time; that is,
what percentage of the management unit experiences a given hydroperiod.
For example, to determine what percentage presently experiences a 4- to
8-month hydroperiod (Class III), horizontal lines equivalent to 4-
and 8-month periods, respectively, are fitted under the hydrograph (B).
In Figure 7-6, position of the line corresponding to the 4-month hydro-
period for present conditions is found using the right-hand scale (pre-
sent). The line segment d - e is equivalent to a 4-month period. Its
Environments, Inc., 1974a, op. cit.
102
-------
o
OJ
Hydroperiod
Class Interval
Flooding
Characteristics
Plant
Communities
Importance
to
Fish
and
Wildlife
Management
Objectives
Class 1
0-1 mot,
Permanent and subpermaneat aquatic
habitat; lakes, bayoua, main river
channel*.
Epiphytes of tree covered areas:
Spanish moss, lichens, mosses,
resurrection fern.
Overstory: water tupelo, baldcy-
preas; willow along river channels.
Underatory treea and ahruba:
buttonbuah.
Floating aquatic planta: water
hyacinth* water lettuce, frogblt,
duckweed. Rice la. Azolla.
Submerged aquatic plant*: coontal]
water celery, Efteria. fanvort,
Hydrllla. Chara.
Permanent habitat for fisSes and
other aquatic fauna. Lakes and
tayoua are spawning areas for sport
and commercial fishes. River
channel* provide habitat for fishes
preferring a current (channel
catfish, striped baas, paddleflsh).
!rawflsh population small as
ompared to swamp areas.
Habitat for minks, otters, nutria,
raccoons, wading birds, waterfowl,
snakes, alligators, frog*.
. Maintenance of aquatic area.
. Water quality protection and
enhancement.
. Reduction of sedimentation rate.
Control of aquatic weed*.
. Reduction of extreme flood
volume.
Class II
1-4 mom.
Swampland subject to extended
flooding. Flooding may begin in
November and last through July or
Later. Wholly or partly devatered
from late summer to early fall.
Deep awampa.
Epiphytes: Spanish moss, resaurac-
tlon fern, lichens, mosses.
Overatory tree*: water tupelo,
baldcypress.
Dnderstory treea and shrub*:
buttonbuah, water elm.
Herbaceous forms: Floating
aquatic* - water hyacinth, water
lettuce, duckweed, frogblt, Rlccla,
Azolla. Submerged aquatic -
coontall. Emergent aquatics -
arrow-arum, pickerclweed.
Alternately part of the aquatic and
terrestrial environment. Feeding
area for adult and juvenile fishes.
Long hydroperiod assures time for
growth of juvenile fishes.
Crawfish are expoaad to prolonged
predation.
tabitat for furbearers, wading
birds, some waterfowl.
May serve as habitat for terrestrial
species (deer, rabbits) when dry.
. Maintenance of a water depth of
at least 4 ft. during months of
crawfish trapping.
Improvement of oxygen content of
water* to reduce trap mortali-
ties to crawfish.
. Improvement of extent of
dewaterlng In late summer and
early fall.
. Reduction of sedimentation
. Reduction of extreme flood
volume.
. Control of aquatic weeds.
Class III
4- 8 mot.
Moderately flooded swampland.
Flooding may begin In December and
extend through July. Typically dry
old-summer to mid-fall.
Intermediate awampa.
Epiphyte*: Spanish moss, lichens,
mosses*, resurrection fern.
Overstory trees: baldcypress, wate
tupelo, pumpkin ash, green ash,
bitter pecan, black willow and sand
bar willow In areas where sediment a
tlon is active.
Understory trees and ahruba:
buttonbush, Virginia willow, silver
bells, water elm.
Herbaceous forms: Floating
aquatics - water hyacinth, water
lettuce, frogblt, duckweed, Riccia.
Azolla, Submerged aquatics - coon-
tall. Emergent aquatics - lizard's
tail, arrow-arum, spider lily,
arrowhead .
Intermediate hydroperiod swamps are
utilized as feeding areas by adult
fishes and are important as nursery
areas for young of year fishes.
Hydroperiod Is long enough to allow
for growth and sexual maturity of
crawfish and short enough to prevent
over-predation by aquatic predators:
crawfish burrow into bottom suds
luring dry periods.
intermediate hydroperiod swamps
serve as habitat for aquatic
mammals, birds, reptiles and
amphibians when flooded and for
terrestrial apecles when drained.
1. Regulation of hydroperiod to
assure adequate conditions for
crawfish and fish, reproduction.
. Reduction of sedimentation rate.
i. Control of aquatic weeds.
. Reduction of extreme flood
volume.
Class IV
8-11 MM.
Swampland subject to a relatively
short flood period. Land la usual 1
flooded only during the spring
months during highest river stages.
Shallow swamps.
Epiphytes: Spaniah moss, lichens,
•oases, ressurection fern.
Overstory: baldcypress, green ash,
red maple, bitter pecan; black
willow, cottonwood, and sycamore
may become established where
sedimentation is strong.
Understory trees and shrubs: wax
myrtle, palmetto, Crataegus Spp.,
•vamp privet, red bay.
Vines: rattan, pepper vine,
Tree he lospermum .
Herbaceous Forms: Floating
aquatics - water hyacinth, water
lettuce, frofiblt. duckweed. Riccia.
Azolla. Emergent aquatics -
Lizard's tall, Polygonum Spp.,
royal fern, false nettle.
Swamps serve ss a nursery area for
uvenlle fishes and as a feeding
area for adult fishes when flooded .
Shallow swamps may also serve as a
spawning area for certain fishes
e.g., gars, carp).
'rawflsh utilize short hydroperiod
swamps as feeding and growing areas.
tiliced by aquatic species of
wildlife when flooded and by
erres trial apecles when dry.
. Reduction of extreme flood
volume.
. Reduction of sedimentation rate
Class V
11 -12 mo*.
Land which is not flooded or only
briefly flooded during the average
water-year. Flood period, if any,
usually In mid-spring, crests of
natural levees and spoil banks.
Epiphytes: Spanish moss, lichens,
•oases, ressurection fern,
mistletoe.
Overstory trees: cottonwood, black
willow and sycamore where sediments-
oak, American elm, hackberry, sweet-
gum, nut tall oak; live oak on some
higher sites.
Dnderstory trees and shrubs: box
elder, deciduous holly, wax myrtle,
Crataegus Spp., Elderberry,
pokeveed.
Vines: poison ivy, rattan,
muscadine, eardrop vine. Smllax
Spp., dewberry, crossvlne, trumpet
creeper, Japanese honeysuckle.
Herbaceous forms: false nettle,
butterwaad, Spilsnthes, Oplismenu* ,
Essentially dry land environments,
these areas miy be utilized by
aquatic fauna, Including fishes and
waterfowl, during the brief flood
icrlod. Much of the northern end o
type in the early stages of
succession. Wildlife present
includes deer, bear, rabbits,
squirrels, bobcats, skunks,
armadillos, turkey, woodcocks and
•any non-game species. Certain of
the higher ridges and islands in th«
lower end of the basin support this
type of habitat.
1. Reduction of extreme flood
volume.
2. Reduction of sedimentation rate.
Table 7-3. Relationship between flooding characteristics and biological conditions and values.
-------
PIGEON BAY
Months
j
14-1
20
40 60
Percent Area Less Than
I I
O- 1 mths.
II 1-4
III 4-8
IV 8-11
V 11-12
o
ui
in
O
a.
CO
o
UJ
0 9
>
O
c
o
•o
o
6 'C
12
Figure 7-6. Flooding characteristics of Pigeon Bay Management Unit. Stage hydrograph curves show annual
water level changes for desirable managed (A), present (B), and proposed Center Channel (C)
conditions. Curve D gives cumulative frequency occurrence of elevations. Pie-graphs show
relative size of areas subject to given hydroperiod class (Table 7-3) under conditions A, B, C.
-------
O
Ut
BAYOU FORDOCHE
M
Months
j j
MANAGED
PRESENT
PROPOSED
28
24
20
-8
-6
CO
E
** 16-
0)
9
— 12-
(0
0)
8-
4-
O-»-0
-4
(A
0)
*rf
0)
20
40 60
Percent Area Less Than
80
100
! I i
UJ .
1 \
0 :
6
.
12 :
•
E <
u <
/>
u
E
1.
0
6
11
™
-
-
-
™
-
n
i.
£
I.
C
O
re
UJ
c
0)
O
•2
CO
'c
O
0 *
T3
g
6 Q.
O
10 ^,
I
Figure 7-7. Flooding characteristics of Bayou Fordoche Management Unit.
-------
COCODRIE SWAMP
Months
j j
1
MANAGED
A
-r
o
-i-
PRESENT
PROPOSED
28-1
24-
20-
•8
-2
0-*-0
20
40 60
Percent Area Less Than
80
100
! I '
<
z
<
z
Ul
12
12
O
**
(0
LU
C
Q)
O
^
O
c
o
&
o
12
Figure 7-8. Flooding characteristics of Cocodrie Swamp Management Unit.
-------
BEAU BAYOU
Months
j
14
12
10
(O
E
8
H
5
-3
.UJ
4-
2-
0-«-0
-4
I 0-1 mths.
II 1-4
III 4-8
IV 8-11
V 11-12
100
o
UJ
I
<
I
O
(0
UJ
0)
5
£
CO
"c
o
cc
a.
1
o
UJ
(/>
O
a.
O
oc
a.
1
Percent Area Less Than
Figure 7^a, Flooding Characteristics of Beau Bayou Management Unit.
-------
I-
o
co
BUFFALO COVE
M
Months
j j
1
MANAGED
T
T
PRESENT
12-
10-
tf>
E
*- 8
0
0)
(0
UJ
HYDROPERIOD
-1
J-o
20
40 60
Percent Area Less Than
I I
0
III
13
Z
I
Z
111
tc.
a.
(ft
O
a.
O
cc
a.
C
O
«rf
(0
UJ
c
o>
5
^
o
12
12
a>
a
6 2
TJ
12
Figure 7-10. Flooding Characteristics of Buffalo Cove Management Unit
-------
O
VO
BAYOU DES GLAISES
Months
j
—i
MANAGED
—r
PRESENT
PROPOSED
14-
12-
10-1
(A
S«i
(0
9
u]
4-
2-
0 J-
-4
HYDROPERIOD
I 0-1 mth*.
M 1-4
III 4-8
IV 8-11
V 11-12
-3
2
-2
-i
20
40 60
Percent Area Less Than
80
100
Figure 7-11. Flooding Characteristics of Bayou Des Glaises Management Unit.
o
z
2
12
1C
a.
12
O
a
O
tr
a
C
O
4-1
CO
^)
UJ
C
0)
o
co
£
"c
o
T3
O
aJ
a
o
12
-------
FLAT LAKE
1
MANAGED
M
T
Months
j
T T
PRESENT
PROPOSED
12-
10-
(0
E
*• 8
O
O
1.
1
UJ
HYDROPERIOD
(A
a>
*-<
"I
•1
o-«-o
1 I I
oc
a.
8
a
o
cc
a.
12
12
(0
jj)
Ul
C
0)
5
co
O
•o
O
I
6 2
•o
12
20
40 60
Percent Area Less Than
Figure 7-12, Flooding Characteristics of Flat Lake Management Unit.
-------
CREVASSE
MANAGED
Months
~i T-
PRESENT
0
T"
PROPOSED
0
h.
o
UJ
3 z 55
2 UJ O
5 10 0.
i iu o
2 OC DC
m
0 :
-
-
_
6
™
•
12
0
-
-
6 ~
-
2 i
a.
C
O
flB
>
UJ
C
>
o
2
(O
£
*^
C
0
Z
° 1
®
a.
0
•o
6 >•
X
2
100
Percent Area Less Than
Figure 7-13. Flooding Characteristics of Crevasse Management Unit.
-------
UPPER BELLE RIVER
M
-r
Months
j J
A
T~
MANAGED
PRESENT
PROPOSED
20
40 60
Percent Area Less Than
I I
z
3
12
in
iu
o
UJ
O
a.
O
cc
a.
12
o
**
CD
UJ
c
0
O
c
«*
c
o
0 I
<5
a
o
12
Figure 7-14. Flooding Characteristics of Upper Belle River Management Unit.
-------
position shows that 2.7 m (8.7 ft) MSL (left-hand scale) Is the eleva-
tion below which flooding occurs for four or more months. Using the
earlier-described procedure involving the hypsometric curve, it can
thus be seen that 54% of the management unit experiences submergence
for a period equal to, or in excess of, four months. Likewise, it is
determined that 21% experiences flooding during eight or more months.
Thus, it can be said that a four- to eight-month hydroperiod is ex-
perienced by 54 minus 21, or 33%,of the Pigeon Bay Management Unit
located between elevations of 2.7 m (8.7 ft) and 1.6 m (5.2 ft) MSL.
In the above-described manner, percent area is also determined
for the other four hydroperiod classes (I, II, IV, and V), after which
the information is summarized in Pie-graph B (Figure 7-6). Similarly
percentages are obtained for the desirable managed (A) and proposed '
Center Channel (C) conditions, respectively, and expressed in pie-graph
form.
Having obtained the area of each of the management units, per-
centages can be converted into actual areal dimensions. This informa-
tion is summarized for each of the management units and hydroperiod
classes in Table 7-4, The examined condition for Pigeon Bay related
to a hydroperiod of four to eight months under present conditions is
seen to apply to 52 km^. The area of the entire Lower Atchafalaya
Floodway presently experiencing such conditions is 541 km2 with the
largest occurrence in the Upper Belle River Unit. Center Channel con-
ditions are seen to decrease this area to 415 km2. Tabulated data
further show that managed conditions would favor the eight-month to
eleven-month hydroperiod.
So far, the third, or managed, condition as shown in Figure 7-6
has been ignored, insofar as it concerns criteria used to arrive at the
management hydrograph. The curve labeled "A" is a hydrograph that is
considered to represent desirable conditions from a point of view that
takes jointly into consideration fish and wildlife requirements, for-
estry requirements, and commercial fisheries requirements. Thus,
management objectives as applied in the present case are not weighted
toward a particular species, but toward management for diversified sub-
systems as they presently exist, with emphasis on the use of renewable
resources and abatement of present deterioration.
A number of steps were taken to arrive at the management hydro-
graph. The first step is related to the high water level. In this
regard, it should be pointed out that water level is in some way pro-
portional to sediment input. Raising water levels in a sub-basin
above a given stage requires input of sediment-laden river water
With overbank flooding largely prevented, influx of sediment-laden
water must be considered to have detrimental impact. It can, there-
fore, be reasoned that inflow and water level should not exceed the
minimum that will sustain, or preferably enhance, present natural re-
source values. From that vantage point, minimally required high water
113
-------
Table 7-4, Areas subject to given hydroperiod class (Table .7^3)-Within floodway-
onanagement units for managed, present, and proposed condtttons respectively
KM2 - HYDROPERIOD I
Managed
Present
Proposed
KM2 - HYDROPERIOD II
Managed
Present
Proposed
KM2 - HYDROPERIOD III
Managed
Present
Proposed
KM2 - HYDROPERIOD IV
Managed
Present
Proposed
KM2 - HYDROPERIOD V
Managed
Present
Proposed
Beau
Bayou
32
16
44
5
25
24
30
28
14
9
6
1
9
10
2
Cocodrie
Swamp
81
47
123
18
42
10
25
35
15
9
9
1
22
22
6
Bayou
tordoche
79
80
207
11
15
52
52
48
45
35
39
3
142
137
12
Bayou des
Glaises
86
84
196
67
88
53
79
70
5
9
8
1
18
9
4
Pigeon
Bay
41
29
76
24
40
48
2
26
26
16
1
12
16
2
Flat
Lake
18
9
30
6
15
39
41
38
82
86
33
9
30
86
21
U. Belle
River
13
10
25
15
21
87
228
160
179
118
65
84
123
241
122
Crevasse
35
37
66
34
35
L27
30
25
8
6
2
4
37
A3
37
uffalo
ove
44
34
102
15
34
74
73
85
41
76
27
1
28
56
18
Totals
429
346
869
195
315
414
608
541
415
374
205
105
421
620
224
-------
levels are determined for each management unit taking into consider-
ation their present topography and characteristics, requirements of
principal fish and wildlife species, and small boat requirements for
commercial and sport fisheries.
The second step relates to the low water level. The three prin-
cipal considerations are necessary dewatering as a crawfish production
requirement, providing surface exposure to the atmosphere to allow de-
cay of organic matter for water-quality enhancement, and the need to
maintain sufficient water depth over a large enough area to serve as
a collection basin for fishes dispersed throughout the flooded swamp
during preceding high-water stages. One guideline toward selection of
the minimum water level is the knick point at the lower end of the
hypsometric curve. The hypsometric curve segment to the left of this
point represents predominantly the area occupied by lakes, channels,
and canals within the sub-basin. As a minimum, this area needs to re-
main flooded. Based on examination of present conditions in a number
of management units, the area flooded at minimum stages should not be
less than 5% of the management unit area, while it is desirable to
maintain more.
A third step relates to the shape of the hydrograph within the
constraints of a minimum and maximum water-level. On the basis of
present conditions and fisheries requirements, water-level variation
should follow as closely as possible the present river-stage regime,
with a general rise beginning in November, a peak by March/April, and
a low water stage from September through October. However, where de-
sired maximum and minimum water levels deviate from present condi-
tions and more efficient utilization of local runoff is desirable to
minimize needed river water input, control is necessary over inflow
and outflow into and from the management units. Such controls affect
rates of water-level rise and fall and, therefore, shape of the hydro-
graph, to some extent.
A hydrograph for managed conditions in which inflow and outflow
were controlled was obtained for the Buffalo Cove Management Unit in
a previous study.152 Taking into account monthly precipitation sur-
pluses, desired maximum and minimum levels, storage volume of the unit
feasible size of the inlet and outlet channels, and monthly water levels
inside the sub-basin and in surrounding supply channels, resulting flow
rates and monthly water levels during the periods between maximum and
minimum stages were calculated. The hydrograph thus obtained is the one
shown and labeled A -in Figure 7-10. The hydrograph deviates from.ithe
present regime mainly during falling stage when water levels are higher
than at-present during July and August. This deviation relates mainly
to stage difference inside and outside the sub-basiri controlling the
rate of drainage. Increasing the size of the outlet channel reduces
this channel only slightly.
152 Coastal Environments, Inc., 1974b, pp. cit.
115
-------
Results of the above study were utilized in the present study
to define the general shape of the management hydrographs for all units
in terms of rate of flooding and dewatering. Within the constraints
of the determined maximum and minimum stages, the management hydro-
graphs in Figures 7-7 through 7-14 represent an approximation of water-
level change expected to prevail under managed conditions where sub-
basin inflow and outflow are controlled.
To further evaluate changes resulting from the three conditions —
managed, present, and proposed — maps can be prepared showing distri-
bution of the areas experiencing a specific hydroperiod interval. This
can be done on the basis of topography, having obtained the relation-
ship between elevation and hydroperiod through Figures 7-6 to 7-14.
As an example, such distributions were developed for the Pigeon Bay
Management Unit and are shown in Figures 7-15, 7-16, and 7-17. Com-
parison of the maps shows a close resemblance between managed and
present conditions. The main change is an increase in the area ex-
periencing up to a 1-month hydroperiod at the expense of the 1- to 4-
month hydroperiod area. A slight gain is registered relative to pre-
sent conditions for the area having a hydroperiod of 8 to 11 months.
Much more severe are the changes related to proposed Center Channel
conditions. Permanent water bodies are partially converted to the 8-
to 11-month hydroperiod. The entire area presently experiencing a
Class IV hydroperiod is reduced to 4 to 8 months. In general, one no-
tices for all areas a shift to the next lesser hydroperiod and a major
increase of the area flooded for one month or less.
Water Balance, Yield, and Storage
One prerequisite to determining water-management options for the
Atchafalaya.Basin, and in particular for the floodway swamp environ-
ments with or without the proposed Center Channel is an evaluation of
DOtential water supply. Previous sections dealt predominantly with the
AtchafalayrRiver as a variable water source. Through analysis of the
wate? balance, the present section attempts to evaluate precipitation
yield within the Atchafalaya Basin Floodway as a manageable resource.
It should be pointed out, however, that inherent to data and time lim-
itations, quantitative results presented here should be considered
approximate and subject to further refinements through use of more
advanced and time-consuming analysis.
The first step in the evaluation of water yield within the Atcha-
falava Basin is the determination of amounts of rainfall, evapotran-
spiration loss, soil storage, and runoff at various points in the
basin Data from the previous study 153 utilizing the Thornthwaite -
Mather water-balance method, were avaiable for this purpose. These
data are in two forms of computer printout. One form provides monthly
153coastal Environments, Inc., 1974a, O£. clt_.
116
-------
0-1 MONTHS
1-4 MONTHS
4-8 MONTHS
8-11 MONTHS
11-12 MONTHS
MANAGED
PIGEON BAY
Figure 7-15. Distribution and size of areas subject to given hydroperiod class
CTable 7-3) under managed conditions in Pigeon Bay Management Unit,
117
-------
0-1 MONTHS
1 - 4 MONTHS
4-8 MONTHS
8-11 MONTHS
11-12 MONTHS
PRESENT
PIGEON BAY
Figure 7-16. Distribution and size of areas subject to given hydroperiod class
(Table 7-3) under present conditions in Pigeon Bay Management Unit,
118
-------
0-1 MONTHS
illlllil 1-« MONTHS
4-8 MONTHS
8-11 MONTHS
11-12 MONTHS
CENTER CHANNEL
PIGEON BAY
Figure 7-17. Distribution and size of areas subject to given hydroperiod class
, Table 7-3) under proposed center channel conditions in Pigeon
Bay Management Unit.
119
-------
values from 1945 through 1968 of all elements of the water balance at
every long-period climatological station in or close to the basin.
The second form provides data for the same period of net gains or
losses of moisture over 10,000-foot square cells within the basin.
These latter calculations were based on fixed land-water ratios in
each cell determined by examination of topographic maps.
It was decided to use the station water-balance data for deriv-
ing water yield. Two factors were considered in this decision. One
was the discovery during a special study of the Buffalo Cove Manage-
ment Unit154 that water losses from a water hyacinth cover can greatly
exceed the potential evapotranspiration (PE) rate. Water hyacinths
abound in the Atchafalaya Basin Floodway, and it is necessary to make
separate evaluations of land evaporation, open water evaporation, and
evapotranspiration from surfaces covered by water hyacinth plants. As
in the previous study, open water and non-hyacinth-covered swamps are
grouped together and assumed to lose moisture at the PE rate.
The second factor involved in the choice of data is the variation
in water level of inundated areas. This matter has been discussed in
the previous section, but it should be pointed out that water levels
in the winter and spring and the associated increase in flooded land
surface during that period cause a corresponding increase in area-wide
evaporation loss. Therefore, use of a fixed land-water ratio, although
acceptable on a long-term basis, results in overestimates of water
yield during the winter and spring months and underestimates during
the remainder of the year.
The climatological stations used in the water-balance analysis
are the same as those utilized in the previous study.1" Records for
these stations were processed by computer to determine monthly values
of precipitation (P), potential evapotranspiration (PE), and precipi-
tation surplus over land areas (S); P-PE then represents moisture gain
over wetlands, and S represents moisture gain or runoff over the dry-
land portion of the area. A third component, moisture gain over that
portion of the area covered by water hyacinths, remains to be deter-
mined .
There is evidence of abnormally high water losses in areas of
large concentrations of water hyacinths, such as the Buffalo Cove unit.
However, the only quantitative data bearing on this problem are a
series of lysimeter measurements in the Gulf coastal region made by
Penfound and Earle in June and July, 1946,15b and by Timmer and Weldon
154Ibid.
155Ibid.
156Penfound and Earle, 1948, op_. cit.
120
-------
from April to September, 1967.157 The measured evapotranspiration
from water hyacinths in these experiments is plotted against PE com-
puted from meteorological records in Figure 7-18. There is a wide
scatter of points in the graph, probably due to factors such as wind,
humidity, and cloudiness,not taken into account in the Thornthwaite
formula. However, the rates of measured losses (ET) are consistently
higher than PE calculated for the same conditions (see free-water evap-
oration, Figure 7-18) and are generally much greater.
All of the lysimeter tests plotted in Figure 7-18 were made dur-
ing the warm season of the year. A reasonable assumption is that at
the lower end of the scale, reflecting the dormant season, ET should
approximate open-water evaporation, or PE. Therefore, a curve was
drawn defining the relationship between the water hyacinth loss rate
and the PE rate through the centroid of plotted points of Figure 7-18
and asyratotic to open-water evaporation rate at the lower end. This
curve was used to estimate monthly values of evapotranspiration from
water hyacinth cover and thereby complete the water-balance calcula-
tion. The bar diagram of Figure 7-19 illustrates this calculation
for the station at Jeanerette, Louisiana. This diagram is based on
26-year averages and indicates the probable presence of long-term
water deficits in areas covered by water hyacinths as opposed to net
water-yield from other types of surface cover.
As discussed in the previous paragraph, three types of surface
cover were distinguished in the determination of net gain or loss of
water from a given area. These are dry-land surface, non-hyacinth-
covered wetland, and water hyacinth-covered wetland. The relative
proportion of each type of cover is therefore an important factor in
the determination of net water-yield from a management unit. The
amount of dry-land area is a function of water level and topography
and can be obtained by the procedure described earlier. The extent
of water hyacinth was estimated from examination of recent aerial
photographs of the floodway taken by NASA, supplemented by gross
estimates furnished by the Louisiana Wild Life and Fisheries Commis-
sion. The results are summarized in Table 7-5.
The formula applied in the computation of water yield on a unit-
wide basis is as follows:
Y = 0.83148(1 - WS) + (1-WH)(P - PE) + WH(P-ET)WS,
where Y is water yield in inches, S is land runoff in inches, P - PE
is gain or loss of water from the non-hyacinth water surface in inches
P " ET is gain or loss of water from the hyacinth-covered water surface
in inches, WS is the ratio of water surface to total area of the unit
and WH is the ratio of water hyacinth-covered area to water-surface '
area. The coefficient of the first term on the right-hand side of the
157Timmer and Weldon, 1967, op_. cit.
121
-------
millimeters/day
2 3
Lysimeter data (Penfound and Earle, 1946;
Timmer and Weldon, 1967)
15
(0
^
CO
10 ••-
0)
E
E
.04 .08
Computed Potential Evapo-transpiration, inches/day
.24
—' 0
Figure 7-18. Evapotranspiration from a free-water surface and a hyacinth covered surface,
respectively
-------
A. DRY LAND SURFACE
PRECIPITATION
-5
-10 I-
B. OPEN WATER SURFACE
C. WATER HYACINTH SURFACE
15
15
(0
«
*j
0>
15
-15
-30
1 ' ' ' '
' ' ' '
JFMAMJJASOND
months
Figure 7-19. Water balance illustrating difference in water yields
and losses for land surface, open-water surface, and
hyacinth- covered water surface, respectively.
123
-------
Table 7-5. . Pertinent Data, Water Management Units.
West Floodway
Bayou Fordoche
Warner Lake
Cocodrie Swamp
Beau Bayou
Buffalo Cove
Six Mile Lake
Morganza Floodway
Alabama Bayou
Bayou des Glaises
Pigeon Bay
Flat Lake
The Crevasse
Upper Belle River
SYM
Wl
W2
W3
W4
W5
W6
W7
El
E2
E3
E4
E5
E6
E7
AREA (MI2)
211
123
34
60
33
91
48
99
77
100
59
70
55
192
Water Hyacinth
Coverage (%)
.05
.10
.15
.15
.15
.40
.05
.05
.10
.15
.15
.10
.05
.15
124
-------
equation is the land-runoff adjustment factor obtained by correlation
with observed streamflow, as described in an earlier report.158
Volume of water yield in million cubic feet is a more convenient
unit for water-management calculations and is obtained by means of the
following conversion formula:
Y(MCF) = Y(INCHES)A (SQ. MILES) 2.3232,
where A is the total area of the management unit.
An example of a water-yield computation is shown in Table 7-6 for
the Buffalo Cove Unit. Normal monthly values of yield are computed
utilizing water-balance data derived for the Jeanerette, Louisiana,sta-
tion. The area of the unit is 236 km2 (91 mi2), and water hyacinth
coverage was estimated to be 40%. Similar data were developed for the
other units, and the results are summarized in Tables 7-7 and 7-8.
Previous discussion of basin hydrology revealed a major reduc-
tion of water levels and aquatic habitat as a result of Center Channel
construction. Diminution of this effect would require measures to re-
tain water within the management units and/or introduction of supple-
mental water. Likewise, any replacement of required river-water inflow
by precipitation surplus as a measure to reduce siltation would call
for water storage. Storage characteristics of individual management
units for specific water levels are therefore a major concern.
The hypsometric curve of the management unit forms the basis for
determining the capacity of that unit to store water. The integrated
area between a given water-surface elevation and a minimum reference ele-
vation, shown diagrammatically in Figure 7-20, multiplied by a scale
factor, provides the storage content for that particular water level.
A series of these values, computed and plotted from minimum to maximum
elevation, forms the storage-elevation curve for the unit. Utilizing
individual hypsometric curves, storage-elevation curves were determined
for the lower nine floodway management units dominated by swamp habi-
tat. These curves are shown in Figures 7-21 and 7-22 for the units to
the east and west of the Main Channel, respectively. Differences in
steepness between the curves reflect the increase in ground slope
toward the north.
The storage curve allows determination of the volume of water re-
quired to raise the water level in a managed unit to the desired level,
or conversely, of the volume released when the water level falls to a
given stage. It is an indispensable tool in determining water needs to
fulfill management requirements and will be further applied in subse-
quent sections dealing with plan development.
158Coastal Environments, Inc., 1974a, op. cit,
125
-------
Table 7-6. Water-Yield Computation, Buffalo Cove Management Unit.
January
February
March
April
May
June
July
August
Sep tember
October
November
December
TOTAL
S
3.60
3.81
2.52
1.17
0.81
0.63
1.73
0.86
0.27
1.11
0.76
3.63
20.90
P-PE
3.63
3.77
2.34
0.58
-0.55
-0.62
1.70
0.19
-0.90
0.64
2.12
4.51
17.41
P-ET
)3.)36
3.37
1.07
-3.49
-9.31
-13.53
-13.32
-12.91
-9.94
-2.72
1.35
4.18
-51.89
STAGE
6.4
6.8
8.7
10.7
10.3
8.0
5.4
4.2
3.5
4.0
3.7
5.0
WS
.59
.65
.79
.87
.86
.76
.47
.29
.22
.27
.23
.43
YIELD
INCHES
3.30
3.46
1.89
-0.98
-3.39
-4.27
-1.26
-0.96
-0.82
0.48
0.90
3.60
1.95
YIELD
MCF
699
730
399
-208
-717
-903
-267
-202
-173
102
191
762
413
126
-------
Table 7-7, Normal" Monthly Water Yield in Million Cubic Feet, Manage-
ment Units in West Side of Floodway.
Month Wl
January 2026
February 1863
March 1333
April 950
May 742
June 167
July 106
August 0
September 4
October 86
November 408
December 1050
Total 9050
W2
1148
1163
749
246
-63
-577
-198
-380
-283
-31
396
984
3154
Units*
W4
478
502
326
67
-104
-182
60
-16
-29
62
123
423
1710
W5
266
282
180
27
-75
-122
23
1
-3
35
62
236
912
W6
699
730
399
-208
-717
-903
-267
-202
-173
102
191
762
413
*Wi = West Floodway
W2 = Bayou Fordoche
W^ = Cocodrie Swamp
W5 = Beau Bayou
W6 = Buffalo Cove
127
-------
Table 7-8. Normal Monthly Water Yield in Million Cubic Feet,
Management Units in East Side of Floodway.
Month El
January 652
February 680
March 461
April 234
May 149
June -57
July 72
August -40
September -68
October 16
November 210
December 522
TOTAL 2831
El = Morganza Floodway
E2 = Alabama Bayou
E3 = Bayou des Galises
E4 - Pigeon Bay
E5 «= Flat Lake
E6 = The Crevasse
E7 - Upper Belle River
E2
950
874
625
446
348
78
50
0
22
40
191
641
4252
E3
815
868
618
172
-83
-343
58
30
18
50
167
582
2952
Units*
E4
242
471
292
20
-182
-198
115
40
4
125
105
465
1499
E5
577
650
461
133
-142
-437
-150
-231
-6
-66
308
679
1776
E6
570
525
377
224
91
-144
-97
-131
• -74
7
180
439
1967
E7
1589
1708
897
110
-905
-1453
-492
-642
-282
149
749
1798
3226
128
-------
30
25
O 20
Z 15
REFERENCE ELEVATION
0
20 40 60 80
CUMULATIVE FREQUENCY
co
Qi
Figure 7-20. Graph showing use of hypsometric curve in
determining storage capacity of management
unit for given water level. Shaded area is
representative of storage content.
129
-------
100
1000 meters3
200 300
400
50O
16
20
Storage, met
Figure 7-21.
Storage elevation curves for management units in east floodway.
relate stored volume of water to stage.
Curves
-------
16°r
12 -
(O
E
to
10O
1OOO meters3
20O 300
CO
0)
8 12
Storage, mcf
16
20
Figure 7-22.
Storage elevation curves for managements units in west floodway.
relate stored volume of water to stage.
Curves
-------
VIII
THE PRESENT AND FUTURE MAIN CHANNEL
Throughout this study, the assumption has been made that overriding
use for the middle basin is as a floodway, with the Main Channel the
principal element in flood control. To meet flood control requirements,
the channel should maximize sediment movement through the basin so that
reduction of floodway cross-sectional area, and deterioration of
aquatic habitat as well, is kept at a minimum. This requires minimi-
zation of deposition in the overbank area and of channel in-fillings
requiring maintenance dredging and spoil deposition.
Minimization of overbank deposition requires control over diversion
of sediment-laden water into the backwater areas. Minimizing channel
maintenance requires that the proposed Center Channel conform as
closely as possible to a stable, natural channel whose dimensions are
in equilibrium with the Atchafalaya River regime of discharge and
sediment load. From the point of view of energy expenditure, it is
furthermore desirable to capitalize on the useful energy provided by the
river in obtaining channel modification required for flood control.
The above aspects will be considered here in the light of present
channel conditions and trends at locations referenced in Figure 8-1,
and relationships between channel geometry and flow parameters. Results
will then be compared with hydraulic geometry and related aspects of
the proposed Center Channel.
Channel Dimensions
Present and proposed channel dimensions are summarized in graphical
form in Figures 8-2 and 8-3. Figure 8-2 shows the channel cross-
sectional area for bankfull stage at subsequent intervals of 4 km (2.5
miles) below the origin of the Atchafalaya River. Channel areas used
for 1963 and 1970-73 (most recent) are those presented for bankfull
condition in the U.S.C.E. Environmental Statement Appendix.159 Bankfull
area for the proposed Center Channel was calculated from cross sections
provided by the U.S.C.E., New Orleans District. Most recent and 1963
cross-sectional data reveal a relatively stable channel over the first
50 miles,with an average value of 8980 m2 (96,000 ft2}; It should be
pointed out that this value concerns the channel proper. As explained
previously, channel cross section is larger'when taking into account
the artificial levees extending the channel banks upward. In the latter
case, the. channel exceeds 9300 m2 (100,000 ft2). Between mile 50 and
55, cross section rapidly decreases. The most recent survey shows a
Army Corps of Engineers, 1974, op.cit.
132
-------
fltchafalayo Basin. La
Figure 8-1. Reference location along Main Channel of Atcha-
falaya River.
133
-------
o
C3
Cfl
-
c
M
~
X
—
rt
-
n
:
=
H
-
—
w
=
-
'
r
• -
o a* o
H- to i-i
330
01
Ml CO
§
I CO C
O> N3 O M (D
O-^ 3 O
- CO M rt
(K H-
cu to < o
3 i-l (D 3
ex. ID i—1 to
M
•o co to
^ 3* w to
o o ^
T3 fi CL (D
O 3 fD M
CO h-h
(D i-h H- O
CL O 3 Mi
n
tt>
3
rf
fD
o cr
n g -o BJ
3* O O 3
B) CO (TO 3
3 rt
3
M
T)
(D
n
O fD
O 3
3 rt
CL
"
'.
Miles Below Head
-------
kilometers
100
--
- 20
100
Miles Below Head
Figure 8-3. Width and mean depth of Main Channel at bankfull stage for 1963, most recent (1969-1972),
and proposed Center Channel conditions.
-------
cross section of approximately 5100 m2(55,000 ft2) between mile 50 and
80 and a further decrease to 4650 m2 (50,000 ft^) at mile 95, and 1850 m2
(20,000 ft2) at mile 110.
A number of factors contribute to the various decreases in cross
sections downstream from mile 50. One is youth of the channel. Geolo-
gically speaking, conversion from a series of lakes to a generally
confined channel has only occurred recently or is still ongoing, such
as in Six Mile Lake, from mile 100 to 110. A second major factor
relates to loss of channel discharge in the downstream directions.
Whereas even the highest discharges are contained by the channel above
mile 55 because of continuous artificial levees, below mile 55,increas-
ing volumes of water are diverted from the Main Channel as discharge
increases. For a flow slightly above bankfull discharge, 30 percent
of the flow is diverted at mile 50 from the Main Channel into the old
Atchafalaya River channel,with only 11 percent returning at the down-
stream confluence. Further loss amounting to about 15 percent occurs
at the East Freshwater Diversion and Access Channels and through lesser
openings in the banks. In other words, between mile 55 and mile 95,
the Main Channel is only carrying from 60 to 70 percent of the original
discharge since most water is diverted into the overbank area to the
west. A temporary increase in discharge occurs between mile 95 and 100
as water from the western swamps is routed back into the channel.
However, 30 percent of the original discharge is again diverted from
the Main Channel at mile 100 toward Wax Lake Outlet. Thus, for most
of the distance between mile 100 and 110, only about 50 percent of the
original discharge is contained by the Main Channel. Prior to entering
the Lower Atchafalaya River, flow is increased again to 70 percent
through drainage from the eastern swamp basin. Comparision of the
above information with Figure 8-2 immediately shows that successive
decreases in cross-sectional area reflect the identified decreases in
discharge.
Since 1963, cross-sectional area has increased by approximately
30 percent in the lower channel below mile 55, as illustrated by the
diagram (Figure 8-2). The increase resulted partially from dredging
and spoil deposition that limited overbank escape of channel flow. Since
the proportional contribution of natural and human processes is not
fully known to the authors, no accurate estimate can be made here of
the natural rate of increase. Natural enlargement to the proposed
dimension shown in Figure 8-2 has been estimated at-'a period of 40
years under present conditions of flow distribution;!61 through dredg-
ing, enlargement is estimated to take a period of 15 years.
The proposed channel cross section is seen to represent basically
a continuation of the cross-sectional trend established along the river
I61lbid.
136
-------
above mile 55. Since no changes are planned to eliminate major routes
of flow diversion from the lower channel, the question arises as to
what extent the proposed cross section will be in adjustment to the
normal Atchafalaya River regime and whether the proposed channel will
be self-maintaining. The following discussion will address these
questions.
Hydraulic Geometry
No channel will be stable throughout the range of discharges
experienced by the Atchafalaya River. Scour and infilling will alter-
nate with annual changes in discharge. However, it is generally accepted
that the geometry of mature stream channels is governed by flow charac-
teristics for bankfull discharge, which is defined as that discharge
having a recurrence interval of 1.58 years.162,163 Analysis of
Atchafalaya River flows revealed that bankfull discharge as based on
frequency of occurrence can be set at 11,300 cms (400,000 cfs). For
this discharge, hydraulic geometry and associated parametric values
can be obtained for the Main Channel in its stable upper reaches
Through processing of weekly data obtained by the U. S. Corps of Engi-
neers at Simmesport (mile 4.8),164 ratlng curves and equations wer°
developed relating discharge (Q) to stream width (W), mean depths (D)
cross-sectional area (A), mean velocity (V), and stage (H). Figures '
8-4 and 8-5 show the curves; the following relationships were obtained:
F s
D = 1.571Q0'2297 D = 2.273Q0-2297 (1)
W = 117.6Q°'1433 w = 2.31.5Q0-1143 (2)
A = 184.8Q0'3730 A = 526.3Q°'3730 (3)
V = 0.0054Q0'6270 v = 0.0019Q0'6270
!62L. B. Leopold, et. al., Fluvial Processes in Geomorphnlnpy
(San Franciso: W. H. Freeman and Company, 1964) 522p.
163 G. Dury, " Magnitude Frequency Analysis and Channel Morphology"
(State University of New York, Binghamton, New York, in M. Morisawa
ed., Fluvial Geomorphology. Publications ^n Geomorphology,.1973), Part 2.
164 U.S. Army Corps of Engineers, Stages and Discharges of the
Mississippi River and Tributaries and Other Watersheds in the New Orleans
District for 1965 (New Orleans District, New Orleans, Louisiana 1965) 403 P
137
-------
cms
*- 50
0) 40
•^
JC 30
"5.
0)
5OO 100O
1—I 1 I I I I
sooo 10.000
T 1 1 1—I I I I I
0=2.273 Q
0.230
0) 20
H-
O
15
10
10
U
O
1
10
':213.5 Q0143
V:0.0019 Q0627
J L
50 100
(Q) Discharge, 1000 cfs
500
15
10
600
500
400
300 w
£
E
2.5
2.0
1.5
1.0
0.5
1000
Figure 8-^
Relationships between mean depth, width, mean velocity,
and discharge of Atchafalaya River at Simmesport, Mile 4.8..165
165
Ibid.
138
-------
10OO
100
50
(0
fi o
oT
O)
(0
4-1
(0
cms
5000
T T
^___ 10000
T 1 1 I 1 I I
50
i i i
100
i—» » » »
20
10
CO
(5
+*
0)
1000
Discharge, 1000 cfs
Figure 8-5. Stage-discharge relationship for Atchafalaya River
Simmesport, mile A.S.
at
166
Ibid.
139
-------
Table 8-1 summarizes flow conditions for 11,300 cms (400,000 cfs)
discharge also including the gradient (S) and Manning's roughness
factor (n).
Table 8-1. Flow Parameters, Atchafalaya River, Mile 4.8.
Q.
cms cfs
11,300 400,000
D
m ft
13 44
W
m ft
448 147
A
m2 ft2
0009 64685
V
m/s ft/s
1.9 6.2
H(MSL)
m ft
11.9 39
S
.000059
jn
.023
With the obtained relationships, theoretical channel Dimensions
can be determined if a trapezoidal, cross-sectional shape and a bank
slope of 0.3 in accordance with the na^al channel are a ssume d The
channel cross section as obtained for 11,300 cms (400,000 cfs) is
shown in Figure 8-6 together with the actual cross section.
Comoarison of the two cross sections shows fair agreement in
and width, but depth is conside ^ S-ater^n the
TV.-JQ difference appears most important, me actual
promeurve™ d»"ng low discharge and stage. «hen calculating
pronie was surveyc e ,ncrliflree it is found that bottom eleva-
SSrsrsSsssn.-jr-T.waa--
or 4 m (13 ft) lower than the bottom eleva-
.
suspended sediment concentration with increasing discharge.
Prior to examining the consequences of the above- analysis one
additional observation should be made. The presence of artificial
167Leopold et. al., 1964, op_. cit.
168L B Leopold and T. Maddock, Jr., The Hydraulic Geometry of
n, frhimnels and Some Physiographic Implications (Professional Paper
u. S. Geological Survey, Washington, D. C., 1953), 56 p.
140
-------
feet
60
4O
_ 20
CO
2000
-2O
-40
1600
I. AVERAGE 1963-1967
7204
W=482 m
D=15m
V=1.6m/s
12OO
800
—I—
400
ATCHAFALAYA RIVER, SIMMESPORT (mil* 4.8)
11.327 cms (4OO.OOO cfs)
O
CALCULATED NATURAL
A=6OO9m2
W» 447m
D= 13.5 m
V=1.9m/«
15
10
5 £
9
-5
-10
600
400
200
meters
Figure 8-6. Cross sections of Atchafalaya River at Simmesport, mile 4.8, obtained from U.S.C.E.
survey and through calculations, respectively. ^
169
U. S. Army Corps of Engineers, 1974 ^ op. cit,
-------
2000
ro
40
75 20
E
0>
0>
-2O
-40
6OO
1600
feet
1200 800
400
ATCHAFALAYA RIVER (mile 4.8)
PRESENT (low discharge)
400
200
-0=500,000 cfs
- 400,000
- 300,000
- 200,000
100,000
15
10
5
0)
**
0>
-5
-10
meters
Figure 8-7. Cross sections of Atchafalaya River at Simmesport, mile 4.8, as obtained from
calculations for various discharges.
-------
levees along the upper reaches of the Main Channel confines flow also
for discharges above 11,300 cms (400,000 cfs). As a result, stages
for a given discharge exceeding the latter value are higher than they
would be under natural circumstances, where the river would overflow
into the floodplain; channel banks are therefore allowed to build up
to a higher level. The artificial levees have the effect of increas-
ing the magnitude of flow at which bankfull discharge is reached. In
the cross section analyzed in Figure 8-6, bankfull discharge as
defined by topography is attained at a stage of 14.3 m (46.8 ft) MSL,170
which is associated with a discharge of about 14,150 cms (500,000 cfs)
rather than the 11,300 cms (400,000 cfs) expected if natural condi-
tions prevailed. Channel cross-sectional area for this larger dis-
charge as obtained from Equation (3) is 6,500 m2 (70,300 ft2).
The above value is considerably smaller than those indicated in
Figure 8-2. Only by taking the total area containing all probable
channels for discharges below 14,000 cms (500,000 cfs) is a cross-
sectional value of about 8400 m2 (90,000 ft2) obtained. Consequently,
to place cross-sectional data in a proper perspective, it should be
stated that 1) self-maintaining channel capacity for bankfull discharge
is about 6000 m^ (65,000 ft2), and 2) in the presence of artificial
levees, the area utilized by the Atchafalaya River for discharges up
to 14,000 cms (500,000 cfs) is in the order of 8400 m2 (90,000 ft2).
Probable Natural Channel
One may now view the overall Atchafalaya River system in order to
obtain a notion of the dynamic equilibrium conditions the river is
attempting to realize. For this purpose, a single channel is assumed
connecting the Mississippi River and Atchafalaya Bay, having a bankfull
discharge of 11,300 cms (400,000 cfs) and a length of 225 km (140 miles).
Furthermore, it is assumed that conditions at the head of the river are
stable at present. Thus, limiting conditions for the following discus-
sion are length (L) = 225 km (140 miles) for a discharge of 11,400 cms
(400,000 cfs), stage at mile 4.8 (H4.8) - 11.9 m (39 ft), stage at
mile 140 (H!40) - Om (Oft) and slope at mile 4.8 (84.3) - 0.000059 km/km.
First, the probable flowline can be determined. Applying the
concept that in an open system the distribution of energy tends
toward the statistically most probable, it follows that the most
17°U. S. Army Corps of Engineers, 1974, op.cit.
143
-------
probable stream profile for a poised river is exponential in
form.171,172,173 The most probable river profile can thus be defined
as
X = ae~bh 4- c (5)
or
H - - In ( - £— ) , (6)
b x - c
where X is the distance along the stream as measured from the head of
the river (Xg) , H is the elevation above base level at a point along
the stream, and a, b and c are constants. From equation 5, river
slope (S) can be obtained as
For the limiting conditions stated earlier {H 4.8 = H«9 m (39 ft);
H140 = 0 m (ft); S4>8 = -.059m/km (-0.31152 ft/mi)} (6) and (7) can
be solved for a, b,'and c, so that the river profile becomes
Hx= 256.65 In <--> UO (8)
and slope
=dH= -256.64 ( L_) (ft/mi). (9)
x dx x +819
In Figure 8-8, the obtained stream profile is shown together with
present and proposed profiles for 11,300 cms (400,000 cfs) as obtained
171L. B. Leopold and W. B. Langbein, The Concept of Entropy in Landscape
Evolution (Washington D. C.: Professional Paper 500-A, U. S.
Geological Survey, 1962), 20 p.
172J. T. Hack, "Drainage Adjustments in the Appalachians" in
Fluvial Geomorphology, ed. M. Morisawa (Binghamton, New York: Publica-
tions in Geomorphology,1973).Part 1.
173J. T. Hack., Studies of Longitudinal Stream Profiles in Virginia
and Maryland (Washington, D. C.: Professional Paper 294-B, U. S.
Geological Survey, 1957).
144
-------
kilometers
40
g so
o
I-
UJ
100
200
ATCHAFALAYA BASIN MAIN CHANNEL
0
Figure 8-8.
50
100
12
CO
150
Miles From Head
Water-surface profiles along Main Channel as obtained from U.S.C.E. fixed bed model
study for present (1969) and proposed Center Channel (manmade ultimate) conditions,
and for most probable equilibrium condition (theoretical). Assumed discharge is
11,300 cms (400,000 cfs).174
U.S. Army Corps of Engineers, 1974, op. cit.
-------
from the U.S.C.E. model report.17-* Comparison of the profiles shows
coincidence of present and probable equilibrium conditions in the upper
half of the stream, supporting the assumption of a stable channel in
that reach. Center Channel conditions can be observed to move the
river in a direction away from dynamic equilibrium by further decreas-
ing an already low gradient in the lower reaches. On the basis of
deviation between present and theoretical profile, a trend toward
increased gradient and stage must be expected for the lower channel.
This can be partly substantiated by Figure 8-9, which shows such a
trend at both Morgan City and Wax Lake Outlet over the past 20 years.
At Morgan City, the average increase has been 0.017 m (0.055 ft)
annually. Projection of this rate suggests that natural channel devel-
opment would take approximately 45 years.
To further evaluate proposed and present conditions, one can
compare channel cross sections with their respective probable future
cross sections. Figure 8-10 shows the cross section at mile 75,
approximately halfway down the proposed Center Channel. Water levels
shown are those associated with an 11,300 cms (400,000 cfs) discharge,
as obtained from the U.S.C.E. model study176 and equation (8).
Cross section for the probable equilibrium condition, was calculated
using the procedure outlined for mile 4.8, but taking into consider-
ation the lesser gradient as obtained from equation (9). Mean velo-
city was assumed constant over the entire channel length in accordance
with natural streams.177 In the absence of tributaries, discharge
must also be assumed to be constant and,consequently, cross-sectional
area. Roughness was assumed constant on the basis of constant
velocity and sediment load.
Comparison of the profiles suggests 1) that the channel trend
should be toward a larger width, and 2) that width of the proposed
channel is excessive and is not in equilibrium with the Atchafalaya
River discharge and load regime. The first suggestion is supported
circumstantially by the fact that an increase in width from 256 m
(840 ft) to 357 m (1170 ft) over the period 1963-1969 has been main-
tained.
The second conclusion can be supported by the following consid-
eration. The cross-sectional area occupied by flow in the proposed
channel measures 7150 m2 (77,000 ft2). For a discharge of 11,300 cms
(400,000 cfs), a velocity of 1.58 m/sec (5.2 ft/s) would be required.
Design gradient, however, is only 0.000024, while hydraulic radius
measures 13.9 m (45.5 ft). For an assumed roughness of 0.023, the
U. S. Army Corps of Engineers, 1974, op. cit.
176Ibid.
Leopold et al,., 1964, op. cit.
146
-------
NOVEMBER
LOWER ATCHAFALAYA
RIVER,
MORGAN CITY
WAX LAKE OUTLET
LOWER ATCHAFALAYA
RIVER,
MORGAN CITY
-Ifl
WAX LAKE OUTLET
1*03 IMS
Years
1070
itn
Figure 8-9.
Trends of river stage for Lower Atchafalaya River
at Morgan City and Wax Lake Outlet at Calumet re-
veal gradual increase of mean monthly stage for
high and low discharge months, respectively.
147
-------
feet
2000
20
1600
12OO
800
400
oo
— o
E
O
3-20
-40t-
ATCHAFALAYA RIVER, (mil* 75.1)
11,327 cms (400,000 cfs)
II. PROBABLE EQUILIBRIUM
IIIIIIIIIIIIIIIIIMIIIMIIIIIIIIIIIilllll
Tlllltllllllllllllllllllllllllllllllllllllllllllllll?
10
0
to
o
o
-s£
-10
III. PROPOSED
600
400
200
meters
Figure $ -10.
Cross sections of Atchafalaya River Main Channel at mile 75.1 as surveyed in 1969, as
proposed, and as obtained for most probable equilibrium conditions at bankfull discharge.
-------
Manning equation yields a velocity of 1.2 m/sec (4.0 ft/s). Under
this condition, the stream can be expected to respond by reducing
its width, maintaining cross-sectional area through a corresponding
rise in water level which, in turn, produces an increased hydraulic
radius and slope and,consequently, an increase in velocity. Width
reduction can only be obtained through sediment deposition. Both
the reduction in width and the rise in water level are seen to move
in the direction of equilibrium channel conditions.
Two additional points should be made. First, it should be noted
that the required 1.58 m/sec (5.2 ft/sec) represents a considerable
decrease in velocity from the 1.9 m/sec (6.1 ft/sec) associated with
the same discharge in the upper channel section. Consequently,
carrying capacity of sediment load must be expected to decrease and
to result in additional sedimentation. Secondly, flow diversion,
which ranges from 20 to 30 percent of the discharge, has been ignored.
This, in effect, decreases the channel controlling discharge and,
consequently, the self-maintaining channel cross section.
In summary, analysis of hydraulic geometry under the present
Atchafalaya River regime of discharge and sediment load suggests that
the proposed Center Channel dimensions, particularly width, exceed
those required by the channel controlling discharge of 11,300 cms
(400,000 cfs). On the basis of the previous analysis, it is believed
that an efficient, self-maintaining channel cannot be realized if
cross-sectional area below the projected floodflow line exceeds
7,500 mz (80,000 ft2) and a width of about 425 m (1400 ft). Exceeding
this magnitude by 1250 mz (20,000 ft2), or 25 percent, in order to
obtain a dynamic equilibrium and optimum flow efficiency for project
flood discharge conditions appears to ignore the fact that the Center
Channel will adjust to its resident stream rather than to a low
frequency occurence, such as major floods requiring maximum diversion
of Mississippi River discharges.
149
-------
IX
PLAN FOR MANAGEMENT OF THE ATCHAFALAYA BASIN
In this chapter, we shall first define zones and strategies for
land and water management which will best accommodate, in our view,
the many management possibilities that are presently or potentially
important in the Atchafalaya Basin. Secondly, a detailed surface
water management plan will be set forth.
Definition of Management Zones
The management zones are meant to incorporate as many possible
existing land uses that are compatible with the major management
objectives. In the Atchafalaya Floodway, for instance, the primary
management objective must be flood control since this is of key impor-
tance to a large segment of Louisiana. However, the acceptance of this
as a primary use does not preclude needs to mitigate as much as pos-
sible the effects of flood control on other uses. Certainly this
should be done in cases where the mitigation actually might enhance
flood-control use. As we shall show in the following, there are
many opportunities for compatible multiple use of this kind.
Management zones are grouped into three categories,which we term
zones of protective use, exploitative use, and a buffer zone (Figure
11-1). The zone of protective use includes mostly the present areas
of swamp forest and other bottomland forests that have been least
utilized by humans other than for flood-control purposes. The zone
of exploitative use includes those areas where substantial human
development has already occurred mostly from agricultural, urban,
industrial, and residential uses. The buffer zone is proposed herein
as a tract lying between the two in which planning should focus on
ways to minimize the many conflicts between exploitative and protec-
tive use.
It should be realized, however, that in actual fact these divi-
sions are somewhat arbitrary. All of these zones are presently under
exploitative use by humans. The Atchafalaya Floodway is certainly in
exploitative use since it is a floodway. By including it in the zone
of protective use as we do, we mean to emphasize that our principal
concern should be protection not only of wildlife and vegetational
habitat value, but also of its value for human use as a floodway.
On the other hand, lands in exploitative use,such as the agri-
cultural lands,also deserve much consideration in order to protect
their quality as agricultural lands. So protective-use considerations
are extremely important in this case as well. Also, places within
the zone of exploitative use that still retain some more or less
natural attributes might also be consigned to protective use
150
-------
fltchofaloyo Basin. La.
PROPOSED LAND-USE MANAGEMENT
Figure 9-1. Proposed zonation of protective and exploitative
land uses separated by a buffer zone and allowing
multi-use management of the Atchafalaya Basin.
151
-------
management . This would apply to scattered locations where bottom-
land hardwoods have not been entirely removed.
In the buffer zone especially there will be much mixture of pro-
tective and exploitative use. An exploitative use for which this zone
might serve would be as a biological tertiary treatment area for
municipal wastewater, designed so that it might yield a useful product
such as pulpwood, methane gas, methanol, or other chemicals. This
use could be considered protective, however, since it could free an
even larger area from the impact of pollution. Various schemes of
biological water treatment may be used in this buffer zone to pro-
cess agricultural runoff for recovery of soil and nutrients lost
from fields.
We do not propose that the zones outlined on Figure 9-1 be
viewed as final or fixed. Rather, the plan should be viewed as flex-
ible, with modification and shifting of zones as it becomes appropriate
to do so. Should future trends be toward reduced need of lands in
crops or pasture,then the lowest-lying agricultural lands on the flanks
of the natural levee ridges could be transferred into the buffer-zone
management area,with corresponding transfers from that zone into the
zone of protective use. In areas where agricultural lands are presently
flood prone, such transfers also might be appropriate in lieu of
expanded drainage efforts.
Although the zones as outlined have a banded structure, with
exploitative use occurring on the higher ridge lands, buffer-zone use
at intermediate levels, and protective-use areas occupying the swamp
basins, this should not necessarily be regarded as an ideal or final
pattern. It would be highly desirable in the future if needs for land
in exploitative use should decline to have zones of protective use
extend completely across levee ridges, providing corridors to connect
protective-use zones on opposite sides of the levee ridge. These
corridors would reduce the present fragmentation and isolation of
habitat and increase its diversity.
Strategies for Management
First consideration must be given to flood control of the Atcha-
falaya Basin since this is of key importance to a large segment of
Louisiana and since there ate no adequate alternatives to the use of
the basin for floodwater routing and storage. Secondary considerations
are to bring about as much compatibility as possible of natural
resource and cultural use values with the necessary flood-control
measures.
152
-------
Protective Use Zone
Fluvial Swamps
The use of the Atchafalaya Basin with its existing flood control
works seems mandatory to any program of flood mitigation in Louisiana's
alluvial and coastal lowlands simply because it is the largest avail-
able basin in which such a purpose can be accomplished. Additional
floodway outlets,such as the Bonnet Carre Spillway and others,which
may be required in the future are not likely to significantly reduce
the need for this large basin for some time to come.
Relocation of the principal floodway outlet would require large
amounts of land now in other use and will create numerous environmental
changes of the kind described as occurring in the Atchafalaya Basin.
Therefore, it is absolutely imperative that we direct critical atten-
tion to means of prolonging for as long as possible the useful life
of the basin for flood-control purposes.
A flood-control feature such as the Atchafalaya Floodway serves
two useful purposes. It provides storage of floodwaters, and it
carries the floodwaters away from areas which might otherwise be
endangered. The most effective use, then, of such a floodway should
emphasize the following points:
1) The storage capacity or total amount of water which the flood-
way can hold should be conserved by every means at our disposal. Each
time the floodway is used for routing of a major flood,some storage
capacity will inevitably be lost through sedimentation. Such losses
should be minimized at all other times since the dwindling of storage
capacity subtracts irreversibly from the useful life of the floodway.
When it is considered that the replacement of this feature would cost
an enormous amount, then the value of strict conservation of storage
capacity is readily apparent.
2) The ability of the principal channel or channels to carry
a large volume of the excess floodwaters should be as great as can be
maintained. This increases the amount of water that is carried within
the channel and allows for passage of greater total floodwater volume.
Just as importantly, however, it also means that a greater proportion of
sediment-bearing floodwater will pass through the system without leav-
ing the channel, and therefore will not contribute to sedimentation
and loss of storage capacity.
If we are to significantly prolong the useful life of the Atcha-
falaya Floodway, both of these related points will require critical
attention. Although the emphasis given here is to the value of the
lands for flood-control purposes, it is readily apparent that the way
153
-------
in which water and sediment are routed through the basin has numerous
ramifications related to other uses.
Within the floodway, the management strategy is aimed primarily
toward careful and controlled regulation of water inputs. Three of
the primary goals of this strategy are to reduce sedimentation, to
allow sufficient dewatering, and to protect water quality. Regulated
backwater stage-variation will be timed 1) to benefit established
tree communities that are intolerant to flooding or sedimentation, 2)
to achieve improved tree growth, 3) to benefit crawfishing activity
and crawfish reproduction, 4) to benefit fishing activity and fish
propagation,5) to control aquatic weeds, and 6) to improve water
quality. Table 7-3 indicated how these objectives are related to
lands of five hydroperiod intervals.
It is expected that individual landowners will make the most
appropriate uses of lands of varying hydroperiod classes under the
managed regimes. Some forms of silviculture may become viable,parti-
cularly for tupelo gum, cypress, and green ash, although much of the
area may be left to natural forest growth with periodic harvesting.
There are, of course, no controls to prevent agricultural develop-
ment except for the periodic large floods which will probably limit
such efforts. Traditional uses,such as fishing, crawfish harvest,
trapping, and hunting,should benefit from the proposed management.
Wherever possible, wildlife management areas should be established.
Land uses related to flood control presently are centered in the
area around the floodway itself, but it is evident that these uses
will inevitably come about in the area of delta growth below the
Teche Ridge. Places such as Gibson and Amelia,which lie east of
Morgan City, already are in need of flood protection from the waters
discharged in the delta area.
Pluvial Swamps
The low-lying lands of the Atchaf alaya Basin which lie outside of
the floodway are referred to here as pluvial swamps since they are
largely dependent on local rainfall and runoff derived from drainage
systems of adjacent developed lands. One of the greatest conflicts
in land and water management in the Atchafalaya Basin is that which
exists between such developed areas and those which to some degree
retain their natural attributes. In developed areasi' which may be
of agricultural, urban, suburban, or industrial type, the predom-
inant strategy for water management at present is to^remove the water
as rapidly as it comes in through rainfall since it is an impediment
to many activities related to these kinds of land uses. In order to
remove this water rapidly, canals have been dug, streams have been
channelized, the terrain has been extensively ditched, and storm
154
-------
sewer systems have been installed. Additional water not derived from
local rainfall may also be discharged through municipal, industrial
and even residential water supply systems which draw water from the
ground or take water from rivers. All such waters discharged from
the developed areas may carry with them varying amounts of agricul-
tural, municipal, and industrial pollution.
The undeveloped areas are, for the most part, the lower-lying
swamp basins where water removal is too difficult or costly for them
to be used in the ways described above. These are used as receiving
basins for waters discharged from the developed areas. Thus, these
basins are made use of as natural storage areas and treatment systems
for such waters. Although it is sometimes said that these uses consti-
tute a free' work of nature, it is incorrect to think of this as a
use without cost since there are usually destructive consequences of
use which may be overlooked. For instance, the water which is discharg-
ed into the Verret-Palourde Basin from a large area of developed
natural levee land along the Mississippi River - Bayou Lafourche -
Bayou Black levee ridge contributes to destructive flooding in commun-
ities such as Pierre Part, Stephenville, and Gibson. The result of
such situations is usually a public demand for more-of-the-same drain-
age improvements or other systems of flood protection.
The pluvial swamps should be managed for protective use for
several reasons. They constitute high quality habitat for wildlife
and fish. They have intrinsically high recreational and scenic value.
The use of these swamps for runoff routing and storage is essential
to present developed areas. One of the most important needs for
these lands is due to the fact that, barring completely unanticipated
changes in the Mississippi River system, it must be concluded that at
some time in the future,the useful life of the present floodway will
be ended. For this reason, it is necessary to view the low-lying
areas of the basin which lie outside of the present floodway as poten-
tial alternate areas for flood diversion. Much of the management
strategy that is appropriate for protection of the pluvial swamps
does not require action in this zone itself, but requires careful re-
thinking of the mode of use of the developed lands. Particularly, the
amount of runoff water discharged into the pluvial swamp area should
be reduced, as should the quantities of associated pollutants. If
this is not done, there will no doubt be increased pressure for drain-
age canals and additional floodwater outlets as well as continued
deterioration of water quality in this zone. Means for increasing
the storage capacity of water on the lands from which the runoff is
derived should be actively investigated. Alternative agricultural
techniques which have lesser needs for drainage should be given inten-
sive attention. Human settlements and their accessory developments
such as roads, should be developed by adaptive strategies which lessen
drainage needs. Some possibilities of these kinds are discussed in
the following sections of this chapter dealing with those lands.
155
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Buffer Zone
It is proposed that a buffer zone be placed between zones managed
for protective use and those managed for exploitative use. This zone
may be managed in various places either for exploitative or protective
uses, but the emphasis should be given to a reduction of certain incom-
patabilities between the zones to either side. For instance, such a
buffer zone situated next to an agricultural area could be used as a
biological treatment system for agricultural runoff waters so that when
such waters are later discharged into the zone of protective use, they
will not contribute pollutants or excessive nutrient loads. Likewise,
runoff waters from industrial, municipal, or residential land use
areas could be applied after appropriate pre-treatment where necessary.
There are many methods whereby this could be accomplished. The
field-drainage systems of the agricultural area could be integrated to
deliver waters for various applications in the buffer zone in which
productive use might be made of residual nutrients. As a particular
example, an area might be managed for short-rotation culture of syca-
more for pulp,with use of the agricultural runoff waters for irrigation
and fertilization. Periodic harvesting of the trees will allow removal
of certain amounts of the accumulated materials that are taken up in
the standing crop.
Similar applications by overland flow of polluted waters may be
used in more conventional forms of silviculture>such as the cultiva-
tion of cottonwood or other species. The water could also simply be
spread by overland flow through unmanaged forest stands to achieve
improved water quality. Much of the water used in such ways will be
lost by evapotranspiration. That which remains, however, could be
used for other purposes.
Aquaculture might be an appropriate undertaking in the buffer
zone, using waters from that zone and runoff waters which have been
appropriately purified by means such as the above. In Louisiana,
notable success has been achieved in aquaculture of blue catfish and
crawfish. The latter can be.cultured with trees standing within the
culture enclosure, and suitable hydroperiod regulation might be of
benefit to both. Another reason for encouraging aquaculture is that
it may be possible through this means to increase the storage capa-
city for runoff water on the buffer zone lands. This could lessen
the flooding problems on lower-lying lands to some e'xtent.
Other techniques that may be appropriate for us^in this buffer
zone are schemes such as that proposed by Wolverton to use water
178
Webre, 1975, op_. cit.
156
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hyacinth for wastewater regeneration. In a treatment system of this
kind, certain fertilizer elements escaping from agricultural lands
may be partially recovered and re-applied to the fields near the
treatment area. Methane gas and fertilizer can be recovered as by-
products through fermentation of the hyacinth under anaerobic condi-
tions, and possibly other by-products could be developed. This
kind of system could potentially be a significant contribution to
local energy needs and, more importantly, may improve the efficiency
of energy use in agriculture.
It is not expected that uses for water regeneration or aquacul-
ture would occupy much of the buffer zone land. A larger part of this
zone might be managed for silviculture of single species or mixed
stands of various trees under varying schemes of management and water-
level regulation. Since the zone lies proximal to the developed
lands, it will be easily accessible for harvest and maintenance oper-
ations. The largest part of the zone might be left to natural devel-
opment or protective use. It would be desirable for a certain area
of this zone to be set aside for experimental use in order to test
varying strategies for management appropriate in this zone.
Exploitative Use Zone
The management of agricultural lands is an area of great uncer-
tainty since future trends are largely dependent on future national, and
even international, policy decisions. Projections can be found for
a decline in land needed for farming nationally179 as well as for an
increase in agriculture in the Lower Mississippi River region. 18°
Future trends will be also dependent on technological innovation.
Especially important are those innovations that may offer hope of
agricultural land use techniques that are not environmentally degrad-
ing and are more efficient, lowering the demand for land.
It seems likely that efficiency of agricultural land use can be
further increased by more intensive cultivation and diversification
of crops. Most cropland presently in the area is in sugar cane, which
has been favored until recently by import quotas which make this prac-
tice competitive with higher-yielding,tropical sugar-producing areas.
%. 0. Heady, et. al., Agricultural and Water Policies and the
Environment (Iowa State University; Center for Agricultural and
Rural Development, 1972),Report 40-T.
180
National Academy of Sciences, Productive Agriculture and a
Quality Environment (Washington, D. C.; National Academy of Sciences
1974) 189p.
157
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By-product recovery from sugar refining has been mainly molasses
and bagasse conversion to paper or fiberboard. Small amounts of sugar-
cane wax are also recovered in Louisiana as well as thermoplastic and
thermosetting resins. Activated carbon, furfural, and alpha-cellulose
are potentially recoverable as by-products. Other opportunities exist,
such as the utilization of both molasses and bagasse in the production
of animal feeds by using these individually or in combination as sub-
strates for production of single cell protein through culture of
yeasts, bacteria, or fungi. Such protein may also be used eventually
for human consumption. With such schemes, feed lots might become an
appropriate agricultural land use associated with sugar refineries.
Manures from the feed lots could then be used for production of methane
gas and fertilizer, with optimum results perhaps obtained by blending
with cellulosic material,such as water hyacinth grown in a water puri-
ification system as proposed by Wolverton.181 In this way, waste from
refining as well as cultivation could be much reduced, and intensifica-
tion and diversification of agricultural land use can be simultaneously
accomplished.
Aquaculture should be more seriously considered as a productive
use of lands in agriculture, particularly those low-lying areas of the
natural levee flanks where drainage is more difficult. Not only should
accepted practices such as culture of catfish or crawfish be employed,
but more innovative culture,such as algae production,should be con-
sidered at least experimentally. Besides its productive potential,
aquaculture offers the potential of increasing the storage of rainfall
and runoff on the agricultural lands.
Other means of increasing the storage of rainfall and runoff on
agricultural lands should be actively investigated. Drainage canals
might be made deeper than needed to convey ordinary runoff and have
outlet controls so that a larger fraction of such waters could be
held in static storage rather than dumped into adjacent basins. Such
waters might be used in irrigation during dry periods.
Future growth of human settlement should be in such a way that
less land will be required with less extensive proliferation of such
accessory developments as roads, water lines, sewer lines, power lines,
and so forth. In urban areas, such densification is already evident
in increased numbers of apartment facilities. Single-family dwellings
also might be arranged in cluster-form in ways that .minimize land
requirements and needless duplication of services.
Industrial land use should undergo similar densification through
better layout and design of facilities and clustering. Certain features
such as air or water pollution abatement facilities might be jointly
181
Webre, 1975, op_. cit.
158
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operated and shared by a cluster of industrial users,with potential
saving of space or improved efficiency of other resource uses.
Surface Water Management
Having defined the distribution of proposed land uses on the
basis of constraints and opportunities set by both the natural
environment and present uses, we may now proceed with definition of
a proposed water management plan. The plan is based on integral
consideration of use and water management requirements of the socio-
economic complex and the forest, fish, and wildlife resources as
discussed in previous chapters.
Flood Control and Protection
First, flood control should be considered as dictated by desig-
nation of the central Atchafalaya Basin for that purpose and by
regional stresses related to inadequacy of the present floodway. To
provide for immediate increase in flood-carrying capacity, the plan
proposes enlargement of the Main Channel from mile 55 to Wax Lake
Outlet through dredging to a bankfull cross-sectional area of approx-
imately 6500 m (70,000 ft/), or 7500 vf (80,000 ft2) when stated in
terms of area below project flow line. These dimensions are suggested
by the previous analysis of most probable dynamic equilibrium condi-
tions and are believed to closely approximate a channel dimension
that will be stable and self-maintaining under the prevailing Atcha-
falaya River regime if flow is partially confined by artificial levees.
Exceedence of those dimensions is believed to result in a need for
excessive maintenance dredging and associated spoil disposal unless
flow is totally confined for all possible discharges below project
flood magnitude through extension of such artificial levees as are
present above mile 55.
A reduction from the 9200 m2 (100,000 ft2) dimension.as pro-
posed by the U. S. Army Corps of Engineers, to 7500 m2 (80 000 ft2)
as proposed here,should be obtained by limiting the width to which'
the channel will be dredged. It is believed that in view of condi-
tions of prevailing discharges and sediment load, channel width
should be in the order of 410 m (1350 ft) to prevent-creation of an
underfit stream channel with resulting development of lateral chan-
nel bars. Channel flows should be confined to the largest extent
Possible,with diversion during normal years occurring only insofar
as required for maintenance of fish and wildlife resqurces. First,
this will fulfill the requirement for minimizing sedimentation in
overbank habitat. Secondly, this will insure to the greatest
extent possible full utilization of river energy in channel mainten-
ance and further enlargement if the self-maintaining cross-sectional
area proves to have been under-estimated.
159
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To achieve flow confinement as well as water-level control for
management of fish and wildlife resources, the plan first proposes
to utilize the dredging spoil for construction of continuous em-
bankments on both sides of the channel and to the largest possible
height permitted by the volume and nature of material available
through dredging to the proposed channel dimensions. Existing spoil
deposits should be considered as an additional source of material.
Secondly, it is proposed that all diversion through distribu-
taries from the Main Channel be controlled by structures and/or
navigation locks or by permanent closure where not essential to fish
and wildlife or navigational needs. More specifically and as shown
in Figure 9-2, diversion control structures are proposed at the
Atchafalaya River above Interstate 10 and at the East Freshwater
Distribution Channel, while permanent closure is recommended for the
West Freshwater Distribution Channel. Diversion control, with in-
clusion of provisions for navigation,is proposed for the East and
West Access Channels. These structures will be further discussed
in reference to fish and wildlife management strategies.
An additional complex of recommendations concerns the con-
veyance of floodwater from the floodway, across the Teche ridge,
toward the Gulf of Mexico. The plan (Figure i9-2) proposes three
major features which relate equally to flood control, flood pro-
tection, and navigation requirements. They are:
1) transformation of Wax Lake Outlet to the principal con-
tinuant route for all discharges from the floodway;
2) control over diversion of Main Channel flows past Morgan
City into the Lower Atchafalaya River; and
3) construction of a third, controlled outlet connecting the
western floodway with West Cote Blanche Bay.
At present, the apex of the Atchafalaya Delta may, in a sense,
be placed at the diversion of Wax Lake Outlet and the Main Channel
through Six Mile Lake, with each channel representing a major dis-
tributary. Inability of stream flows under the prevailing Atchafalaya
River regime to maintain the two channels at sufficient capacity was
discussed earlier. Confinement of non-flood flows to a single chan-
nel until reaching Atchafalaya Bay is believed to serve greatly the
objective of maintaining adequate capacity, maximizing at the same
time utilization or river energy.
For several reasons, Wax Lake Outlet has been selected as the
continuant Main Channel rather than the Lower Atchafalaya River. The
first reason relates to flood protection for the Morgan City area and
the Verret Basin. A decrease in high-water stages of the Lower
Atchafalaya River is required as a direct measure for protection of
Morgan City proper and as an indirect measure to ameliorate backwater
flooding of the Verret Basin and the Bayou Black levee ridges. The
160
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fltchofolQ/Q Basin. La.
SURFACE WATER MANAGEMENT
FLOOD CONTROL
Figure 9-2.
Proposed management of surface water for
multiple and compatible use of the Atchafalaya
Basin resources,
161
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second reason concerns the earlier-stated requirement to separate deep-
water access to Morgan City from the effects of delta building. Third-
ly, present trends are toward natural enlargement of Wax Lake Outlet
as a result of gradient advantages.
*
Associated with the flow routing through Wax Lake Outlet as the
principal outlet, a control structure is proposed at the diversion of
Wax Lake Outlet and the channel through Six Mile Lake leading toward
the Lower Atchafalaya River. The principal objective of this struc-
ture, hereafter referred to as the Six Mile Lake structure, is to
restrict flow diversion into the Lower Atchafalaya River and to pre-
vent a drastic reduction of its cross-sectional area through sedi-
mentation. Yet, it is anticipated that some diversion will be
necessary to provide partial abatement of salt water intrusion when
drainage from the East Floodway and the Verret Basin are at a mini-
muni.
The Six Mile Lake control structure would affect present Main
Channel navigation to and from Morgan City, but an alternative route
is available through the Intracoastal Waterway,which connects Morgan
City with the Wax Lake Outlet. The proposed provision for navigation
through the control structure,as indicated in Figure 9-2,is therefore
an alternative to rerouting of lower Main Channel navigation to the
Intracoastal Waterway.
Arising from the proposed partial separation of the West and
East Floodway from the Main Channel for water management purposes, and
with present outlet capacity being insufficient, a controlled and
leveed additional outlet in the form of a spillway and/or channel is
proposed. This outlet would serve the floodway west of the Main Chan-
nel for normal drainage as well as flood-routing to the Gulf. As in-
dicated in Figure 9-2, the outlet, hereafter referred to as the
Charenton Outlet, would parallel the present Charenton Canal and cross
Bayou Teche. Flow from the floodway into the outlet would be regulated
by a control structure to prevent excessive drainage of the West
Floodway during normal years. To prevent backwater flooding of the
Fausse Point Basin during outlet use for flood routing, separation of
the proposed Charenton Outlet from the Charenton Canal and Bayou Teche
is essential. A controlled connection with the Charenton Canal is
proposed, however, to provide for additional drainage-of the Fausse
Point Basin during periods of excessive runoff.
With regard to flood control and flood protection, the plan is
summarized schematically in Figure 9-3A for a condition of project
flood use. Water diverted from the Mississippi River through the Old
River control structure and Morganza Spillway and additional discharge
from the Red River routed into the Atchafalaya Basin Floodway conform
to present conditions. Within the floodway, exchange of water between
the Main Channel and the adjacent East and West Floodways remains
162
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FLOOD CONTROL
WATER MANAGEMENT
FISH & WILDLIFE
Figure 9-3. Schematic summary of water management plan. Diagram A shows operation
for project flood conditions; Diagram B shows operation during "normal"
years for environmental management. Structures primarily for flood
control are shown as rectangles, structures for environmental manage-
ment as stars.
-------
possible across the elevated banks below mile 55. Additional exchange
would be possible if needed through the proposed Six Mile Lake struc-
ture.
Discharge from the leveed floodway across the Teche ridge is
through three outlets, with Wax Lake Outlet the principal channel. The
second uncontrolled outlet is the Lower Atchafalaya River, which would
convey part or all of the East Floodway discharge. A third, con-
trolled outlet serves the West Floodway. Outlet capacities cannot be
specified here since necessary research would go far beyond the scope
of the present study. However, as a tentative approximation, capa-
cities of 21,250, 14,000 and 7,000 cms (750,000, 500,000 and 250,000
cfs) are envisioned for Wax Lake Outlet, the Lower Atchafalaya River,
and Charenton Outlet, respectively.
Management of the Fluvial Swamps
For management of the fluvial swamps within the floodway, the
plan recognizes three first-order hydrologic units: the Main Charinel,
the West Floodway, and the East Floodway. To achieve reduction in
sedimentation, sufficient annual dewatering, and improvement of water
quality, these three units are to become separate hydrologic entities
to the extent that .during normal flood years, water diversion from
the Main Channel into the East and West Floodways is controllable,
and dewatering of both floodway segments can occur independently of
Main Channel stages. Separation of the Main Channel from the East
and West Floodways would be achieved through the channel containment
as proposed for flood-control purposes in the previous section, with
necessary water diversion from the Main Channel taking place through
a number of control structures. Locations of these structures are
to be coincident with present and potential diversion channels and
dictated by individual second-order management units,as will be dis-
cussed further.
Outflow from the West and East Floodway is to be controlled as
well. The flood-control measures proposed in the previous section
allow dewatering independently of Main Channel stage, together with
control over the time and volume of outflow. Both would be achieved
by use of the controlled Charenton Outlet as the drainage channel
for the West Floodway. Outflow control with regard to the East
Floodway requires additional measures. While drainage of the East
Floodway under the plan proposed so far would be through the Lower
Atchafalaya River and virtually independent of Main Channel stages
as a result of the proposed Six Mile Lake control structure, no
control over time and volume,and consequently over water level, is
yet obtained. For that purpose, it is proposed that an embankment
be constructed along the northern side of Six Mile Lake connecting
the Main Channel levee with the East Floodway Protection Levee and
164
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containing a control structure with provision for navigation at the
entrance to the alternate route of the Intracoastal Waterway.
The proposed measures as discussed above essentially provide two
major basins with controlled input and output of river water and sedi-
ment and, therefore, controlled water level and water movement. With-
in each of these two basins, however, there are diverse requirements
as to absolute water levels related to characteristics of the various
management units. Obviously, a major difference in required absolute
water levels is inherent to the general southward slope of the basin
floor. Therefore, each of the two first-order basins is divided into
a series of second-order hydrologic units. Depending on water-level
requirements, these units are coincident with or combine individual
management units defined earlier in the report (Figure 2-3). To
achieve the stated water-management objectives, these second-order
hydrologic units or sub-basins also require control over inflow and
outflow.
Prior to detailing control at the management-unit level, the
plan can be schematically summarized as in Figure 9-3B. The diagram
shows the East and West Floodways as first-order hydrologic units,
each containing a series of second-order units. At the lower end of
both the East and West Floodways, a structure and continuant channel
provide for controlled outflow. A number of structures allow con-
trolled inflow from the Main Channel. As indicated by the solid lines,
second-order units are physically separated from each other by water-
level regulation levees that allow a certain maximum stage to be at-
tained within each unit. Inflow into individual second-order units
may be directly from the Main Channel and/or indirectly after routing
through an adjacent unit to the north in which required stages are
always higher. Control structures regulate outflow from each unit-
the outflow is received by the units to the south in a cumulative
process until discharged from the first-order drainage structure.
Management at Unit Level
In reference to Figure 9-2, management at the unit level may now
be discussed with regard to minimum diversion requirements and flow-
routing. The map shows actual second-order hydrologic units within
both the East and West Floodways. The hydrologic units combine those
management units having identical requirements as to minimum required
water level during flood stage,as indicated by the circled values
(peak swamp-stage). In the West Floodway, the Cocodrie Swamp and Beau
Bayou Management Units are combined, as are the West Atchafalaya
Floodway and Bayou Fordoche Management Units (Figure 2-3). In the
East Floodway, the most northern hydrologic unit combines the Morganza
Floodway and Alabama Bayou Management Unit and the Bayou des Glaises
Management Unit above Interstate Highway 10. The most southern
165
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hydrologic unit combines the Crevasse, Upper Belle River, and Flat
Lake Management Units,which all require a peak swamp-stage of 2.4 m
(8 ft) MSL.
As proposed, management of each hydrologic unit is achieved in
first instance through control over the flow directed into the major
channels bounding each unit. This is opposed to control over the ex-
change between water-supplying channels and individual sub-basins,
which would greatly hamper boat access to these sub-basins. Whereas
water supply thus would be controlled, the movement of water into the
swamp basins from adjacent channels, except the Main Channel, would
retain its present characteristics if no further measures were taken
to modify channel banks.
Following are the specific measures proposed with regard to
water supply and drainage for water management at the unit level.
First, the units within the West Floodway are discussed from north to
south. With regard to monthly water levels, proposed hydrographs are
those presented in the preceding part of this report dealing with the
unit topography and hydrographs (Chapter VII).
In the West Floodway, inflow for all units to the north of the
West Access Channel would be served by the Atchafalaya River, thus
requiring a first-order control structure at the diversion of this
river from the Main Channel. Channel size is judged sufficient to
supply all necessary water so that the West Fresh Water Diversion
Channel may be closed. Annual flooding of the Bayou Fordoche Manage-
ment Unit (Henderson Lake area) to a maximum of 4.8 m (16 ft) MSL
would occur through backwater flooding as presently occurs through
Bayou La Rose and the West Atchafalaya Basin borrow pit. Since
flooding of the Cocodrie Swamp and Beau Bayou Units is only needed to
a stage of 12 feet, a water regulation levee with an elevation of
4.8 m (16 ft) MSL would be required along the southern side of Bayou
La Rose,connecting the West Guide Levee and the high natural levee of
Little Atchafalaya River. A second-order control structure across
Little Atchafalaya River would provide for dewatering of the Bayou
Fordoche Unit as well as water input for the Cocodrie Swamp and Beau
Bayou Management Units. Commensurate requirements are closure of
Upper Grand River and Butte La Rose Cutoff.
A minimum peak swamp-stage of 3.6 m (12 ft) MSL is required in
common for the Cocodrie Swamp and Beau Bayou Units. This would demand
a water-level regulation levee the same elevation as that along the
northern side of the West Access Channel. The present spoil bank al-
ready attains or exceeds the 12-feet elevation. With water inflow
regulated at the proposed Little Atchafalaya River structure, a de-
watering control structure is required at the junction of the West
Access Regulation Levee and the West Guide Levee. Alternatively,
the structure may be placed in Lower Grand Bayou or Lake Fausse Point
166
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Cutoff, with closure of the other channel. If deemed desirable, back-
water flooding may be provided through the latter structure preceding
additional inflow from the Little Atchafalaya River structure.
The Buffalo Cove Management Unit requires a minimum peak swamp-stage of
2.7 m (9 ft) MSL. Proposed water input is through the West Access Chan-
nel by means of a control structure at its diversion from the Main Chan-
nel. Dewatering would be served by the Charenton Outlet.
In the East Floodway, a similar strategy of flow routing is
followed. Beginning with the most northern unit, Bayou des Glaises
a water-level regulation levee parallel to Interstate 10 is necessary
since required water levels to the north of Interstate 10 exceed those
??***% 8£«h cy ;06 m ( 2 ft>- T° Provide for annual flooding to 4.8 m
(16 ft) MSL of the northern Bayou des Glaises Unit, there are two al-
ternatives. The first is through the presently planned Alabama Bayou
structure near Krotz Springs. The second is through backwater flooding
ll°T±l e ? T8^6 ° ?°T rUCti°n Cana1' In the flrst case> as show?
in Figure 9-2 the regulation levee is to be placed north of the Inter-
state 10 canal, utilizing either abandoned railroad embankment or the
canal spoil deposits. The levee should have a crest elevation of 4.8 m
(16 ft) and contain a dewatering control structure across Bayou des
Glaises. '
If backwater flooding is determined to be more desirable, inflow
for both the northern and the southern parts of the Bayou des Glaises
Unit can be served at once by a control structure at the presently
closed intersection of the Interstate 10 construction canal and the
Main Channel. The water- regulation levee should then be placed to the
south of Interstate 10 and contain a control structure across the canal
leading from the Interstate 10 construction canal southward to the East
Freshwater Distribution Channel.
The plan provides for flooding of the southern Bayou des Glaises
Unit to 4.2 m (14 ft) MSL through a proposed control structure at the
junction of the Interstate 10 canal and the Main Channel as referred to
above. A water-level regulation levee is required along the northern
bank of the East Freshwater Diversion Channel, with a crest elevation of
4.2 m (14 ft) and containing a second -order control structure to regu-
late dewatering. As proposed, the structure is located at the junction
In the Bayou Pigeon Unit, the management requirement is for annual
flooding to a stage of 3.3 m (11 ft) MSL. It is proposed that water be
supplied through the East Freshwater Diversion Channel as occurs at
present, with diversion from the Main Channel regulated by a control
structure. Adjacent units to the south require a peak swamp stage of
only 2.4 m (8 ft) MSL. A water-regulation levee is necessary along the
southern margin of the Bayou Pigeon Unit; that is, along the East Access
167
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Channel so that existing spoil deposits can be utilized. The embankment
should contain a second-order structure, which would be located at the
,-East Guide Levee borrow-pit, for dewatering.
The hydrologic entity composed of Upper Belle River, the Crevasse,
and Flat Lake Management Units has an annual flood-stage requirement of
2.4 m (8 ft) MSL. As at present, water would be supplied by the West
Access Channel, but with a provision for inflow control by means of a
structure. The proposed embankment along the northern side of Six Mile
Lake and the associated structure at the Intracoastal Waterway that
were discussed earlier would serve stage regulation and dewatering,
respectively.
Inherent to the proposed structural measures is a constraint on
navigation. Navigation locks proposed at the East and West Access
Channels and at the Intracoastal Waterway provide for cross-basin
navigation, and unrestricted access to the East and West Floodways
south of the access channels. However, proposed secondary water-man-
agement structures would prevent navigation from crossing boundaries
of the four hydrologic units to the north. This does not necessarily
cause a major conflict with regard to small-boat traffic related to
commercial and sports fisheries since boat ramps presently provide for
access to each of these units. Larger craft, such as associated with
the mineral industry, must, however, be taken into consideration. Where-
as further evaluation of this problem is necessary in regard to precise
requirements, possible solutions other than a multitude of navigation
locks are available. Boats and barges required for maintenance of oil
fields may be stationed permanently within hydrologic units. Since
roads provide access to the guide levees, construction of dock facili-
ties could provide for transfer of heavy equipment onto barges. Earthen
dams may be constructed adjacent to secondary water-management struc-
tures and be temporarily removed to allow passage of drilling rigs,
which is an infrequent event.
So far, the questions of water movement from the supply channels
into adjacent swamp basins and that of volume of water to be diverted
to fulfill requirements of individual management units have been
tacitly ignored. Previous studies identified various circulatory con-
ditions leading to insufficient water circulation and water quality
problems.182, 183 p-rom this, it appears a throughflow regime or a
combination of head and backwater flooding are the regimes most de-
sirable; that is.where annual flooding provides for water input across
the upper margin of a basin,forcing water to move through the swamp as
a result of the general north-to-south gradient. This is opposed to a
182 Coastal Environments, Inc., 1974a, op. cit.
'Coastal Environments, Inc., 1974b, op. cit.
168
-------
condition where water enters predominantly from the side and lower end,
resulting in stagnation and insufficient annual replacement of water
in the upper and central parts of the basin.
In accordance with the above point of view, the proposed plan
renders the possibility to provide maximum circulation for a given
volume of water input. With one exception, water is supplied at the
upper end of the units ,and drainage is across the lower margin. Addi-
tional measures should be taken, however, to ensure water iJput across
the upper margin of individual units. across
n SUpply channel banks forming the upper
?* S " * are nearly conti™°"s ^d elevated by spoil
deposits. Where this is the case, provisions should be made to allow
inflow across these banks in a manner resembling natural overbank
STSStScSS S "jr*?,-, Preferably> thi.8-y be ac'mplisld by
s:e: : -y^ ^.I-SX-K^^S^
distribution system along the upper margin of the unit
The mentioned exception to: the proposed throughflow regime con-
* lesser circulation associated
with a backwater regime.
An additional reason for supplying water to the upper end of each
unit relates to river gradient. It ensures maximum availability of
water during low-river stages, in either low-discharge years or durlnjr
summer months, for reasons of forcing water circulation through the
avambiri/drainari'6,3/681^16 -»*—* st™tegy *l£ becomes
available if drainage is independent of Main Channel stage as proposed
Simultaneous operation of inlet and outlet structures caJ be used^o
produce a limited flushing of both the East and West Floodway systems.
The question of volume of water to be diverted to fulfill re-
quirements of individual management units may be addressed using
Figure 9-4. The diagram is a schematic representation of the floodwav
management units. Units are identified as follows: "oodway
184 Ibid.
169
-------
2920
r
<
EC
m
c
fc
Q
fc
UJ
940
W3
o
CO
CM
CM
4000
UJ
z
z
<
u
UJ
u
6000
UJ
Figure 9-4, Schematic representation of floodway management units and
water routing. Values represent highest monthly discharge
for minimum water requirements,
170
-------
West Floodway Units East Floodway Units
Wl West Atchafalaya Floodway E1 Morgans Floodway
W2 Bayou Fordoche E2 Alabama fiayou
W3 Warner Lake E3 Bayou deg
W4 Cocodrie Swamp E4 pigeQn
W5 Beau Bayou E5 Flafc
W6 Buffalo Cove E6 Crevasse
W7 Six Mile Lake E7 Upper Belle
Ead] unit is considered as an entity with a respective point of
inflow and outflow. It is further assumed that full control is exer-
cised over the entire range of discharges at all inlet and outlet
structures and that excess water is discharged into the next lower unit.
Within the above framework and utilizing storage characteristics of
each unit, one can determine on a monthly basis river-water supplements
required to attain given target stages within each unit. Target; stages
Sd
Utilizing the water-resources data and methods described in
previous chapters, water budgets were developed for each management
unit for average conditions and for a monthly time unit. Tables 9-1
and 9-2 show the results for the West and East Floodways, respectively
For each unit in the tables, the following values are listed:
Target Stage (TS) Target mean water level of management unit
in feet ;
Storage Required (SR) Volume of water in storage below target stage
in million cubic feet (mcf);
Upstream Flow (UF) input from upstream management unit in mcf;
Local Yield (LY) Input from runoff within unit in mcf;
Total Inflow (Ti) Sum of upstream flow and local yield in mcf;
EXC6SS (EX) Water ln excess of storage requirement in mcf;
Deficiency (DE) Supplemental water required to satisfy stor-
age requirement in mcf.
171
-------
Table 9-1. Water Budget, Regulated Management Units, West Atchafalaya Floodway.
NJ
Total
Total
TS
TS
BAYOU FORDOCHE
SR
UF
IL
October
November
December
January
February
March
April
May
June
July
August
September
10.9
11.1
12.9
15.1
15.7
16.5
17.4
17.5
15.6
12.9
12.2
10.8
4600
4800
8000
13100
14600
16400.
18700
19000
14300
8100
6500
4400
86
408
1365
2026
1863
1333
950
742
167
106
0
4
-31
396
984
1148
1163
749
246
-63
-577
-198
-380
-283
55
804
2349
3174
3026
2082
1196
679
-410
-92
-380
-279
604
1526
282
379
4290
6108
1220
1821
9050
3154 12204
COCODRIE SWAMP
SR
LY II
16230
1710
18040
DE
145
851
1926
1104
16230
EX
October
November
December
January
February
March
April
May
June
July
August
September
6.2
6.0
8.1
10.4
11.2
13.4
15.7
15.2
12.2
8.7
7.0
5.6
600
500
1200
2200
2700
4400
6900
6300
3400
1400
800
400
604
1526
282
379
4290
6108
1220
1921
62
123
423
478
502
326
67
-104
-182
60
-16
-29
62
727
423
478
2028
608
67
275
4108
6168
1204
1892
827
1528
875
7008
8168
1804
2292
4026
DE
138
277
522
1092
2433
22502
4462
-------
Table 9-1. (continued). Water' Budget, Regulated Management Units, West Atchafalaya Floodway.
BEAU BAYOU
10
Total
TS
TS
SR
UF
LY
TI
EX
October
November
December
January
February
March
April
May
June
July
August
September
5.0
4.6
6.7
8.5
9.3
11.8
14.4
13.6
10.6
7.1
5.3
4.2
200
200
600
1100
1400
2700
4400
3900
2100
700
200
100
827
1528
875
7008
8168
1804
2292
35
62
236
266
282
180
27
-75
-122
23
1
-3
35
889
236
266
1810
180
27
800
6886
8191
1805
2289
889
\j\jy
1510
1300
8686
9591
2305
2389
DE
65
164
235
1120
1673
SR
22502 912 23414
BUFFALO COVE
UF LY II
26670
EX
3256
DE
October
November
December
January
February
March
April
May
June
July
August
September
4.0
3.7
5.0
6.4
6.8
8.7
10.7
10.3
8.0
5.4
4.2
3.5
300
300
100
600
900
1900
4000
3300
1400
400
300
200
Total
889
1510
1300
8686
9591
2305
2389
26670
102
190
762
699
730
399
-208
-717
-903
-267
-202
-173
413
102
1680
762
699
2240
399
-208
583
7783
9324
2103
2216
27083
2
1085
962
199
1940
1283
9683
10324
2203
2316
29992
601
2308
2909
-------
Table 9-2. Water Budget, Regulated Management Units, East Atchafalaya Floodway.
BAYOU DBS GLAISES
October
November
December
January
February
March
April
May
June
July
Augus t
September
Total
October
November
December
January
February
March
April
May
June
July
August
September
JTS
4.8
4.0
6.0
7.9
8.7
11.5
14.4
13.5
10.8
6.8
5.0
4.0
JTS
4.4
4.0
5.8
7.4
8.1
10.4
12.6
11.9
9.4
6.2
4.7
3.8
J5R
200
100
400
1000
1500
4400
9400
7700
3500
600
200
100
JR
200
100
700
1600
2100
4400
7200
6300
3300
900
300
100
UF
56
401
1163
1602
1554
1086
680
497
21
122
7182
UF
6
668
1445
1817
1922
2114
3878
3080
430
118
LY
50
167
582
815
868
618
172
-83
-343
58
30
18
2952
PIGEON BAY
LY
125
105
465
242
471
292
20
-182
-198
115
40
4
XI
106
568
1745
2417
2422
1704
852
414
-312
180
30
18
10134
TI
131
773
1910
2059
2393
292
20
1932
3680
3195
470
122
EX
6
668
1445
1817
1922
2114
3878
3080
430
118
15478
J2X
31
873
1310
1159
1893
2832
6680
5595
1070
322
DE
1196
4148
5344
DE
2008
2780
Total
15478
1499
16977
21765
4788
-------
Table 9-2. (continued),
VI
Ol
October
November
December
January
February
March
April
May
June
July
August
September
Total
TS
TS
Water Budget, Regulated Management Units,.East Atchafalaya Floodway.
FLAT LAKE
SR
UF
LY
TI
EX
3.2
2.8
3.9
5.0
5.4
7.1
8.8
8.3
6.5
4.3
3.3
2.8
1100
800
2000
3600
4200
7100
10200
9300
6500
2500
1200
800
31
873
1310
1159
1893
2832
6680
5595
1070
322
-66
308
679
577
650
461
133
-142
-437
-150
-231
-6
-35
1181
1989
1736
2543
401
133
2690
6243
5495
839
316
1481
789
136
1943
3590
9043
9445
2139
716
DE
335
2439
SR
21765 1776 23541
THE CREVASSE
UF LY TI
29282
EX
5741
DE
October
November
December
January
February
March
April
May
June
July
August
September
2.0
1.8
2.2
2.8
3.2
4.2
5.5
5.2
4.1
2.8
2.2
2.0
800
700
900
1200
1500
2200
3600
3200
2100
1200
900
800
1481
789
136
1943
3590
9043
9445
2139
716
7
180
439
570
525
377
224
91
-144
-97
-131
-74
7
1661
1228
706
2468
377
224
3681
8899
9348
2008
642
7
1761
1028
406
2168
4081
9999
10248
2308
742
323
1176
Total
29282
1967
31249
32748
1499
-------
Table 9-2. (continued). Water Budget, Regulated Management Units, East Atchafalaya Floodway.
UPPER BELLE RIVER
October
November
December
January
February
March
April
May
June
July
August
September
TS
2.0
1.8
2.2
2.8
3.2
4.2
5.5
5.2
4.1
2.8
2.2
2.0
SR
2500
2000
3100
5500
7300
12300
19000
17400
11800
5500
3100
2500
UF
7
1761
1028
406
2168
4081
9999
10248
2308
742
LY
149
749
1798
1589
1708
897
110
-905
-1453
-492
-642
-282
TI
156
2510
2826
1995
3876
897
110
3176
8546
9756
1666
460
EX
156
3010
1726
2076
4776
14146
16056
4066
1060
DE
405
4103
6590
Total
32748
3226
35974
47072
11098
-------
For each regulated unit, total inflow from an upstream unit and local
rainfall in excess of the need for a particular month are released to
the downstream unit. Water deficiency is satisfied by withdrawal from
a water-supply channel. Under this scheme, maximum use is made of the
fresh water developed from local rainfall. Some statistics of interest
are generated from input of normal monthly water yield into the water
management model. Tables 9-3 and 9-4 summarize supplemental and re-
turn-flow requirements, along with corresponding normal monthly flow
volumes of the Atchafalaya River at Simmesport, Louisiana. It may
be noted that the total flow requirement of the floodway swamps under
this management plan is a negligible fraction of water normally avail-
able in the Main Channel. Consequently, discharge capacity require-
ments for each branch of the model are small. These requirements
are shown in Figure 9-4 as developed by converting the maximum monthly
volumes of excess and supplemental flows of Tables 9-3 and 9-4 into
mean cubic feet per second.
It should be emphasized that a plan of operation and design
should take into-account additional factors. Target stages may need
to be revised if more data become available on water-level require-
ments. Also, additional input of water may be necessary to force
circulation during months when water-quality problems are likely to
arise. Several refinements of analysis techniques could be employed
in a more comprehensive study. The most important refinement is the
inclusion of simulation trials conducted on the water-management model.
Such trials should cover many years of meteorological data to ascer-
tain how the system reacts during extremely wet and dry periods and
enable adjustment of the parameters of the system to handle varia-
tions from normal conditions.
Management of the Coastal Area
While complexity of problems in the coastal area did not permit
development of a comprehensive management strategy for that area, some
specific recommendations can be made and are integrated into the pro-
posed plan (Figure 9-2). These are for Wax Lake Outlet to become the
principal extension of the Main Channel and for containment of delta
growth associated with the discharge of water and sediment from the
outlet.
With regard to flood protection and navigation for the Morgan
City area, the reasons for making Wax Lake Outlet the principal chan-
nel were already stated. There is an additional reason when consider-
ing present diversion of river water and sediment into the Terrebonne
marshes Even though the benefit of such sedimentation as a measure
to offset land loss is fully appreciated, it may be more desirable to
offset land loss by new delta building than to attempt restoration of
the marsh system in its present state. Under the proposed plan with
177
-------
Table 9-3. Summary of Supplemental Flow Requirements, Million Cubic Feet.
00
OCX
NOV
DEC
JAN
FEB
MAS
APR
MAY
JUN
JUL
AUG
WEST FLOODWAY
SEP
TOTAL
W2
W4
W5
W6
Total
145
138
65
348
851
277
164
1292
1926
522
234
2682
1092
1120
601
2813
1104
2433
1673
2308
7518
4026
4462
3256
2909
14653
EAST FLOODWAY
E3
E4
E5
E6
E7
Total
Grand
Total
Simmesport
Flow, BCF
2 Div.
835
835
1183
209
0.57
220
1292
335
0.39
405
405
3087
445
0.69
522
1196
2008
2439
323
4103
10069
12882
729
1.77
4148
2780
2967
1176
6590
17661
25179
822
3.06
785
581
437
273
194
5344
4788
6241
1499
11098
28970
43623
5554
0.78
-------
Table 9-4. Summary of Return Flows, Million Cubic Feet.
October
November
December
January
February
March
April
May
June
July
August
September
TOTAL
W. Fwy.
2
1080
962
199
1940
1283
9683
10324
2203
2316
29992
E. Fwy.
156
3010
1726
'2076
'4776
14146
16056
4066
1060
47072
Total
158
4090
2688
4016
6059
23829
26380
6269
3076
77064
Net
Gain
-428
4090
1396
-3795
4016
-25238
5274
23248
25943
5996
2882
33423
Net
Loss
1025
2888
12882
25179
% of
Simmesport
-0.49
1.86
0.42
-0.65
0.77
-1.77
-3.06
0.67
4.00
5.94
2.20
1.49
0.60
179
-------
reduced flows through the Atchafalaya River, a transition to more
saline conditions would occur, and a gradual increase in the length
of land-water interface in the marsh system would result through
natural processes of subsidence and wave erosion. As experienced in
other areas along the Louisiana coast, such as Barataria Bay, a highly
productive brackish-to-saline estuarine environment can be expected
to evolve. ^°^ Commensurate development of the delta in Atchafalaya
Bay will produce a new freshwater environment adjusted to the varia-
tion in river discharges under which it develops. Such a process of
commensurate gain and loss would be a replication of former natural
processes along the Louisiana coastal zone prior to man's interference
with the natural sequence of deltaic development and deterioration.
While a forced transition of the Terrebonne marshes to more
saline conditions is viewed as a viable possibility, this would re-
quire additional measures in order to prevent rapid deterioration
through saltwater intrusions. Commensurate with decreasing Lower
Atchafalaya River discharges, provisions should be made to make full
use of Verret Basin runoff as a source of fresh water for management
of the salinity regime.
Management of delta growth through containment is proposed as
a necessary measure to protect the Cote Blanche Bay system to the east
and to fulfill navigation requirements. Under the proposed plan,
sediment would be discharged primarily from the Wax Lake Outlet, and
shallowness of Atchafalaya Bay must be expected to produce a broad
delta front. Thus, even though the delta apex would be displaced
westward, delta progradation would still block deep-water access to
the Lower Atchafalaya River. For this reason, it is proposed that an
embankment be constructed limiting eastward growth of the delta.
Present spoil deposits along the Atchafalaya Bay navigation channel
could be utilized, while additional material for the embankment could
be obtained through dredging necessary to bring the navigation channel
again to its authorized depth.
A second delta containment bank is proposed along the west side
of the developing delta to protect the Cote Blanche Bay estuarine
system from excessive sedimentation and infilling. Material for the
western embankment could be derived from dredging necessary to enlarge
the Wax Lake Outlet to proposed dimensions.
The plan for multi-use management of the Atchafalaya Basin as set
forth here still leaves many questions unanswered. Complexity of
problems in the coastal area did not allow specification of require-
ments sufficient for detailed plan-development. Equally, the paucity
185Gagliano elt al., 1973, o£. cit.
180
-------
of topographic and other baseline data hampered development of detailed
recommendations for the Fausse Point and Verret Basin. On the other
hand, it must be pointed out that care was taken not to foreclose any
identified options for management of both the coastal area and the
basins adjacent to the floodway insofar as these options could be re-
conciled with the overriding requirements for flood control.
For the Atchafalaya Basin Floodway, it is believed that the plan
achieves many of the objectives of this study in that it provides for
a means of flood control that minimizes environmental impact and guards
long-term benefits of the Atchafalaya Basin for both exploitative and
protective uses.
181
-------
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196
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APPENDIX A
Louisiana Mammals Whose Range Includes the Atchafalava Basin
Opossums
Virginia opossum (Didelphis virginiana)
Shrews
Short-tailed shrew (Blarina brevicauda)
Least shrew (Cryptotis parya)~
Bats
Southeastern myotis (Myotis austroriparius)
Eastern pipistrelle (Pipistrellus subflavus)
Big brown bat (Eptesicus fuscus)
Red bat (Lasiurus borealis)
Seminole bat (Lasiurus seminolus)
Hoary bat (Lasiurus cinereus)
Northern yellow bat (Lasiurus intermedius)
Evening bat (Nycticeius humeralis)"
Rafinesque's big-eared bat (Pleeotus rafinesquii)
Brazilian free-tailed bat (Tadarida brazilienais)
Armadillos
Nine-banded armadillo (Dasypus novemcinctus)
Rabbits
Eastern cottontail (Sylvilagus floridanus)
Swamp rabbit (Sylvilagus aquaticusl
Rodents
Gray squirrel (Sciurus carolinensis)
Fox squirrel (Sciurus niger)
Southern flying squirrel (Glaucomys volans)
American beaver (Castor canadensis)
Marsh rice rat- (Oryzomys palustris)
Eastern harvest mouse (Reithrodontomva humulis)
Fulvous harvest mouse (Reithrodontomys fulvescens)
White-footed mouse (Peromyscus leucopus)
Cotton mouse CPeromyscus gossypinus)
Hispid cotton rat (Sigmodon hispidus)
Eastern wood rat (Neotoma floridana)
197
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Common muskrat (Ondatra zlbethicus)
Roof rat (Rattus rattus)
Norway rat (Rattus norvegicus)
House mouse (Mus musculus)
Nutria (Myocastor coypus)
Carnivores
Coyote (Canis latrans)
Red fox (Vulpes fulva)
Gray fox (Urocyon cinereoargenteus)
Black bear (Euarctos americanus)
Northern.raccoon (Procyon lotor)
Long-tailed weasel (Mustela frenata)
North American mink (Mustela yison)
Striped skunk (Mephitis mephitis)
Nearctic river otter (Lutra canadensis)
Bobcat (Lynx rufus)
Deer
White-tailed deer (Odocoileus virginianus)
198
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APPENDIX B
Annotated List of Some Common and Rare Birds
of the Atchafalaya Basin
Heronlike Birds
Herons and Egrets
These are common birds in swamp and marsh habitats, and usually
several species may be seen on nearly every outing into the basin.
Commonly observed species include the great (American) egret, snowy
egret, Louisiana heron, little blue heron, and green heron. Less fre-
quently seen are the great blue heron and the yellow-crowned night
heron.
Storks
The wood stork is fairly common in the swamps of the basin dur-
ing the summer, although it apparently does not nest there.
Ibises
The white ^is is common in the basin. It is most often observed
Herons, ibises, and wood storks feed mostly on small fishes,
£££££?
-------
hawk is mostly a summer resident in wooded areas. The red-tailed hawk
is most abundant in the winter in cleared areas. The marsh hawk oc-
curs in agricultural fields and in marshes in the winter.
The Mississippi kite is abundant in the basin as a summer resi-
dent. The swallow-tailed kite also occurs here during the summer, but
is rare.
The American kestrel (sparrow hawk) is a common winter resident
in cleared areas of the basin.
Besides the above-mentioned birds, the following species are rare.
Osprey
The osprey is an uncommon or rare summer resident. A fish eater,
it may be expected to occur in the Lake Verret and Grand Lake/Six Mile
Lake area and near other large lakes in the basin.
Southern Bald Eagle
The bald eagle occurs in scattered areas in south Louisiana where
it nests in the winter. A recently occupied bald eagle nest is ap-
proximately 25 miles southeast of Morgan City. Also a fish eater, this bird
may be expected in the vicinity of large lakes. The southern bald
eagle is currently listed as an endangered species.
Peregrine Falcon
The peregrine falcon is an endangered species which occurs in
the marshes in the lower basin.
Fowl-Like Birds
Quail and Turkey
The bobwhite quail occurs throughout the basin except in the
marshes. Quail exist in the swamp and bottomland hardwoods areas in
low numbers. Barely huntable populations of quail occur in the cleared
farmlands in the upper basin.
Wild turkeys may have originally occurred as a natural popula-
tion in the higher forested areas of the basin. The present turkeys,
however, have been introduced into Pointe Coupee and Iberville Parishes.
200
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Crane-Like Birds
Rails
Clapper rails occur in the more saline marshes in the lower
basin. The king rail prefers the fresher marshes, lake shores, and
drainage ditches in wet fields. These birds are year-round residents,
The Virginia rail, sora, and yellow rail occur in fresh marshes and
wet, grassy fields and are winter residents.
Gallinules
, ^ ^PU2levan,d C°T°n 8allinules occur mostly in the summer. They
inhabit the banks of bayous, ponds, and lakes in the swamps and marsh.
Coots
The coot, or poule d'eau as it is called in Louisiana, is abundant
on lakes and ponds throughout the basin in the winter. A few coots re-
main in the basin in the summer. The coot is a popular game bird in
south Louisiana.
Shore Birds
Plovers
Most of the plovers in Louisiana are found in the immediate
coastal area on beaches and exposed tidal flats. The killdeer is an
exception and it is usually common the year around (abundant in win-
- inland cleared areas, such as fields, golf courses, and levees.
Sandpipers
The most outstanding birds among this group in the basin are the
game birds ~ the American woodcock and the common snipe. The wood-
cock occurs most abundantly in the winter. It feeds -at night in agri-
cultural fields and cleared areas on earthworms or otnergSund- *
So i^hJr? T f d/eeks COVer durin8 the day m forested areas.
The Atcnafalava Basin Is an -tmnn-^t-^t- ,~»_j j «. «»*.««».
resident and has similar £ood ^bits> alth(n;gh tt
201
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Besides the woodcock and snipe, the upland, spotted, and soli-
tary sandpipers may be observed at inland localities near farmlands,
while the willet, the pectoral sandpiper, and the least sandpiper are
most often seen on marsh mudflats and beaches.
Gulls and Terns
These birds may occasionally be observed in inland areas, par-
ticularly near large rivers, but they are usually strictly coastal
birds. Herring gulls and laughing gulls are common from Morgan City
southward. The laughing gull is a year-round resident, while the
herring gull is usually absent in the summer. The ring-billed gull
is a common winter resident in the coastal area.
Six kinds of terns are fairly common on the coast. The Forster,
royal, and Caspian terns are permanent residents; the black tern and
the least tern are summer residents, while the gull-billed tern is
present in the winter.
Skimmers
The black skimmer is a common coastal bird which frequents the
Gulf beaches and islands in bays.
Pigeon-Like Birds
Besides the domestic pigeon, which is abundant in Morgan City,
the mourning dove is the only species in this group which is common.
It is a game species which occurs year-round in the basin, mostly in
and near farmlands. Dove populations are greatly increased in the
winter when large numbers of migrating doves come in from the north.
Huntable numbers of doves occur in the winter in the farmlands in the
northern end of the basin.
Owls
At least three species of owls are common in the basin: the
great horned owl, the barred owl, and the screech owl. The barn owl
is probably also common in the cleared areas to the north. Of the
three common species, the barred owl is undoubtedly the most abundant.
Owls occur throughout the wooded areas of the basin,*and they may
often be seen roosting is treetops during the daytime near Interstate
10 and U. S. Highway 190. Barred owls are frequently struck by cars
and killed along the non-elevated portions of highways in and around
the basin.
202
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Owls are top carnivores, feeding mostly on small mammals. They
also feed on insects, lizards, crawfishes, fishes, and small birds
The nocturnal hooting of owls is a characteristic sound in the Atchafa-
laya Basin swamp.
Kingfisher
The belted kingfisher is one of the most characteristic birds of
the swamp and is familiar to most sportsmen and hunters. The king-
fisher has a habit of flying ahead of a running boat in bayous, usually
for a short distance, but often for a mile or two. It is also fre-
quently seen perched on telephone wires along a roadside canal, waiting
for a small fish to appear near the water surface. Small fishes make
up the largest part of its diet, which also includes insects and small
frogs. The kingfisher is a year-round resident in the swamps and
marshes of the basin.
Woodpeckers
Six woodpeckers are found in the Atchafalaya Basin: the flicker,
the red-bellied woodpecker, the pileated woodpecker, the hairy wood-
pecker, the.downy woodpecker, and the yellow-bellied'sapsucker. All
of the woodpeckers, except the last-named species (which is present in
the winter months), are permanent residents and are fairly common. The
pileated woodpecker, due to its large size and striking appearance, is
perhaps the species most frequently observed by the average sportsman
in the basin. The pileated woodpecker resembles, in general body form
and to some degree in coloration, the endangered (or extinct?) ivory-
billed woodpecker, which could possibly occur in certain areas of the
187 Indeed» the mature, climax live oak - mixed hardwood for-
ests in the vicinity of Cypress and Tiger Islands in the lower basin
would appear to be excellent wildlife habitat in general and prime
ivory-billed woodpecker habitat. Every effort should be made to pre-
serve these forests, since they are an endangered habitat type in the
south.iab
186
'• <£T£d Nfin' "™e Irreslstlble» Elusive Allure of the Ivory-
Smithsonian (Volume 4, No. 11, 1974).
187.. _ _
U. S. Department of the Interior, 1974, op_. cit., p. 77.
IMI.,™* ^ichard K. Yancey, "The Vanishing Delta Hardwoods: Their
Wildlife Resources," (Presentation to the Governor's Seminar on the
Mississippi Delta Hardwoods, Little Rock Arkansas, 1969)
203
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Perching Birds
This large order is well-represented in the basin. Some of the
more common and well-known species include the following.
Permanent Residents
Forested areas: blue jay, common crow, Carolina chickadee, brown
thrasher, common yellow throat, red-winged blackbird, common grackle,
cardinal.
Cleared areas, including towns: blue jay, common crow, mocking-
bird, brown thrasher, loggerhead shrike, starling, house sparrow, east-
ern meadowlark, red-winged blackbird, common grackle, brown-headed
cowbird, cardinal.
Marshes: common crow, fish crow, long-billed marsh wren, logger-
head shrike, red-winged blackbird, eastern meadowlark, common grackle,
boat-tailed grackle, seaside sparrow.
Summer Residents
Forested areas: Acadian flycatcher, wood thrush, white-eyed
vireo, red-eyed vireo, prothonotary warbler (this is one of the most
common birds in the swamp areas of the basin in the summer; it is
well known to local residents as simply the "yellow bird"), Kentucky
warbler, hooded warbler, orchard oriole, summer tanager, painted bunt-
ing (this highly colorful bird is also well known to local residents
as the "pop," or "papa").
Cleared areas, including towns: eastern kingbird, purple martin,
orchard oriole, Baltimore oriole, summer tanager.
Winter Residents
Forested areas: eastern phoebe, hermit thrush, ruby-crowned
kinglet, cedar waxwing, yellow-rumped (Myrtle) warbler, rufous-sided
towhee, white-throated sparrow, swamp sparrow.
Cleared areas, including towns: tree swallow, American robin,
ruby-crowned kinglet, cedar waxwing, rusty blackbird, Brewer blackbird,
rufous-sided towhee, white-throated sparrow.
204
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TECHNICAL REPORT DATA
(Please read Instructions on the reverse before completing)
1. REPORT NO.
EPA-600/3-77-062
4. TITLE AND SUBTITLE
PLAN AND CONCEPTS FOR MULTI-USE MANAGEMENT OF THE
ATCHAFALAYA BASIN
3. RECIPIENT'S ACCESSION-NO.
6. REPORT DATE
May 1977
6. PERFORMING ORGANIZATION CODE
7. AUTHOR(S)
Johannes L. van Beek, William G. Smith, James W.
Smith, and Philip Light
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
Coastal Environments, Inc.
1260 Main Street
Baton Rouge, Louisiana 70802
10. PROGRAM ELEMENT NO.
1BD613
11. CONTRACT/GRANT NO.
68-01-2299
12. SPONSORING AGENCY NAME AND ADDRESS ~
U.S. Environmental Protection Agency-Las Vegas, NV
Office of Research and Development
Environmental Monitoring and Support Laboratory
Las Vegas, Nevada 89114
13. TYPE OF REPORT AND PERIOD COVERED
Final Jan. 1975-Aug. 1976
14. SPONSORING AGENCY CODE
EPA/600/07
16. SUPPLEMENTARY NOTES
The report determines surface water requirements of the natural resource complex,
including fishes, wildlife, and forests, and the- socio-economic resource uses,
including flood control, urban and industrial development, mineral extraction,
transportation, agriculture, and recreation. Requirements are expressed in terms of
desirable annual water-level variation, and resulting hydrographs are compared with
those for present and proposed conditions associated with channelization. Minimum
volumetric inflow requirements were calculated on the basis of storage characteris-
tics and water levels as attained at present. Hydraulic geometry of the present main
river channel is analyzed, and those channel dimensions that are in equilibrium with
bankfull discharge suggest that channel enlargement through dredging should not go
beyond a cross-sectional area of 7,400 square meters.
A surface-water management plan is presented that is believed to provide for
maximum longevity of the remaining swamp ecosystem, to minimize the conflict arising
from flood-control needs, and to make possible compatible derivation of benefits from
both renewable and non-renewable resources.
7.
KEY WORDS AND DOCUMENT ANALYSIS
DESCRIPTORS
b.IDENTIFIERS/OPEN ENDED TERMS
c. COSATI Field/Group
*Water resources development
Runoff
Water quality
*Flood control
Sedimentation
Forestry
*Wildlife
*Hydrography
Deltas
Swamps
Atchafalaya Basin
Wetlands
Water management
Channel stabilization
Crawfish
02 F
08 A, F, H
13 B
8. DISTRIBUTION STATEMENT
RELEASE TO PUBLIC
19. SECURITY CLASS (ThtiReport)'
UNCLASSIFIED
21. NO. OF PAGES
218
20. SECURITY CLASS (Thispage)
UNCLASSIFIED
22. PRICE
EPA Form 22ZO-1 (8-73)
GOVERNMENT PRINTING OFFICE: 1977 - 784-819/125 Region No. 9-1
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