THE CONTROL OF POLLUTION
FROM
HTDR06RAPHIC MODIFICATIONS
UNITED STATES
ENVIRONMENTAL PROTECTION AGENGT
Washington, D.C. 20460
1973
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FOREWORD
Degradation of the quality of fresh surface and ground
waters caused by hydrographic modifications such as stream
channel alterations or the impoundment of water is a common
problem as man alters his environment. Such pollution is
frequently an unintentional result associated with these
activities.
The Federal Water Pollution Control Act, as amended
(33 U.S.C. 1251 et seq.; 86 stat. 816 et seq.; P.L. 92-500)
requires the Administrator of the Environmental Protection
Agency to issue information on the identification and control
of pollution caused by hydrographic modification (section
304(e)(l&2)(F)). This report is issued pursuant to that
legislative mandate.
Russell E. Train
Administrator
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THE CONTROL OF POLLUTION CAUSED BY
HYDROGRAPHIC MODIFICATIONS
LIBRARY
Environ. Prot. Agency, WQO
Etflson, New Jersey 08817
For sale by the Superintendent of Documents, U.S. Government Printing Office, Washington, D.C. 20402 - Price $1.05
U. S. Environmental Protection Agency
Uashington, D. C. 20460
1973
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TAi3LL OF CONTENTS
I.
Heading
Foreword
Taule of Contents
List of Tables
List of Figures
Preface
Guidance for Identification and ^valuation
of Channel Modification Projects
Introduction
Current Governmental Involvement
Current Practices
Clearing ana Snagging
Ciiarinel Lxcavations
Cnannel Realignment
Floodways
Retarding Basins
Drainage Ditches
Sources of Pollution
Scour from Bottom and Banks
Increased Pollution from the
Use of Flood Protected and
.band
Llinination of Fish ana Wildlife
jiai->itat and Aesthetic Qualities
Types of Pollut£ints
Direct Effects
Sediment
Thermal
Page
number
Cover
I
VIII
IX
X
1
1
2
4
5
6
7
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Page
heading lumber
Movement of Pollution Uffects
Downstream m
Fish and Wildlife
Habitat Alteration 20
Indirect Lffects 21
Destruction of Aesthetics 21
Hydrology 22
Metnods of Pollutant Transport 23
Seuiment Load 23
Direct Drainage 25
Solar Padiation 26
Magnitude and Variation 28
Council on Lnvironmental
Quality Report 29
Unvironmental Assessment
Reports 29
Predication Methods 31
References 34
Additional Bibliography 34
II. Metnods, Processes and Procedures to Control
Pollution Resulting from Channel
Modification Projects 35
Design Modifications to Minimize 35
Adverse Channelization Impacts
Channel Alignment 35
Channel Capacity 37
Channel Grade 38
Spoil Placement 39
II
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Page
Heading Number
Structural Measures 41
Vegetation 44
Lffects on Ground Water 45
Structural Alternatives to In-Channel
Modifications 47
Levees 48
Floodway Channels 50
Retarding Basins 52
Land Treatment Measures to Control
Pollutant Contribution 53
Flood Proofing 54
Non-Structural Alternatives to Channelization 54
References 57
Additional Bibliography 57
III. Guidance for the Identification anu Evaluation
of Impoundments 5b
Introduction 58
Current Governmental Involvement 61
Current Practices 63
Flood Control 63
Power Production 64
iJavigation 65
VJater Supply .Storage 66
Multi-Purpose Reservoir?; 67
Sources of Pollution 68
Lasic Reservoir ilyaraulics 68
I IT
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Page
Heading dumber
Water Quality Changes wituin Reservoirs 74
Chemical-Physical Changes 74
biological Changes 77
Cite Preparation .effects on
Water Ouality 77
Releaseu Water Quality 79
Lffects on Ground Water jjo
Watershed Development 31
Ciiannel Maintenance ^3
Navigation Related Spills 34
Reduction in Waste Assimilative
Capacity a4
Types of Pollutants B6
biological Factors 37
Aesthetic Factors 90
Chemical Factors yo
Physical Factors 91
Metnods of Pollutant Transport 92
Transport into the Storage Reservoir 93
Transport within the Storage Reservoir 94
Transport out of the Storage Reservoir 95
Magnitude and Variation of Pollutant Effects 97
Water Quality Prediction Methods 9^
Empirical Techniques 9^
ilydraulic Models 99
IV
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Page
Heading Number
Mathematical Models 100
Water Quality Surveys 102
References 103
Additional Bibliography 104
IV. Metnods, Processes and Procedures to Control
Pollution Resulting from the Impoundment
of Water 106
Site Preparation 107
Multilevel Outlets
Destratif ication and hypolimnetic
Aeration 109
Aeration of Reservoir Releases 112
Control of Biological Nusisance Organisms 115
Control of Adverse Effects on Ground Water 125
References 127
Additional Bibliography 128
V. Guiuance for the Identification and Evaluation
of the effects of Urbanization 129
Introduction 129
Sources of Pollution 130
Vypes of Pollutants 135
Metnods of Pollutant Transport 137
Magnitude and Variation 138
Prediction Metaods 140
Liiiliography
V
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Page
heading Ilunber
VI. Processes, Procedures and Metaods
to Control Pollution Resulting
frora Urbanisation
Regulation of Land Use
Waste Management and Environmental
Sanitation 146
Public Education 147
Reduction of Downstream or Down-
Gradient Effects
References
VII. Guidance for the Identification and Evalu-
ation of the Nature and Extent of Dredging
and Dredged Material Disposal 151
Current Involvement 152
Current Practices 159
Sources and Types of Potential Pollutants 160
Effects of Dredging and Disposal Opera- j_g^
tion
Aquatic Disposal 161
Land Disposal 166
Prediction Methods 169
172
References
VIII. Methods, Processes, and Procedures to Con-
trol Pollution Resulting from Dredging
and Dredge Spoil Disposal
Treatment Before and During Dredging 174
VI
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Page
Heading Mumber
Aeration 174
Chemical Treatment 176
Disposal Treatment 176
Flocculation 176
Incineration 177
Filtration 178
Sewage Treatment Plants 179
Dredged Material Disposal Techniques 179
Open Water Disposal 180
jjanu Disposal 181
Marsalanu Disposal 183
Productive Uses of Spoil 184
Artifical Wildlife Habitat Creation 184
Land Development 185
Agricultural Land Use 186
References 188
VII
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.uIST OF J.V
No. Title Page
1. ileruicides Registereu for Use in or on
Water lid
2. ilerbicides Registered for Use at or Above
Water .Line 122
3. uerbicides Registered for Use on Mud
Bottoms After Drawdown 124
4. Summary of Urban Ground ,,'ater Pollutants 134
VIII
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LIST OF FIGURES
No. Description Page
i. One-Siueu Channelization Construction 40
2. channel Profile - built In Graue ana Bottom
Configuration 43
3. undisturbed Stream Channel and Separate Flood
Flow Channel 51
4. Taermal Stratification in Reservoir During
Summer Period 70
5. Thermal Stratification in Storage Reservoir
During Winter Period 72
6. Conceptual Mechanism of Ground Water Pollution
from Stock Pile Leaching 133
7. Corps of Engineers Dredging by District
Including Total Amount and Spoil Classification -,^g
Ji. Corps of Engineers Dredging by District Including
Total Amount of Metnod of Disposal
157
y. Corps of Engineers Dredging by District
Differentiating between Polluted and Non-
Polluted Spoil
IX
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Preface
Tnis report will present information including guidance
for identifying and evaluating non-point sources of
pollutants; and processes, procedures and methods to control
pollution resulting from changes in the movement, flow or
circulation of any navigable waters or ground waters,
including changes caused by the construction of dams,
levees, channels, or flow diversion facilities. This report
is mandated in Section 304(e) (1)&(2) part (F) of The Federal
Water Pollution Control Act Amendments of 1972, Public Law
92-500.
An examination of the U.S. Senate Committee on Public
Works Report which accompanied S. 2770 and the Report of the
Committee on Public Works of the U.S. House of
Representatives which accompanied H.R. 11896 was made to
guide the report preparation. This legislative history was
used in conjunction with the specific language contained in
the law. (Public Law 92-500).
The type of informational guidance and procedures
intended by the Senate Committee are described as "...the
impact on water quality of hydrographic modification
work,..." (p.49). The term water quality is defined by the
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Senate Committee are described as "...the impact or. wat^r
quality of hydrographic modification work,..." (p.49). The
term water quality is defined by the Committee as "...to
refer to the biological, chemical and physical parameter? of
aquatic ecosystems, and is intended to include reference to
key species, natural temperature and current flow
patterns...", (p.51). Thus, changes in flow patterns
through channel modification, reservoir construction and
other projects must be identified and if possible, methods
to reverse or alleviate damages described.
The descriptions in the House of Representative?
Committee Report were not as extensive as the Senate
Committee's discussion for this saction. The repcr*- directs
the Administrator to be "...diligent in gathering and
distribution of the guidelines for the identification ar.c
the information or processes, procedures, and methods for
control of pollution from such non-point sources a?...
natural and manmade changes in the normal flow of surfaca
and ground waters."
The pertinent part of the Act rf-:ads as follows: Sec
304(e)
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"The Administrator...shall issue...within one
yfcar...information including (1) guidelines for
identifying and evaluating the nature and extort of
non-point sources of pollutants, and (2) processes,
procedures, and methods to control pollution resulting
from...(F) changes in the movement, flow or circulation
of any navigable waters or ground waters, including
changes caused by the construction of dams, lavees,
channels, causeways, or flow diversion facilities."
Part (1) requires development of informational
guidelines for the identification and evaluation of
pollution effects. Such an evaluation does not require EPA
to identify and evaluate but only to provide guidance for
such. Part (2) requires identification of available
processes, procedures and methods for relieving or
ameliorating the pollution resulting from changes in flow
induced by stream nydrographic modification. The Act does
not require the EPA to evaluate such methods, but only to
identify those potentially applicable to control pollution
from such hydrographic modification.
In the process of developing this report, po^ntial
problems are identified for each hydrographic modification
technique which may not be applicable to many areas of the
All
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country or which may occur only infrequently. In
comprehensively evaluating the pollution effects o^ a
project, many factors must be considered that investigation
ultimately determines do not affect the environment.
Tnerefore, only a few of all possible detrimental factors
may need mitigation for any specific project.
Section 304 (e) of Public Law 92-500 also requires the
publication of additional material for the control of
pollution from hydrographic modification from tine to tine
after the initial report is published. For sone areas which
are not addressed by this report or for which additional
coverage is necessary, supplementary renorts will be issued.
XIII
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I. Guidance for the Identification
and Evaluation of Channel Modification
Projects
Introduction
The definition and purpose of channelization projects
are to increase the flood flow conveyance capacity of water
courses through rural or urban flood prone areas, or to
facilitate the drainage of what may be considered excessive
surface and ground water from lands which can be used as
other than natural wetlands.
This discussion will be limited to aspect? of
channelization where actual in-channel modifics4'?.on? occur.
Consideration of other aspects of channelization will be
covered under separate headings such as reservoirs.
The type of channel envisaged in this discussion is the
small stream wnich frequently floods either urban or rural
areas causing significant damage. In general such streams
would be too small for commercial navigation purnos^s but
would i>c of recreational benefit for canoeing and oth^r
activities. Also included are those drainage projects used
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to render low-lying lands usable for agriculture or
construction of suburban developments.
Current Governmental involvement
Various governmental agencies, private groups and
individuals are involved in designing and constructing
channelization projects.
The Federal agencies principally concerned with
channelization projects on a whole basin scale or mpjor
portions of basins are the Soil Conservation Service of the
Department of Agriculture, U.S. Army Corps of Engineers of
the Defense Department, the Bureau of Reclamation of the
interior Department and the Tennessee Valley Authority.
Other agencies that may be involved on a smaller scale
include the Federal Housing Administration in the Department
of housing and Urban Development, Veterans Administration
and Feueral Hignway Administration of the Department of
Transportation.
Contacts with the major Federal construction agencies
should yield listings of projects completed, under planning
and/or design and those bt-ing requested by various local
governments or private interest groups. Such contacts
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should provide information about the. major projects in a
given State or planning area.
State anu local agencies involved in channelizatior
projects are more difficult to identify in this typp of
report because of the various names such organizations uso
from State to State and locality to locality. Oft^n these
agencies will be identified in project reports prepared by
the Federal agencies as participants in a giver, project.
Organization names frequently used include a State Soil and
Water Conservation Committee, Soil Conservation District,
Drainage District, Watershea District, Conservancy District,
Flood Control District or Irrigation District. These
organizations provide local support and frequently parti?!
funding of projects constructed under the auspices of a
Federal program.
State and local governments frequently arp directly
involved in the financing of projects either on a partial
basis conjunctively with Feueral Agencies or in totality for
Federally ineligible projects.
Privately constructed projects are even more difficult
to identify. Usually, these projects are small and limited
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to one individual's or at most a fow individual'? property
These projects would generally be for drainage purposes tc
make land usable for agriculture or housing development.
Uowever, the. effects of such projects may cause significant
water quantity and quality changes in a given ar.na. These
projects may be located by examination of Department of
Agriculture aerial photographs, examination of construction
permits, inspection of recently constructed housing
subdivisions or by contact with large housing or haavy
equipment contractors in a local area.
Current Practices
Current practices can generally be subdivided into
those principally flood control oriented or tho?s
principally drainage oriented. In combined projects, design
is frequently dictated by flood control rpquirpments.
Several alternatives are generally available to accomplish
the goals of a given project. Current practice is generally
to use the method with the least cost to obtain the design
objective unless some compelling reason overrides the
economic justification.
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CLEARING AND SNAGGING
Clearing and snagging operation? may be used as ar.
independent technique for increasing channel hydraulic
capacity or it may in essence be a maintenance technique for
maintaining a previously improved channel. The basic
operation is the removal of obstructions from the channel
which impede flow directly, which increase hydraulic
friction, or which present obstructions that accumulate
debris carried by the stream during high water conditions
and thereby reduce the available area of flow.
Clearing and snagging operations are frequently used
following high water to remove accumulated debris, logs,
rocks, etc. and restore the hydraulic capacity of the
channel. Equipment used consists of bulldozers, front
loaders, cranes, draglines, clamshells, chain saws, and
winches to physically remove the obstructions.
Although less expensive than channel resactioning for
increasing the hydraulic capacity, clearing and snagging is
also less effective. For restoring hydraulic capacity in a
channel it may be the most efficient technique. However,
improvements may be short lived. In certain types of basins
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channel obstructions can re-occur within relatively short
spans of time.
ChANNEL EXCAVATIONS
Channel excavating is principally of two types. In
many cases the existing channel is enlarged and r^sheprd to
increase hydraulic capacity. In other cases the existing
channel is abandoned and a new channel is excavetpd. New
channel construction has frequently been us&d for irrigation
canals where no previous channel existed.
The design configuration and construction of tne
channel excavations depends on the purpose and physical
setting of the new channel. In urban areas whara land
values are high and flood damage losses high, channels ara
frequently designed with a rectangular configuration to
minimize land requirements and are concrete, lined to achieve
maximum hydraulic efficiency. In rural settings channels
may be designed wider with a trapezoidal shape. Siae slop&s
are determined by soil stability or by the final covering
used such as grass, rip-rap or other channel liners. In
situations where channel resectioning has resulted in
excessively steep hydraulic slopes that cause excessively
high water velocities which erode the channel bottom or side
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slopes, grade control structures are used at frequent points
along the channel to dissipate energy. An erosion resistant
lining such as concrete or rip-rap may also be used.
The technique selected for excavation varies with the
project size, whether "wet" or "dry" construction is
possible, and the method of disposing of the spoil. In
"dry" construction situations conventional drag lines,, pov/er
shovels, clam shells or front end loaders are used; in "wet"
construction situations sone method of dredging is usually
employed. The dredging method used depends on the material
to be dredgea.
CiiANWUL RUALIGNMENT
The purposes of cnannel realignment are principallv to
increase the hydraulic conductance when sufficient capacity
is unavailable frori the natural configuration and to
eliminate the meandering of the stream over the flood plain.
Without proper design, meanders frequently result in
instabilities which cause changes in the channel section and
which result in poor hydraulic efficiency. By realigninrr
the channel into a straighter and therefore shorter length,
costs of a channel improvement may be reduced when compared
with resectioning the existing channel.
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Physical constraints on realignment are existing roads
and bridges and the existence of available land for right of
way. Other constraints include costs, stability and
environmental damage. Channel realignment is complicated by
the problem of excavated materiel disposal and the
destruction of the fish and wildlife habitat available in
the old cnannel. Frequently, these "oxbows" are
intentionally maintained with sufficient flow or backwater
to maintain the habitat.
FLOODWAYS
Floodways are flow areas which are constructed to
convey floodwaters around a protected area. These flow
areas may be formed by protective dikes or be a separata
cnannel. Floodways are constructed in lieu of modification
to the existing channel or in conjunction with channel
Hydraulic improvements.
Sucn channels are designed to be dry until the water
stage in the stream reaches a predetermined flood lavel and
then to convey (in conjunction with the existing channel)
flows greater than this amount. When flood flows recede,
water is diverted from the floodwsy back into the principal
channel.
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Floodways that cut-off meanders are shorter than the
natural channel and have greater hydraulic efficiency.
Flooa stages up-and-downstream may be affected by the use of
such supplemental channels.
Since floodways are dry during normal stream flows,
they may be used for other purposes such as pasture or as
parkland. Maintenance is required to remove new growths of
trees and urush and to maintain grass cover to minimize
erosion during flood periods.
A flood control project using floodway channels
requires more land than a channel resectioning project
uecause of the dual channels and is therefore more
expensive. Maintenance costs also can be high. Maintenance
cost include removal of regrowth in the floodway and if non-
perrnanent overflow devices are used, replacement of these
periodically.
Tiie principal benefits as related to water quality are
the preservation of the natural fish and wildlife habitat in
tne natural cnannel and the maintenance of the natural
appearance of the stream.
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RETARDING BASINS
A retarding basin consists of a dam with an unget-ed
outlet. The discharge of water from the dam is related to
the height of water stored in the reservoir.
The purpose of these structures is the temporary
storage of storm water. The stored water is gradually
released when the channel capacity exists to pass thfe flow.
The stream hydrograph reflects a reduced stage of increased
duration. Flooding downstream is consequently reduced.
Consideration of such structures as par*- of a project
is influenced by actual construction costs, land acquisition
costs and the existence of acceptable terrain. The use of
these basins rather than channel resectioning is preferred
and incorporated in basin drainage plans whan feasible.
DRAINAGE DITCHES
Drainage ditches are included in channelization project
planning but seldom dictate the design channel capacity.
Channel capacity normally is controlled by flood flow
conditions. Drainage ditch projects usually involve
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deepening previously constructed ditches or in constructing
new ditches.
Where ditches are used to lower the water table and
enhance drainage/ the dry weather stream flow? may be
reduced in the main channel if the ditching project, cover? a
sufficiently extensive area. Some increase in main channel
peak flows may occur because of better interception of
surface run-off and the more efficient hydraulic conveyance
of sucn run-off than previously existed.
The depletion of ground waters and subsequent re-auction
of stream flows can impair quality in both surface a"u
subsurface waters. In addition to the reduction of fish and
wildife habitat, there is a decrease in dilution watpr for
organic materials and a modified seasonal water temperature
pattern. Ground water infiltration tends to incr-cps*1 stream
temperatures during the winter season and dscreas-1 stream
temperatures during the summer-season.
Sources of Pollution
Following the initial vegetative recovery aft«r the
various cuannel modifications are constructed, both direct
and indirect sources of pollution are identifiable.
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Realizing that the main purpose of channelization project?
is either to increase hydraulic capacity to convey flood
waters thus protecting adjacent property; or to provide
drainage of land to increase its economic usefulness, the-
effects in terras of environmental pollution are apparent.
SCOUR FROM BOTTOM AND BANKS
In order to enhance the hydraulic efficiency of
channels by resectioning, realignment, or even clearing ar*d
snagging, the channel roughness is reduced. Such a
reduction in roughness decreases friction losses and thereby
increases the velocity of flow. If the channel is not
properly designed, the* increased flow velocities may exceed
the stability velocities of the bottom or bank materials and
cause erosion or scour. This in turn degrades the, channel
and furnishes sediment for stream transport, destroys
natural habitats and detracts from the aesthetic? of tne
stream.
Perhaps the worst offender in this regard is channel
straightening and realignment. This process reduce-.? channel
lengths but not the decrease in elevation over which the
water is lowered in traversing a stream section. The net
result is a substantial increase in the stream gradient with
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resulting substantial increases in stream velocities.
Without extensive control measures for stabilization aid the
use of grade control structures, channel degradation car be
extensive.
INCREASED POLLUTION FROM THE USE OF FLOOD PROTECTED AND
DRAINED LAND
Following the implementation of both flood control a^d
drainage projects, extensive amount? of land becom»
available for higher economic production. Land formerly
used for pasture or low return agricultural crops can be
converted to high yield agricultural crops. Within
municipal areas, property value? are incraasad aid use 9 with
more economic return can be developed. With the increpsi-.a
land use there is potentially environmental degradation.
Enhanced agricultural use is accompanied by incr^
fertilizer, herbicide and pesticide use and by increased
land tillage which may increase the erosional soil loss.
The by-products of this agricultural use drains to the
stream and causes various amounts ana kinds of water quality
impairment. The kind and amount of such pollutant? enterirg
the stream would be determined by the. soil type, land slop."
and cropping practice.
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Channelization projects which provide flood protection
within urban areas frequently include the provision of lined
channels. The effects on the water environment of these
channels are both the destruction of fish and wildlife
naoitat and the destruction of aesthetic qualities.
ELIMINATION OF FISH AND WILDLIFE HABITAT AND AESTHETIC
QUALITIES
The various channelization practices have varyinq
effects on fish and wildlife habitats. In general, the more
extensive the modification structurally the more damage is
caused to habitat areas. For example, concrete lining of
channels eliminates habitat areas for practical purposes
whereas at the other extreme, clearing and snagging may not
nave a detectable effect. The effects of the project can
only be determined by the use of before and after surveys
designed to detect both drastic and subtle changes.
Aesthetic values for streams depend a great deal on the
beholder. Swamp habitats may be quite disagreeable to a non-
naturalist whereas parkland or pasture beside an improved
channel may appear quite pleasing. To this extent
aesthetics may be an acquired attribute in conjunction with
strictly innate appreciation. Aesthetics is the most
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difficult environmental factor to quantify and it nay
require the opinion of a representative cross section of the
population before classification of a project as
aesthetically acceptable.
Types of Pollutants
This uiscussion will be limited to the common
pollutants both contributed directly and indirectly. Such
pollutants are the common denominators to be anticipated
from the majority of projects.
DIRECT EFFECTS
Sediment
Seuiment is perhaps the most ubiquitous of all
pollutants associated with channelization. The most
pronounced effect on sediment occurrence and concentration
is during the construction phase of the project. With bare
soil banks and a non-stabilized channel, the natural stream
flow itself and any rain that occurs flushes sediment into
the streau discoloring the water and makinq it turbid.
Following stabilization nowever, the stream frerruently
remains more turbid than before the project v;as constructed.
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Every stream has an ability to naturally transport
certain amounts of sediment. The amount transported is
termed sediment load and is a definable stream
characteristic. When channel hydraulic characteristics are
changed by constraining the channel to a fixed location, by
realignment, or by other means, the velocity of water flow
is changed and consequently the ability to transmit sedinent
is likewise changed.
The effects of increased sediment on water quality are
to reduce light penetration, to periodically blanket fish
spawning areas, to periodically blanket and suffocate
aquatic insect larvae used by fish as food, to create
shoaling and instabilities in the channel itself, and to
cause problems with sedimentation in unimproved channel
sections downstream from the project section. In addition
to these problems which directly affect instream water
quality, increased costs are realized by water users
including water suppliers and irrigators. Additionally,
aesthetic quality is reduced to a substantial degree. ,
Thermal
The design of channelization projects for flood
prevention requires increased channel dimensions. Because
If,
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of the enlarged channels, the dry weather flow is directed
near the center of the channel. The strean flow is thus
deprived of shade provided by trees along the banks and is
exposed to solar radiation which heats the water.
Previously in the natural channel, the presence of such
trees along the banks provided shade for the flowing water
and helped moderate stream temperatures.
In addition to reducing temperatures during daylight
nours, the insulating effect of these trees is removed and
night tine tenperatures are reduced to a greater extent than
previously. Thus, a greater diurnal variation in
temperature can result from a channelization project.
The temperature effects on fish and other aquatic life
are caused Dy both the absolute temperature itself and the
temperature variation. Both increased maximum temneratures
and increased variation can have detrimental effects on fish
and other aquatic life during various stages of their life
cycle. Specie selection, availability of food, attendant
life cycle chemistry and water quality changes are all
phenor.iena that are temperature affected.
Water quality is directly affected by increased
temperature. Dissolved oxygen is removed more rapidly by
17
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temperature, uissolved oxygen is removed more rapidly by
temperature-mediated bacterial oxidation of soluble and
suspended organic materials. This problem is compounded by
the reduced solubility of oxygen at higher temperatures so
that a resulting decline in stream dissolved oxygen
concentrations results. Decreased dissolved oxygen
concentrations stress aquatic life dependent on this
constituent.
Movement of Pollution Effects Downstream
In channel relocation or realignment projects where
channel lengths are substantially reduced, the effect of
increased water velocity can be pronounced. One effect of
increased velocities on surface water quality is to increase
the length of stream affected by pollutants whose effects
are time dependent. The organic materials in discharged
wastes and the drainage of natural organics from swampy
areas along the stream are bacterially degraded and oxidized
in the course of moving downstream. With an increased water
velocity these materials move much farther in distance for
the equivalent period of time required for completion of the
biochemical reactions. Thus the effects of reduced
dissolved oxygen levels extends farther downstream than
previously.
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In the case of dissolved oxygen the effect of extending
the reaction over a greater channel length nay be
beneficial. The increased water velocity also increases
reaeration which counteracts the decrease in dissolved
oxygen concentrations caused by biochemical oxidation
reactions. This effect may be sufficient to prevent
dissolved oxygen concentrations fron decreasing to previous
low levels and thereby enhance water quality.
In contrast, the effects on feces-associated bacterial
levels downstream from a discharge would be to expand the
distance over which a health hazard would exist. The die-
away reaction for these bacteria is also tine related. The
extension of such a health hazard is detrimental to water
quality.
Increased water velocities also are capable of
transporting increased sediment loads which may be deposited
in non-channelized areas downstream. The phenomenon of
sediment deposition tends to migrate upstream clogging
channels and defeating the channelization improvement unless
removed during maintenance operations.
In addition to simply transporting more sediment,
increased velocities will, if large enough, make streams
19
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more aggressive in eroding channels and stream banks which
destroys much of the usefulness of the stream for other
purposes.
Fish and Wildlife Habitat Alteration
Almost any modification of a channel alters the
existing habitat for fish and wildlife. Not all such
changes are detrimental however, provision of water storage
for example may provide increased habitat areas but perhaps
for a different than pre-project biological assemblage.
Most in-channel modifications do remove obstructions
that are used by fish for protection from predators, for
fish food habitats and for backwater breeding areas.
Removal of trees and brush along stream banks removes
protective cover ana food sources for various water-related
wildlife.
Many of these effects can be mitigated by incorporating
proper factors into project design. For example,
maintenance of water in cut-off oxbows helps retain
available fish and wildlife habitats.
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INDIRECT LFFECTS
Destruction of Aesthetics
Channelization projects have frequently been criticized
for the destruction of aesthetic values of natural streams.
The creation of geometrical shaped channels with highway-
type alignment is not conducive to aesthetic appreciation by
naturalists or the general public. It is possible to
mitigate uuch of the aesthetic destruction by use of proper
design techniques. For example, those techniques which only
alter one stream bank or which provide a replanting proaram
to establish vegetation similar to that existing prior to
construction can be used. Other similar measures can be
included to minimize the reduction of aesthetic values.
It should be mentioned also that aesthetic values can
DC enhanced for many people by various channelization-
related projects. In many instances public accessibility to
water courses is improved and parks or other recreation
facilities can be incorporated into the right-of-wav
acquired for the project.
In-stream techniques can also be applied to maintain
fish and wildlife habitat. Construction of pool and riffle
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areas is one technique available. Use of more natural
alignment and other design features are available to project
planners.
Hany of the effects on basin hydrology of a
channelization project can be anticipated. The major effect
is to increase the hydraulic capacity of the principal
channel and the smaller channels which urain into the
principal channel. The principal effect of this change is
to move water more rapidly through the channel. Downstream
from the cuannelization project these increased flox^s may
cause increased flooding by shortening the time of
concentration of peak runoff following heavy rains.
Drainage projects may aggravate this problem by
allowing higher valued operations on the drained land. If
the higher valueu use is urbanization, then the paved areas,
including roof areas, drain water to storn drains which
convey water to the water course even more quickly than
previously occurred and increase peak flow rates and
subsequent flooding.
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Drainage facilities also tend to lower the water table
during wet periods of the year and deprive streans of the
critical base flow required during dry weather periods of
the year.
Methods of Pollutant Transport
The methods of pollutant transport in channelized
stream basins are essentially the same as in the unaltered
stream basin. Certain transport mechanisms are either
increased or decreased by the effects of the alteration.
SliUIMliWT LOAD
As indicated previously, sediment load is the amount of
sediment characteristically carried by a particular water
course. It consists of suspended and bedload sediments.
Beaload sediment is sediment that is transported in a stream
by rolling, sliding, or skipping along the bed very close to
it; that is, within the bed layer. Sediment load is related
to several factors but principally the hydraulic
characteristics of the stream and the soil and geologic
characteristics of the stream channel and drainage basin.
23
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The effects of a channelization project is generally to
cause an increased amount of sediment load. Improved
Hydraulic conveyance produces increased water velocities
whicii in turn increase sediment transport capability. If
the strearobed is improperly stabilized following
construction, this increased sediment load can be dramatic.
Liven though proper stabilization techniques are used,
concentrations of sediment generally increase excent in the
special case of complete channel lining with concrete or
other paving materials. Downstream from the channelization
section, these materials can settle and fill the channel
with excess sediment destroying hydraulic efficiency and
stream biology and increasing the potential for stream
meander formation.
Indirect effects of channelization are to enhance land
for iiigher economic uses such as increased agricultural
production or urban and commercial development. Many of the
pollutants generated by these new uses become adsorbed with
soil grains. Such organics as pesticides are particularly
susceptible to such adsorption. When these soil particles
are flushed into the stream, the adsorbed materials are
likewise carried along for later deposition downstream.
Following such deposition, these materials can enter the
life cycle of the stream. Biological concentration in the
24
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aquatic food chain may cause significant ecological
disturbances.
Tiie increased sedinent load can be visible as increased
turbidity of the stream water. The principal effect is to
decrease the aesthetic value of a stream. On larger streams
used for water supply purposes, increased turbidity causes
increased treatment costs for potable or industrial water
users.
Excess channel scour can cause increased sediment loads
and downstream deposition, adsorbed pollutant transport, and
direct detrimental effects to water suppliers and stream
aesthetic values.
DIRECT DRAINAGE
The increased uses of land adjacent to streams
following the provision of flood protection and drainea
arable land provide sources of pollution which directly
drain into the water course. Many of the pollutants cirise
as the normal product of urbanization or farming practices.
Others arise because of the removal of natural mechanisms
which trap contaminants directly or provide detention time
for the adverse effects to decay to acceptable levels.,
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With tine, many pollutants are degraded into innocuous
substances. Nature provides detention tine in natural
oackwaters and in sluggish neanderinq streams. Pollutants
in solid form or which naturally flocculate and settle are
assimilated and may be destroyed in the bottom sediments by
microbiological activity. Phosphorus is chemically removed
as an insoluble salt while nitrogen and sulfur compounds are
removed by conversion to gaseous forms which evolve to the
atmosphere. Following channelization and drainage projects
these natural places of detention are by-passed or removed
which has the effect of increasing pollutant concentrations
in the flowing waters. The effects of these pollutants are
then transferred downstream decreasing water quality while
in passage.
SOLAR RADIATION
Tne light provided by the sun provides the energy for
the biology of natural waters. The so-called "food web"
begins with primary production by algae which are capable of
photosynthetic production and continues up through the
consumer species including aquatic insects and fish. Too
little solar radiation produces too few algae, little
primary production, and sparse fishery. Too much sunlight
heats the water, provides a competitive advantage for
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undesirable biological species arid an unsatisfactory
fishery. The effects of solar radiation are both on the
water quality itself and on the biological response and
effects to that water quality.
In many streams light penetration extends essentially
to the stream bottom ana provides energy for attached algae
which provide both food and oxygen for aninal life. In
streams characterized by alternating pool and riffle areas,
these productive areas are near the edge of the strean
extending toward deeper water until the incident light is
extinguished to less than photosynthetically usable levels.
Following channelization, the stream channels are frequently
made deeper reducing light penetration from forner levels.
Thus the habitat is altered and a different biological
assemblage develops. Frequently, the new assenblage is
composed of less desirable species.
Thermal effects become evident when shade trees and
brusii are removed allowing both more tine and increased
surface area of exposure to sunlight. Coldwater snecies of
fish can not tolerate the elevated water temperatures cind
are replaced Dy warm water species. The direct effect of
increased solar radiation may indirectly change the stream
fishery.
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Magnitude jind _ Var iat icm
Available statistics for defining the national
magnitude and variation of channelization projects indicates
that perhaps 200,000 miles of waterways have been altered in
the last 150 years in the United States. Since the
initiation of Federal projects in the early 1940's planning
for and development of about 34,240 miles of waterways in
1,630 projects have been initiated under the Federally-
assisted local protection and small project programs of the
U.S. Army Corps of Engineers and watershed programs of the
Soil Conservation Service. Additional projects have been
initiated by the Bureau of Reclamation, the Tennessee Valley
Authority and other Federal, State and local agencies.
The Corps of Engineers have assisted in 889 projects of
which 47 percent involve channelization and 53 percent
involve levees. Of these projects 6,180 miles (56%) are
completed, 3,896 miles (35%) are under construction and
1,001 miles (9%) are planned. The median size for these
projects is about 4 miles with two thirds under 5 miles and
80 percent less than 10 miles.
Tne Soil Conservation Service assisted in 558 projects
of which virtually all involved channelization. Of these
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projects 4,209 miles (25%) were completed by 1971 and 12,426
miles (75%) still remaining to be completed. The median
size of the projects is about 18 miles with 38.7 percent
less than 10 miles and 24 percent less than 5 miles.
COUNCIL ON ENVIRONMENTAL QUALITY REPORT
The Council on Environmental Quality's report (Ref. 1)
discusses 42 different projects of 4 different Federal
agencies. Each project was analyzed among other things for
the basis of project formulation, physical effects of the
completed project and the biological effects on the aquatic
and terrestrial systems. The methodology used in preparing
this report is an excellent guide for those evaluating
additional projects.
ENVIRONMENTAL ASSESSMENT REPORTS
Since the enactment of the National Environmental
Policy Act of 1969 (Public Law 91-190) each Federal agency
participating in a proposed channelization project that
significantly affects the quality of the human environment
must prepare an environmental impact statement. These
statements must assess the following for the project:
(Title 42 U.S.C., Sec. 4332)
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"(i) the environmental impact of the proposed
action
(ii) any adverse environmental effects which
cannot be avoided should the proposal be
implemented
(iii) alternatives to the proposed action
(iv) the relationship between local short-term
uses of man's environment and the maintenance
and enhancement of long term productivity,
and
(v) any irreversible and irretrievable
commitments of resources which would be
involved in the proposed action should it be
implemented."
In accordance with NLiPA all proposed projects
significantly affecting the environment have such renorts
prepared. These reports are made available for review and
comment in draft form. Final reports incorporating comments
of reviewers are submitted to CEQ and are available unon
request from the preparing Federal agency.
30
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The environmental effects of a project are
comprehensively covered in these reports. Whether or not
the agency is able to mitigate the adverse effects
identified in the environnental assessment, discussion o^
these effects is included. For most projects these
assessments are invaluable in evaluating a project.
It should also be pointed out that several States have
also enacted statutes patterned after NEPA which reauire an
environmental impact statement before the expenditure of
State funds or in some cases before permits are issued to
private interests for project construction.
Prediction Methods
Methods to predict the effects of channelization
projects will not be directly presented in this report. A
tremendous volume of literature exists discussing the
effects on water quality caused by various phvsical
modifications of streams. Several sources of information
will be mentioned as convenient and comprehensive starting
places for project evaluation including the mitigation as
much as possible of the inevitable adverse effects.
31
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The CLQ report on channel modification (Ref. 1)
presents the results of extensive biological investigations
conducted by the Philadelphia Academy of Natural Sciences.
Chapter 5 of Volume I of this report entitled, "Effects of
Channel Modifications on Fish and Wildlife Resources,
ilabitat, Species Diversity, and Productivity" directly
addresses the biological effects observed in 21
channelization projects analyzed. The same or similar
effects therefore are to be anticipated in other projects
under comparable conditions. Discussion includes the
effects of channelization projects which cause erosion,
consequent sediment accumulations and unstable stream beds,
remove solid substrates, or decrease light penetration which
may affect the biological population by disturbing the
number of species, the populations of each, or the
productivity of the stream, and alternatives to channel
construction which will avoid adverse effects altogether.
Methods to predict the effects of channelization
projects are included in a volume produced by the Soil
Conservation Service entitled, "Planning and Design of Open
Channels" (Ref. 2). This document comprehensively presents
available information on channel design including the
estimation of anticipated flows; location, alignment and
hydraulic design; and channel stability design. A recently
32
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auded chapter 7 (1971) includes environnental
considerations. The tecnnical methodoloqy presented in this
document is sufficient to predict the effects of the
nydraulic changes caused by a channelization project
including any increases in sediment transport.
Increases in the stream temperature and the diurnal
variation are not so readily predicted. These calculations
can only be made by estimating the amount of protective
shade removed, changes in depth and changes in channel
length in conjunction with tables of solar radiation values.
Such calculations will probably only yield approximate seni-
quantitative amounts of change.
The best technique for evaluating potential effects of
channelization on a stream is the field survey of a nearby
stream which has undergone the changes projected for the
stream of interest. Comparison of this type of information
establishes a more rational basis for predicting the various
physical, chemical and biological changes to be anticipated.
In the absence of such a situation, predictive techniques
from the sources suggested above and in the companion report
entitled, "Methods, Processes and Procedures to Control
Pollution Resulting from Channel Modification Projects" are
available for use.
33
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References
A. D. Little, Inc., "Report on Channel Modifications,"
submitted to the Council on Environmental Quality, U.S.
Government Printing Office, Washington, D.C. ("'arch,
1973).
Anon., "Planning and Design of Open Channels,"
Technical Release Jo. 25, U.S. Department of
Agriculture, Soil Conservation Service (December, 1964,
Revi s ed March , 1973).
Additional Hibliography
Anon., iJational Lug i nee ring Handbook , Section 16,
Drainage, Chapter 6. Open Ditches for Agricultural
Drainage, U.S. Department of /agriculture, Soil
Conservation Service (February, 1959) .
Todu, D.iv.., Ground Water hyurology , John Wiley & Sons,
Inc., u'ew York "
Anon., Wator_ Quality Criteria , Report of the National
Technical .Advisory Committee to the Secretary of the
Interior, Section 1, Recreation and Aesthetics, Federal
Water Pollution Control Adninistration (April, 196b) .
Dewiest, R.J.I1. , "Replenishment of Aquifers Intersected
by Streams, Jour, of the hydraulics Division, A.S.C.E.,
Uo. uY6, (November, 1963) .
Anon., "Sedimentation Transportation Mechanics: G.
Fundamentals of Sediment Transportation," A.S.C.L.
Task Committee on Preparation of Sedimentation Manual,
Committee on Sedimentation, Journal of the hydraulics
Division, A.S.C.L., Uo . HY12 (December, 11)71).
Ilackentnun, K.M., The_ Practice of_ Water Pollution
Biology, U.S. Department of tha InteriorT Feueral Water
Pollution Control Auministration (1969) .
34
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II. Methous, Processes and Procedures to Control Pollution
Resulting fron Channel Modification Projects
This discussion will be limited to those design chancres
in the actual channel modification project that can be
incorporated to enhance and mitigate undesirable by-
products. A brief discussion will be directed to
consideration of alternatives to channel modification such
as flood plain zoning regulations. Discussion of other
structural alternatives including upstrean storage
reservoirs are covered under separate headings.
Jesign Modifications to Minimize Adverse Channelization
Impacts
Channel improvement projects generally are designed to
follow existing stream alignment with tae exception of
situations where stability or cost factors force an
alternative course. Also, changes are often made to provide
larger parcels of flood free land. In stream sections
passing through highly erodable soils for example, an
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alternative course may be desirable if an alignment through
more stable soils exists. Relocation may also be desirable
to avoid passage through otherwise valuable lowland areas
which serve as fish and wildlife habitats.
In the design for channel construction the alignment
generally should follow a natural pattern which should
consider the type of existing stream, the required hydraulic
capacity and comparison with upstream and downstream
sections of the particular water course or a similar nearby
water course. The use of such design techniques avoids the
unnatural appearance of a modified channel thus improving
aesthetic appeal. In many cases such design may aid channel
stability by not changing the channel gradient excessively.
Special features along the stream should be protected
to enhance aesthetic appeal. By proper design of channel
alignment the existence of particularly striking features
can be preserved and perhaps enhanced which adds to the
public appreciation of the projects. Design should
incorporate provisions to protect these features including
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special stream and streambank stabilizing measures, land
treatment methods and grade adjustments.
CHANNEL CAPACITY
Cnannelized streams should convey water discharges
ranging from base flow to the design flood flow without
damage to the channel itself. The low flow channel cross
section should approach the natural stream condition. The
bottom width ana side slopes can be designed to simulate the
natural channel so that it will blend with upstream and
downstream sections of the natural channel and avoid a
monotonous appearance. At bends, the channel side slope can
be steepened on the outside of the channel bend and
flattened on the inside to simulate natural waterways. Use
of naturally occurring rocks and boulders can be placed at
selected points for aesthetic appeal, energy dissipation and
fish-nabitat development. The botton width of the channel
can be varied in conjunction with the channel slope to
develop pool and riffle areas to aid fish and wildlife yet
maintain hydraulic capacity. The use of rip-ran made fron
native rock improves the aesthetics, offers hiding places
for crustaceans, small fish and other aquatic biota, and
gives the banks and channel bottom stability in an otherwise
erosive channel. Inclusion of these devices however
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requires the careful attention of the designer, the on-site
inspection personnel and especially the contractor.
GRADE
Within the topographic constraints of a given project,
the channel gradient can be varied between strean reaches to
achieve naturally appearing pool and riffle areas, cascades
or other such features. To accommodate the existence of
highly erosive soils in certain reaches, gradients can be
flattened. Conversely, in erosion resistant soils gradients
can be steepened. All such changes must remain within the
natural topographic constraints of channel elevations at the
beginning and end of channel sections. The use of such
grade variations not only enhances aesthetic appeal but
increases protection against meander development, increases
channel stability and minimizes sediment from channel and
uank erosion.
Adjustment of the channel gradient to develop pool and
riffle areas can also provide increased atmospheric
reaeration capacity in the stream. Reaeration increases
with increased velocity and decreased stream denth. Riffle
areas provide additional turbulence which also tends to
increase reaeration. Vhe increased dissolved oxygen
33
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supplied by the increased reaeration improves the habitat
for fish and aquatic life. It also provides additional
capacity to satisfy the denands exerted for the oxidation of
naturally occurring or man-contributed organic material
before damage to aquatic life occurs.
SPOIL
The on-site placement of excavated spoil material
should be accomplished so as to minimize the amount of
clearing required or other land disturbing activities.
Spoil should be placed in such a fashion so as to minimize
the potential for the erosion of the material back into the
stream. Placement of spoil should also be made so as to
minimize the adverse effects on wildlife habitats and may be
concentrated at selected locations along the stream section
to accomplish this goal. Through proper re-vegetation and
planning the spoil may be used to create scenic overlooks
and other contrasting features which may enhance the
aestnetic appeal of a project and avoid the monotonv of
continuous spoil banks beside the stream.
The amount of spoil can also be minimized by the \ase of
one-sidea or single stream bank construction where
appropriate (Figure 1) . Other spoil reducing measures can
39
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ue included by the use of non-structural alternatives
totally or partially in lieu of actual channel modification,
STRUCTURAL MLASUKES
Structural measures can be included in a channel
modification project to maintain stability by alleviating
problems of excessive grade. Structural measures can also
be applied to side stream entry points to control the
introduction of sediment, debris or other pollutants or
effects.
For channels with excessive slopes which would
otherwise erode anu produce sediment, typical structual
measures include drop structures, chutes, steepened rock-
armored sections and cascade structures. Uach of these
structural modifications provides resistance to high
velocity flows and allows the use of stable, moderate
gradients upstream and uownstream.
41
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For channels with sufficiently flat gradients so that
channel and bank stability are not problems, designs can be
incorporated using the pond, riffle and pool sequence. The
inclusion of ponding provides sufficient excess elevation
that succeeding pool and riffles can be maintained. Besides
protecting fish iiabitat, aesthetic appeal is increased
(Figure 2) .
Siue channel structures include pipe drops, lined
chutes anu drop spillways. These structures can be used in
conjunction with sedinent basins and debris traps to retard
the input of these materials into the main channel. The
principal purpose of these structures is to prevent the loss
of vegetation from stream banks at the point of entry,
slumping of the main channel bank or the cutting of a deeper
tributary channel. All of these effects contribute sedinent
to the main channel and reduce channel stability.
42
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VEGETATION
The early re-establishment of vegetative cover
following in-channel modifications is most important to
prevent extensive erosion and damage to the hydraulically
improved channel. The selection of the plantings should
incorporate both an initially quick growth to stabilize the
bank and the subsequent development of a cover which will
blend with or simulate the natural cover.
Use of proper erosion resistant cover will keep
sediment concentrations and adverse water quality impacts to
a minimum. Proper selection of trees and bushes will
enhance biological productivity within the stream itself and
the associated wildlife. Shade provides against excessive
solar radiation which helps maintain temperatures within
allowable tolerances and insulate against excessive diurnal
thermal variations.
Use of acquired right of way for parks, hiking paths or
the provision of access for fishing is also enhanced
aesthetically for public use by the use of suitable re-
vegetation practices.
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EFFECTS OU GROUND WATER
Any channel modification may alter the natural
circulation of the ground water. Natural recharae to the
ground water may be increased or decreased denendina upon
location, depth, ana other characteristics of the new
channel. Thorougn investigation of possible effects on both
the quantity and quality of ground water should be nade
Before undertaking a channelization project.
An important distinction in terms of their effect on
ground water quality is whether channels are lined or
unlined. A lined channel, constructed of an imnemeable
material such as concrete, may prevent the natural
interchange of streamflow with ground water. Such a linina
may be required to provide flood protection in an area with
unstable soils.
In areas where such recharge is important, water can be
artificially recharged to the ground water. This can we
uone by installation of ditches or basins for artificial
recharge in the vicinity of the lined channel. High-quality
water diverted from the stream or derived fron some otner
source ana released into these structures would infiltrate
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to tiie ground water and thus compensate for the loss of
natural streambed recharge.
In unlineci channels, a primary effect is that produced
ijy changing the water table elevation in the area adjacent
to the channel. If a channel is dredged in an area where
the water table is close to the land's surface, the new
channel acts as a drain and lowers the water table. If the
water table elevation needs to be maintained at pre-
channelization levels, the effect of lowering the level can
jje negated by lining the channel with an impermeable
material. Tnis will prevent dewatering of the upper portion
of che aquifer and hence maintain the original natural
conditions of ground water quality. Some drainage to
prevent uplift of the channel lining may be necessary.
There may be some loss of bank storage of water even
with unlined channels if the hydraulic characteristics are
improved and the gradient steepened, resulting in higher
velocities. The effects on ground water quality are the
same as for lined channels. Artificial recharge can be used
to compensate for the loss.
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Unlined channels nay allow polluted water to enter the
ground water if there is no impermeable barrier between the
bottom of the channel and the ground water body.
In some coastal areas natural channels have been
deepened or new channels excavated. These have sonetines
cut deeply into or through the underlying clay formation
which originally acted as a natural barrier and prevented
the downward movement of saline water into the underlying
freshwater aquifers. Serious ground water pollution has
resulted. Such channels should be located, designed, and
constructed with care so that the natural barriers to saline
water intrusion will not be impaired. If this is not
possible, the channels must be artificially lined.
Structural Alternatives to In-Channel Modifications
In many cases in-channel modifications can be reduced
substantially or avoided altogether by the use of various
alternative designs involving construction of off-strean
facilities. Such facilities as levees, floodways, retarding
basins, building flood proofing and land treatment can be
incorporated into projects to avoid actual channel
modification.
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LEVEES
Levees are generally low structures located along the
edges of surface water bodies such as rivers, reservoirs,
lakes, and the sea to prevent inundation of land behind the
levees during periods of high water levels resulting fron
floods, storms, or tides. Levees also may be constructed to
form a controlled channel. A floodwall serves the same
purpose as a levee but is constructed of concrete or masonry
to save on right-of-way acquisition. Only in rare instances
do levees or floodwalls extend deeply enough into the
subsurface to form a barrier to ground water flow.
In coastal areas levees prevent the flooding of land by
seawater. As a result, the quality of ground water in the
aquifers behind these levees is protected.
Occasionally a harmful effect of a levee on ground
water quality may occur in floodplain aquifers near streams.
The dissolved mineral concentration of most floodwaters is
lower than that of ground water. During periodic
inundations of floodplains, some of the water infiltrates to
the floodplain aquifer and acts to improve its quality by
dilution. Where a levee prevents this action and reduces
the natural recharge, the mineral quality of the aquifer
43
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will tend to change with time. The existence of such
localized flood plain aquifers is confined to special
geological situations and is not a common problem throughout
the country.
Tae effect on surface water quality of levees located
along a channel is principally the encouragement of erosion
and channel scour during high water periods which contribute
sediment and increase water turbidity. Since the stream is
confined by the levee to a smaller than natural flood
channel, water velocities are increased above natural
conditions causing channel scour. The increased scour can
subject underlying less resistant geological formations to
attack and perhaps even breach aquitards opening acmifers to
pollution by contaminated surface waters.
Control methods include use of wider spacing between
levees to provide additional area of flow and the use of
stabilization techniques on the levees themselves and in the
flood plain such as plantings or rip-rap. Levee maintenance
is important to continue both the protection against floods
and to reduce the production of sediment caused by erosion
and scour.
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FLOODWAY CHANNELS
Floodways are usually wide artificial channels
constructed to carry floodwaters that exceed the capacity of
natural river channels. As such, these are invariably
unlined, and the bottom elevation is at or close to the
natural ground surface level.
The effect of most such channels on ground water
quality is minimal, particularly as they typically carry
water for only a small fraction of each year. If anything,
floodwater flowing in a bypass channel and infiltrating into
the ground would tend to improve the local ground water
quality.
Because of the negligible effect in degrading ground
water quality, no specific control measures are suggested to
prevent pollution of this resource.
The effect on surface water quality depends on channel
stability measures incorporated into the design of the
floodway and the maintenance provided. Incorporation of
proper replanting and rip-rapping of channel bends prevents
the scour of sediment during high flow periods (Figure 3).
Insufficient maintenance can lead to the production of
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Excavate One Side Only
To Flood Flow Grade
oJ from Tecii. Kelc-dSu ,io. ^,
Soil Conservation Service, USUA, 1971
Spoil
UNDISTURBED STREAM CHANNEL & SEPARATE FLOOD FLOW CHANNEL
Figure 3 Undisturbed Stream Channel and Separate Flood Flow Channel
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substantial quantitities of seaiment and debris which
decreases water quality downstream.
RETARDING BASINS
These basins are constructed on tributarv streams and
in the main stream. By regulating the hydrograph
downstream, flood stages are reduced and damages due to
flooding consequently reduced.
Water quality is generally unchanged bv these basins
during low flow conditions as the water passes through
essentially without alteration or retention. During the
high runoff periods, the basins help reduce sediment
concentrations and trap debris. If accumulated sediment and
debris are not removed during maintenance operations,
sediment storage will be filled and any additional
quantities will be transported downstream.
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Proper stabilization, planting programs and the use of
sediment trap ponds help alleviate erosion and subsequent
input of sedinent directly into the basin and prevent caving
and slumping of the inundated areas durina high water.
LAu'D TREATMENT MEASURES TO CONTROL POLLUTANT CONTRIBUTION
Land treatment measures include proper land use
management techniques and the use of erosion-controlling
vegetation in the drainage basin. These measures are
effective in reducing sediment-bearing runoff and extending
the time for runoff itself during light and moderate
rainfall periods but are not particularly effective during
heavy rains that lead to flooding. Where bottomlands are
cultivated and raw crops are placed adjacent to a
channelized stream, it is frequently advisable to leave a
filter strip of grass or shrubs along the stream to renove
silt and to prevent erosion of the channel banks by field
runoff. Basically these measures are beneficial and do not
require abatement measures.
53
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FLOOD PROOFING
Flood damage can be avoided bv structural modification
of buildings in the flood plain. The modifications used
include reinforcing of foundations to resist the forces of
flood water and the tenporary weakening of supnorting soil,
sealing of windows located at lower elevations than the
expected flood water level, and providing for water-tight
closure of doors. Other neasures recommended entail the
moving of appliances, inventories and other valuable
materials to the upper stories of buildings so as to be
above expected flood water levels. Flood proofing is most
effective for new construction as the required modifications
can be expensive for older structures.
non-Structural Alternatives to Channelization
The principal purpose of channelization projects is to
reduce the damage caused by periodic floodina. Thus far in
this report, the physical methods to mitigate the water
quality degradation that occurs because of such channel
modification have been discussed. One alternative to a
physical solution to prevent damage from flooding is to
delineate areas subject to flooding and prohibit uses of
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these areas that are damaged by floods. Sucn non-structural
alternatives can eliminate the pollution effects directly
attributable to channel modification anu if proporly planned
and enforced can eliminate pollution effects that would
otherwise occur when the project uesian flood is exceeded
and flooding occurs.
The CLQ Report (Ref. 1) summarises these approaches as
follows:
"Jon-structural adjustments take many forms. The three
major measures are regulatory, technical/administrative/
policy, and economic/financial measures. Powers, programs
and incentives are available for each. Regulatorv measures
combine State encroachment statutes, local rural and urban
zoning ordinances, subdivision regulations, building and
iiousing codes, and open space regulations.
Technical/administrative/policy measures combine flood
proofing, temporary (preplanned) and permanent evacuation,
flood forecasting and warning systems, alternative uses of
protective works, lending policies, local facilities
development policies, urban renewal, and relief and
rehabilitation policies and programs. Uconomic/financial
measures combine flood-risk insurance, tax adjustments,
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tax adjustments, rights, easements, dedications,
reservations and public or private acquisitions."
In practice, a combination of the structural and non-
structural approach is taken to reduce flood damage. For
any given situation, the effects of the alternatives on
water quality should be calculated and considered in the
overall project evaluation.
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References
1. A.D. Little, Inc., "Report on Channel Modifications,"
submitted to the Council on Environmental Quality, U.
Government Printing Office, Washington, D.C. (March,
1973).
2. Anon., "Planning and Design of Open Channels,"
Technical Release No. 25, Chapter 7, Environmental
Considerations in Channel Design, Installation and
Maintenance, U.S. Department of Agriculture, Soil
Conservation Service (October, 1971).
Additional Bibliography
1. Anon., Water Quality Criteria, Report of the National
Technical Advisory Committee to the Secretary of the
Interior, Federal Water Pollution Control
Administration (April, 1968).
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III. Guidance for the Identification and
Evaluation of Impoundments
Introduction
This discussion of impoundments will describe the
effects on water quality of both storage impoundments and
run-of-the-river or main stream impoundments. In addition
to distinguishing between these two classes of reservoirs,
the principal difference between lakes and impoundments is
discussed.
For many purposes a reservoir may be considered as the
upstream half of a natural lake with the dam replacing the
downstream half. Since both lakes and reservoirs are
physically similar many of the characteristics of lakes are
reproduced in reservoirs. There are two significant
differences however which produce differences in water
quality in downstream discharges.
The first difference involves facilities for
controlling the rate of discharge. Downstream flows may be
reduced to less than natural by controlled releases from
reservoirs and in fact, in certain type operations may be
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reduced to zero for significant periods during the daily
operating cycle.
The second difference is the depth fron which reservoir
discharges are withdrawn when compared with the surface
discharges from lakes. Natural lake discharges are
generally surface waters which are aerobic and therefore
have been subjected to the normal aerobic processes of
natural purification. Water temperatures of these flows
reflect the prevailing average ambient air temperatures.
Reservoir discharges are frequently withdrawn fron deen
within the reservoir. If the reservoir is stratified, this
water may be anaerobic and contain undesirable minerals
resulting in decreased water quality. Water temperatures
may be substantially less than ambient air temperature
reflecting the temperature of the winter and spring runoff
that was stored.
Kun-of-the-river impoundments are located on main
stream rivers and are characterized by relatively low head
aains with impounded waters not extending far from the
natural caannel and water detention times of a few days.
Water velocities are appreciable and in a positive
downstream direction. Passage of water throuah the
reservoir is by displacement usually without significant
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vertical stratification other than that caused by daily
surface warming by the sun. These impoundments are
constructed principally to deepen rivers for navigation in
canalization projects or to provide regulation downstream
from storage reservoirs operated for power generation.
Storage reservoirs are generally located on tributary
streams and are characterized as being relatively deep with
the water surface extending far beyond the natural river
cuannel. These reservoirs have large storage capacity in
relation to the drainage area and generally have several
months uetention time, because of the operation of these
reservoirs passage of water through the reservoir may be
discontinuous and subject the reservoir to large differences
in water level on a seasonal basis. Because of the large
lake level fluctuation, past desians have placed outlets
deep in cue reservoir. Tnese reservoirs are characterized
by thermal stratification generally of the classic three
layer system during the summer warm weather periods.
Primary uses of storage reservoirs include flood storage,
hydroelectric power production and water supply storage.
Recreational use is an important secondary use on many
storage reservoirs.
GO
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Current Governmental Involvement
Several Federal agencies are involved in the
construction of storage and main stream impoundments. ^s
the principal agency responsible for navigation and flood
control on tne nation's inland waters, the Corps of
Engineers constructs both storage and mainstream reservoirs.
Tae Tennessee Valley Authority is also authorized bv the
Tennessee Valley Authority Act to construct dar.s and
reservoirs on the Tennessee River and its tributaries for
navigation, flood control and power production. The Bureau
of Reclamation has constructed storage inpoundrtents to
provide water for the irrigation projects in the western
States. Tne Soil Conservation Service constructs
impoundments in cooperation with State and local agencies
for flood prevention, conservation, development, utilization
and disposal of water purposes. The Federal Power
Commission is responsible for approving non-Federal
development of hydropower and is involved in the approval of
impoundment construction for this purpose. Information on
reservoir projects for hydropower production of a regional
nature is also available from other U. S. Department of
Interior agencies including the Bonneville Power
Administration, Alaska Power Administration, Southeastern
Power Administration and the Southwestern Power
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Administration. The Department of Housing and Urban
Development iias information on reservoirs constructed in
housing projects in which they have an interest. State and
local governmental agencies are also involved in reservoir
construction. Such developments may include recreation
reservoirs and public water supply reservoirs. The name of
the appropriate State and local agency varies from State to
State and therefore must be determined for each particular
situation.
Private development of small impoundments has become
commonplace. Private developers construct suburban housing
developments and recreational weekend communities
surrounding man-constructed impoundments. Private
development of small lakes has also occurred in conjunction
with campgrounds, recreational parks and even pay fishing
lakes.
A survey of the governmental sources will delineate the
large projects and most of the significant smaller projects.
Other projects may require an examination of local
construction permit files or consultation with local
planning commissions.
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Current Practices
Current planning and justification for large reservoirs
involving the Federal Government are generally based on
multipurpose use. The principal multipurpose uses included
are flood control, hydroelectric power production,
navigation, recreation, irrigation water supply, public
water supply, low flow augmentation for water quality or
other special purposes, and fish and wildlife propagation.
State and local projects are also generally multipurpose
with the exception that some water supply impoundments are
reserved solely for that purpose.
FLOOD CONTROL
An extensive network of reservoirs has been constructed
for flood control by the Corps of Engineers and the
Tennessee Valley Authority. The basic theory of operation
of these reservoirs is to reduce storage quantities to a
minimum level prior to the normally wet seasons of the year.
uuring the wet season, outlet flows are kept to a minimum
while excess tributary flow is stored. Following the wet
periods the reservoirs are usually filled to near maxirium
storage levels. The available storage is then used to
maintain normal or increased stream flows, produce
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nydroelectric power when passing through the dan, and
provide recreational opportunities on the reservoir itself.
During the drier periods of the year the level is graduallv
lowered to reach the minimum as the next wet period
approaches.
POWER PRODUCTION
Water storage for power production is one of the oldest
uses of reservoirs. Many small reservoirs have been
constructed to furnish energy to individual mills or snail
communities. Presently designed developments are rarely for
single purpose hydroelectric power production but the
incorporation of this feature is primary at many reservoir
sites.
Hydroelectric power production is generallv used to
meet peak daily loads in conjunction with a steari-electric
facility which supplies the base electric power
requirements. The steam-electric facilities operate
continuously while the hydroelectric power is produced for
4-8 hours to meet peak demands for air conditioning in the
summer and heating in the winter, and other hone and
industrial electric consumption demands. Such peaking power
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operations are the standard operating scheme for many areas
including chat served by the Tennessee Valley Authority.
Sone storage reservoirs were constructed sufficiently
large in comparison with the power denands of the tines to
allow continuous power production operations by adjusting
water turbine operations to conform to the applied load.
'j.\iis cype operation is generally inefficient with greater
economies achieved by using stean generated power for the
base load and meeting peaks with hydroelectric power.
Many of the main stream impoundments also have power
generating facilities. Since the operation of these
reservoirs is frequently for maintenance of a specific pool
elevation, peaking power with its inherent rapid pool stage
fluctuations is not possible. Power production is therefore
limited L>y the incoming river flow and must be marketed on
that basis.
nAVIGA'i'IOiJ
Development of navigation on the nation's inland
waterways is a major use of main stream impoundments. Such
dams are serially located along a stream with the pool of
the downstream reservoir terminating at the toe of the next
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upstream dam. Navigation locks are provided at each dam to
raise and lower river traffic. The use of such canalisation
techniques have been applied on the Ohio River and the Upper
Mississippi River to name two examples.
The dams are operated to maintain controlled pool
elevations for the convenience of commercial barge traffic.
Flow at each dam is adjusted by use of weirs, bv flow
through the electric generating turbines, and by the number
of lockages to maintain the specified pool elevation.
WATER SUPPLY STORAGE
Water supply storage reservoirs include those
reservoirs constructed to supply storage for public water
supply, industrial water supply and irrigation water supply.
Single purpose domestic and industrial water sunnly
reservoirs are frequently snail when compared with other
types of storage reservoirs. These impoundments are
constructed to provide sufficient quantities of water to
augment the incoming stream flows during low flow periods.
Sufficient detention time is generally provided to allow
natural purification processes such as biochemical oxidation
of organics and sedimentation of particulate material to
enhance the water quality and reduce water treatment costs.
GC
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Storage of water for subsequent irrigation use is
responsible for most of the agriculture in the western
States. Large impoundments, exemplified by the reservoirs
on the Colorado River, store water from snow melt and winter
rains and provide irrigation water during the growing
season. Huge complexes of irrigated farms have been
developed to make use of the water which is diverted fron
these reservoirs.
MULTI-PURPOSE RESERVOIRS
Only infrequently are truly single purpose reservoirs
constructed under presently existing conditions. Most
reservoirs include many uses although one use may
predominate.
Modern planning incorporates multiple uses to calculate
the benefits accruing from a proposed project. Costs are
likewise allocated to various projected uses. The final
benefit-cost ratio reflects the total value of the project
as against the cost of construction.
07
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Sources of Pollution
The construction of reservoirs of all types produces
direct and indirect changes on water quality of the
inflowing water. Direct changes include the physical,
biological and chemical alterations that occur during
storage and because of the changed environment from that of
a moving stream to a quiescent lake. Many of the direct
changes to water that occur during storage improve the
quality especially in the aerobic surface layers. Through
the processes of natural purification objectionable
constituents may be removed.
Indirect effects include watershed development which
contribute pollutants and nutrients which may ultimately
degrade water quality in the impoundment. Frequently the
direct changes that occur are also either magnified or
mitigated oy the changed environment from stream to
reservoir.
BASIC RLSHRVOIR HYDRAULICS
Tne ueleterious effects on water quality caused by the
construction of a reservoir or by a series of reservoirs in
a canalization project can best be understood after an
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elementary understanding is acquired of basic reservoir
Hydraulics.
Storage reservoirs in temperate climates frequently
become stratified during the summer and winter with periods
of non-stratification occurring during the spring and fall.
The formation of stable stratification depends on the
density of water. The density of v/ater chancres with varied
temperatures reaching a maximum at 4 degrees Celsius and
decreasing with either an increase or decrease in
temperature from that point.
The classic stratification pattern for summer has a
surface layer, the epilimnion, which is well mixed by wind
and wave action. Beneath tiie epilimnion is a narrow zone of
rapid temperature decline called the thermocline or
mesolimnion, which is characterized by a temperature change
of more than 1 degree Celsius per meter. The lowest zone,
the aypolimnion, is effectively shut-off from atmospheric
reaeration, and has only a small temperature gradient. The
summer stratification is graphically illustrated in Figure
4(a).
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DAM
*
WATER SURFACE
INFLOW
EPILIMNION 30°C
THERMOCUINE ,
(MESOUMNION)
10° TO 30°C
10°C
HYPOLIMNION
PENSTOCK
INTAKE
a) Storage Impoundment
DAM
WATER SURFACE
INFLOW TEMPERATURE NORMAL
u) kun-of-tiie-river Impoundment
figure 4 Thermal Stratification in Reservoirs During Summer Period
70
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The winter stratification of storage reservoirs is
characterized by either ice or water of temperature less
than 4 degrees Celsius floating on water of 4 degrees
Celsius which then extends to the bottom of the reservoir.
Tae iiypolinnion is again stable and is effectively removed
from atmospheric reaeration. Because of low temperatures
aowever uiological activity is low and water quality may not
be substantially impaired during the winter stratification.
The winter stratification is graphically illustrated in
Figure 5.
Tne point of discharge in most storage reservoirs is
near the bottom so that releases can continue to occur when
the water level is low in the reservoir. Thus, hypolimnetic
water is generally released. If anaerobic, this water may
be initially of poor quality because of no dissolved oxygen,
concentrations of odorous constituents and concentrations of
soluDle metals. The quality of the discharged water is
therefore greatly affected by the dissolved oxygen
concentration in tne hypolimnion if withdrawal is effected
from this water mass.
If the dam is constructed so that water can be
withdrawn from different depths, stratification allows the
selective withdrawal of water of better quality. Selective
witndrawal is accomplished through the phenomenon of
stratified flow.
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INFLOW
LENGTH
Figure 5 Thermal Stratification in Storage Reservoir During Winter Period
72
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The thermal stratification of storage reservoirs is
governed by a heat balance taking into account solar
radiation, surface losses by evaporation and conduction, and
the input and outputs of heat by inflows and outflows. The
thermal stratification effects discussed has a dominant
influence on internal flow patterns in the reservoir and
greatly affects outflow water quality.
Main stream reservoirs may exhibit a gradual
temperature gradient with temperatures decreasinq fron top
to bottom. This gradient is caused by the absorption of the
sun's energy in the upper water layers and the existence of
insufficient downstream velocity or wind induced mixinq to
insure complete vertical uniformity. Such a thermal
condition is graphically illustrated in Figure 4 (b). If the
stratification is stable enough to continue overnight or
exist for several consecutive days, water quality in the
lower layers may be adversely affected by declining
dissolved oxygen levels. Downstream quality may be affected
depending on the methods of releasing water and location of
outlet works at the dam.
To summarize, thermal stratification of reservoirs
occurs in both those designed for long term storage and in
main stream reservoirs. The effect is to reduce vertical
73
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circulation and the transport of dissolved oxygen to lower
layers in the impoundment. Without some means to discharge
waters from other than the hypolimnion, downstream water
quality may be impaired.
QUALITY CuANGLS WITHILJ RLSLRVOIRS
Cnemical - Physical Changes
Tne annual cycle of storage impoundments in temperate
climates consists of the winter and summer periods of
stratification which are separated by periods of essentially
uniform temperature distributions from top to bottom of the
reservoir during which the waters freely mix. The periods
of mixing are called the spring and fall turnovers. During
the turnover periods soluble material entrapped in the
hypolimnion is returned to the biologically active near-
surface region. The source of this material is water
inflows, production in the epilinnion, or leaching from the
oottom rauas. Such materials consist of the inorganic
nutrients nitrogen and phosphorus, chemically-reduced heavy
metals such as iron and manganese, and unoxidized organic
material. The nutrients become available to support renewed
primary production. The turnover period freguently
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coincides with the typical fall and spring plankton bloon.s
observed in many reservoirs.
During the turnover periods dissolved oxyqen
concentrations are uniform throughout the denth of the
reservoir. As the reservoir warms followina the sprina
overturn and stratification occurs, the supnly o^ oxygen to
the nypolimnion from atmospheric reaeration is terminated.
As the summer progresses dissolved organic material in the
hypolimnion which includes that present initiallv plus
material settling into ana diffusing from the unper layers,
exert oxygen uenands as bacteria oxidize these materials.
If the organic content is sufficient to cause total
depletion of dissolved oxygen concentrations then anaerobic
conditions become established and water quality is seriously
degraded.
Compounds suca as metallic phosphates and carbonates
whicn are chemically stable and insoluble under aerobic
conditions become soluble and enter solution under anaerobic
conditions. This condition leads to the leaching of
materials from the bottom muds. The bottom muds have an
oxidized surface layer during aerobic conditions which
prevents leaching of underlying anaerobic products. Under
anaerobic conditions this oxidized zone is eliminated and
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compounds are readily leached. Increases in iron, ammonia,
manganese, silica, phosphate and sulfide ions have been
observed in oxygen depleted waters in contact with bottom
muds. Increases in soluble organic compounds also occur.
Since many storage reservoirs withdraw water for
release from near the reservoir bottom, the quality of this
water may be much poorer than that which occurred in the
pre-impoundment stream. Low dissolved oxygen
concentrations, the presence of reduced metallic compounds
and the presence of odorous organic compounds are evidence
of such deterioration.
Main stream reservoirs as a general rule do not become
stratified for extended periods of time. Depending on the
dissolved oxygen concentration gradient (if one exists)
similar leaching from the bottom muds as that in storage
reservoirs may occur. Without stratification and assuming
mixing from top to bottom, the water discharged does not
represent a particular zone and thus the depth of withdrawal
is not critical to water quality.
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Biological Changes
In the process of converting a strean into a reservoir
the biological community must adapt from a moving water
stream system to a still water or lake environment. The
entire biological system may change significantly in storage
reservoirs whereas only minor changes may occur in main
stream reservoirs. Anticipated changes include population
shifts in plankton, rooted aquatic plants, aquatic
invertebrates, and fish.
SITE PREPARATION EFFECTS ON WATER QUALITY
Water quality may be affected by many characteristics
of the reservoir location site. Factors which affect future
water quality include maximum and operating depth range,
reservoir configuration, relation of principal axis to
prevailing wind direction, geology of area, characterif>tics
of tne unuerlying soil, and the type of native vegetation.
Tae characteristics of the underlying soil and the
vegetation tnat remain before inundation are important to
future reservoir water quality. Both the soils and
vegetation require investigation to determine the amount of
organics present in the soil and its state of decay so that
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the amount of leachable color, nutrient release, organic
acid production and decrease in pH can be predicted.
Additional soil analyses can determine the amount of
leachable inorganic salts present which tend to increase the
total dissolved solids in the overlying water. Based on
such determinations, decisions can be made regarding the
necessity of removing organic soils prior to inundation or
using a mineral soil covering of the organic soils to
prevent their undesirable effects.
The chemical, physical and biological reactions that
occur at the soil-water interface are complex and not
particularly well understood. It has been shown however
that these reactions are more of a biochemical nature than
purely chemical or physical. The organic content of the
soil and pre-inundation vegetative cover are responsible
more than other characteristics for the undesirable effects
on the overlying water. The adverse effects caused
originally by freshly inundated soils are reduced with time.
This aging process is a combination of leaching, of organic
destruction and of being covered by sediment transported
into the reservoir. Estimates of the time required for
reservoir bottoms to stabilize so that tastes, odors and
color are not imparted to the water indicate that 10-15
years may elapse. The equilibrium condition is defined as
7C
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the point where reservoir water quality is determined by the
quality of the inflowing water. The effects on dissolved
oxygen concentrations usually are significant for only the
1-2 years with normal reservoir site preparation although
minor effects may occur for substantially longer periods.
RELEASED WATER QUALITY
The water quality downstream from a reservoir is
obviously affected by the design and operations of that
reservoir. If lower quality water is discharged than
previously existed before the reservoir then the effect is
the sarae as that caused by a pollution source.
Additionally, the discharge may be of a temnerature
unnatural for native biological systems. This occurs
frequently uuring trie summer because the hypolinnetic water
released reflects the cooler water stored during the high
flow winter-early spring seasons. Such low temperature
discharges interfere with natural fish spawning cycles as
well as the existence and reproduction of invertebrates and
other lower life forms.
The effects on downstream water users from the effects
of impoundments include increased treatment costs at points
7')
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of withdrawal for water supply use. Taste and odor, color,
iron and manganese concentrations all may be increased above
previous stream concentrations and require treatment for
removal. Inorganic nutrients, principally phosphorus and
ammonia-nitrogen may be present in increased amounts if the
reservoir hypolimnion was anaerobic. These nutrients can
stimulate rooted aquatic plant growth as well as plankton
growth in downstream reaches. Plankton in nuisance amounts
can produce water treatment problems by contributing taste
and odor to water and by interfering with filtration
processes. Both plankton and rooted aquatics reduce the
aesthetic quality of water, reduce recreational aopeal and
pose subsequent oxygen demands on the stream's dissolved
oxygen resources.
EFFECTS ON GROUND WATER
The most important effect of a dam on ground water
quality occurs where the foundation of the structure
provides a substantial or complete cutoff of ground water
flow in an aquifer. Such a stoppage reduces the hydraulic
gradient of the ground water upstream of the dam. This
causes an increased accumulation of pollutants in the ground
water because of slower movement or complete stoppage.
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Another effect is caused by the higher water table
created oack of a dam which extends around the periphery of
the reservoir. The high water table brings the ground water
closer to the ground's surface where the opportunity for
pollution from surface pollution sources nay be increased.
Marshy areas, swamps, and pools also may be created.
.Liven in situations where the dan and its foundations do
not substantially alter the total ground water flow through
the underlying aquifers, the localized effects on ground
water levels and on the original pattern of ground water
flow may nave significant adverse inpacts on ground water
quality. Seepage losses from the reservoir also contribute
to the ground water. If the quality of the water in the
reservoir is better than that of the ground water,
improvement in ground water quality results. Conversely,
seepage losses from a reservoir storing poorer quality water
(e.g., reclaimed water) degrade the ground water.
In certain areas development of lana areas tributary to
reservoirs may constitute major sources of pollution and
nutrient fertilization. On small reservoirs constructed in
conjunction with suburban housing developments direct
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drainage from streets and lawns constitutes the prinary
cause of water quality degradation. On large reservoirs
increases in upstream tributary population and development
on the periphery of the lake shore nust be considered in
projecting water quality although these sources nay not be
of immediate concern.
Suburban development surrounding a snail reservoir can
deteriorate water quality by direct waste disposal through
the use of sewage treatment plants not providing nutrient
removal, discharges from watercraft, run-off from yards and
streets and by infiltration from polluted ground water where
septic tanks are used. Contamination in the feeding stream
upstream from the reservoir intensifies the pollution
problem.
larger reservoirs are also adversely affected by direct
sources but because of the volume of dilution available,
these effects may not be immediately noticeable. Large
direct discharges from industries or municipalities however
can seriously degrade water quality unless adequate
treatment is provided these sources. Nutrient
concentrations from upstream point and nonpoint sources may
accelerate eutrophication processes causing algal blooms and
subsequent dissolved oxygen problems.
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CHANNEL MAINTENANCE
Since one of the principal reasons for the construction
of the main stream reservoir is to maintain minimum depths
for navigational use, channel maintenance becomes a key
feature to maintaining the system. The removal of settled
materials provides an additional benefit by providing
renewed space for the settling of additional sediment
transported by the tributary streams. Such maintenance
generally consists of some method of dredging but may
include channel bank maintenance where affected by wave
action or propeller wash. Water quality is affected by the
dredging operation itself, and by the spoil disposal method
employed.
The dredging operation resuspends silt and other fine
grained material which increases turbidity. These materials
later settle Blanketing downstream sections of the
impoundment. Adsorbed materials, such as organic compounds
and nutrients which travel with these silty materials, may
be released to the aquatic phase either stimulating or
inhibiting stream life.
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NAVIGATION RELATED SPILLS
Any stream which is maintained for navigation is
subject to accidental spills of cargo and fuel while in
transit plus the possibility of catastrophic accidental
spills from shore storage and support facilities. These
potential pollution sources are unpredictable as to tine of
occurrence jjut can be expected from tine to tine. The
effects of these spills can be disruptive to other water
uses and disastrous to aquatic life.
In WASTL ASSI1IILATIVL CAPACITY
Waste assimilative capacity has traditionally been
oased on the uissolved oxygen requirenents necessary to
maintain fish and aquatic life. The calculation of the
dissolved oxygen concentration profile downstream fron a
waste source essentially is a balance between the anount of
oxygen required to oxidize organic material and the anount
of oxygen supplied by atmospheric reaeration. Currently
available formulations for estimating reaeration indicate
that rates are increased by an increase in water velocity
and decreased by an increase in water depths. A reservoir
both decreases velocity and increases depth and therefore
reduces reaeration by both factors. The increased surface
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area of an impoundment increases the available surface area
as compared to the original stream. The increased surface
area increases the opportunity for direct reaeration, for
photosynthetic oxygen production and for wind-induced wave
action. These effects are generally insufficient to counter
the decrease in turbulence caused by the decreased velocity
and the net effect is reduced reaeration (Ref. 1).
The decreased water velocity also provides for
sedimentation of particulate material in waste discharges
usually near the outfall. This material intensifies oxygen
demands near the outfall and reduces oxygen levels even more
rapidly.
The biochemical oxidation of organic material is
generally assumed to be a function of tine. By reducing the
water velocity the distance over which this denand is
exerted is reduced.
The net effect of the reservoir is to reduce the
distance over which dissolved oxygen concentrations are
reduced by the biochemical oxidation of organic material and
to greatly intensify the amount of depletion that occurs
within that reach because of reduced reaeration. To
maintain water quality, less organic material can be placed
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into the reservoir, than was previously placed in the
flowing stream.
For main stream reservoirs the effects on dissolved
oxygen resources are readily calculable using standard
techniques; for storage reservoirs the hydraulics are
complicated and variable and such changes are not as easily
predicted (Ref. 2 and 3).
Types of Pollutants
Water quality changes related to reservoirs are of
concern within the reservoir itself and in the downstream
reaches of the stream which receives releases fron the
reservoir. The water quality at the surface is of
importance for recreational, biological and aesthetic
purposes; that in the hypolimnion because of the effects
that quality of released water has on downstream uses. At
times of non-stratification the existing quality affects all
uses and establishes the mixing of materials which will
determine water quality in both zones followinq re-
establishment of stratification.
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BIOLOGICAL FACTORS
The biological forms in the epilimnion mediate nariy
physical and chemical water quality changes in this zone.
Because of this activity water quality is affected
subsequently in the hypolirinion. Bacteria, plankton, rooted
aquatic plants, invertebrates and fish all contribute and
react to these water quality changes.
The plankton as primary producers in the system use
available inorganic nutrients to develop and sustain their
populations. Increases in nutrient concentrations provide
material for increased plankton numbers. The major
nutrients required include inorganic nitrogen, carbon and
phosphorus. So-called minor nutrients and growth factors
may also be required. Plankton populations generally are
related to nutrient concentrations assuming adequate light
and tne absence of toxic materials.
uense plankton populations directly affect the chemical
quality of water. The process of photosynthesis occurs
during daylight hours. Algae remove carbon dioxide from
solution which causes an increase in pll. The carbon dioxide
is photosynthetically reacted upon to produce dissolved
oxygen and new algal cells. The dissolved oxygen is
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produced in quantities that frequently exceed the water
solubility of this element. At night carbon dioxide is
produced by algal respiration which reduces pll and depletes
dissolved oxygen concentrations below values that would
otherwise occur. These diurnal fluctuations in pll and
dissolved oxygen can have detrimental effects on other
biological life. For example, in extren.e situations
dissolved oxygen levels may approach total depletion at
night Because of plankton respiration.
The particulate waste products of the aquatic community
in the near surface waters eventually becomes trapped in the
aypolimnion. Materials such as dead algae, zooplankton and
fish plus the feces of all living forms constitute the
materials upon which bacterial decay occurs. Bacterial
decay exerts a demand on the hypolimnion oxygen resources
which may ultimately cause total dissolved oxygen depletion.
Rooted aquatic plants along the shoreline of the
impoundment detract from aesthetic qualities, reduce
recreational opportunity for swimming or other water contact
sports, provide protection for insect developnent which may
pose a health hazard, and become a liability on the
reservoirs oxygen resources when death occurs. These plants
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require stable water levels and clear water allowing light
penetration in order to become established.
Organisms in higher trophic levels such as fish,feed
directly on plankton, on their detrital remains in the
oottom muds, or on those organisms that do. "he population
of these Higher organisms depends on the productivity of the
plankton. Detrimental effects on these organisms are caused
jjy dissolved oxygen depletion, pll changes, or plankton-
produced toxins. Such effects occur because of plankton
activity.
Microbiological factors must also be considered.
Tributary drainage, waste treatment plant discharges and
human wastes discharged from water-craft potentiallv
contribute disease-causing organisms. For recreational use
the bacteriological quality must be maintained so that
disease transmission from fecal discharges is minimized.
The fecal coliform test is the standard technique for
determining the sanitary microbiological quality of
reservoir waters.
n i
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AESTHETIC FACTORS
Aesthetic appeal of an area can be enhanced or deqraderl
by reservoir design and operation. Ignoring shoreline
development and concentrating on water quality aspects the
most important factors are the control of acmatic plants;
maintenance of dissolved oxygen, color, turbidity and other
chemical constituent concentrations in the ranqe conducive
to desirable fish and aquatic life maintenance; and
maintaining lake levels sufficiently high during the
recreation season to safely allow reservoir recreational
use. A balance of these factors aid in the enjoyment of the
water resource.
CHEMICAL FACTORS
Maintenance of the water quality in a reservoir for
multiple uses requires control of the water chemistry, of
inputs of waste materials and of any toxic materials.
Common measures of chemical water quality include dissolved
oxygen, color, pH, various inorganic salts, metals,
nutrients and organic compounds including pesticides and
herbicides. Specific levels for these materials are
contained in the various State Water Quality Standards.
Discussion of these materials with recommended levels are
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also available in a book entitled "Water Quality Criteria"
published by the i,nvironnental Protection Agency (Ref. 4).
PHYSICAL FACTORS
Tiie physical factors of water quality include
determinations such as temperature and turbidity which
affect the usefulness of water and mediate other chemical
and biological reactions.
Temperature affects the rate of physical, chemical and
biological reactions. In terms of reservoir hydraulics,
temperature related density changes in water cause the
development of the stable summer stratification with its
pronounced affect on water quality. Chenically, water
temperature effects the solubility of gases with dissolved
oxygen principally being of interest; the solubility of
chenical compounds; and the reactiveness of certain
constituents. Biologically, reaction rates for aquatic
organisms roughly double for every 10 degree Celsius
increase in temperature. Temperature also regulates
reproductive mechanisms and the life process itself.
Temperature is obviously a most important consideration in
reservoir water quality evaluations.
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Turbidity is a measure of the reduction in incident
light penetration caused by suspended particulate matter.
As a generic term its magnitude is measured by
determinations such as suspended solids and secchi disc in
addition to a direct turbidinetric measurement. The
suspended matter in epilimnetic waters may be plankton while
in hypolinnetic waters it may be sediment. In surface
waters turbidity is used as a factor in determining the
depth of light penetration in determining the so-called
euphotic zone or zone of photosynthetic activity. In water
supply uses of various types it is a factor in treatment
costs. In reservoir hydraulics a turbid inflow may be more
dense than certain existing layers and produce a phenomenon
known as an interflow which would insert a layer between
existing water layers and subsequently affect discharged
water quality. Turbidity is both an economic and quality
parameter to be included in reservoir water quality.
Methods of Pollutant Transport
The basic hydraulics of both storage reservoirs and
main stream reservoirs has been previously discussed. The
movement of soluble pollutants through a reservoir coincides
with the hydraulic movement. Particulate pollutants, if
organic, may be biologically solubilized; inorganic
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materials may be indefinitely held up by being incorporated
into the reservoir sedirients. Other factors such as solar
radiation and the reservoir operating schedule influence
water quality in the reservoir itself and the strean
downstream from the reservoir.
Pollutant transport in a strean is genorallv quite
simple as the pollutant travels at the sane rate as the
water itself. Tuis generalization has exceptions as for
example sediment load which varies with respect to the water
velocity. Vhis same essential transport process occurs in
main stream impoundments where velocities are typically
uiscernable and sufficient to maintain particulate matter in
suspension. Stratified storage reservoirs in contrast have
extremely complex hydraulics. Density effects, surface
mixing caused by winds and the level of water release all
bear on pollutant residence tine.
TRAuSPOR'x1 Ii,'TO THE STORAGE RESERVOIR
Discharges directly into reservoirs which include
direct runoff, tributary streams or waste streans are
segregated in the reservoir by their density. Beginning in
the spring as discharges typically become progressively
warmer and less aeiise, the flows form layers above the
J3
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existing cooler waters. Toward fall when inputs become
cooler and therefore more dense than stored water, the
inputs may form interflows between existing layers. Waste
discharges would also tend to be density segregated which in
that case nay include salinity-induced density effects in
addition to thermally caused density effects. Thus the
location of an incoming pollutant depends on the existing
density regime in the reservoir and the density of the water
transporting the pollutant.
TRANSPORT WITHIN THE STORAGE RESERVOIR
The water discharged from a reservoir is the densest
existing water layer above the outlet structure. In storage
reservoirs with fixed deep outlets progressively less dense
water is released during the summer stratified period. The
sequence of release approximates the tine of entry into the
reservoir. This progressive release may be interrupted or
modified by the processes of diffusion or by the occasional
passage into and through the reservoir of more dense
sediment-laden storm water or some other flow containing a
density anomaly. As the fall season approaches, but before
the fall overturn, cooler tributary inflows nay also flow
beneath existing storage and pass through the reservoir
ahead of existing storage. Soluble pollutants which are
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stable (e.g. salts) would be transported in a sinilar
fashion.
Particulate pollutants if of sufficient size, tend to
settle toward the reservoir bottom. These materials settle
at different rates depending on a myriad of factors but may
finally reach the bottom or be retained by buoyant forces
occurring in more dense water layers. Thus a density
segregation of particulate matter also occurs. Particulate
pollutants that reach the bottom may be permanentlv renoved
while those trapped in lower lying denser flows may pass
through the reservoir more rapidly than the initial
transporting water.
Many organic pollutants are biologically degradable and
during the storage provided in the reservoir are destrovecl.
These nay be either soluble or particulate in form but are
amenable to biological attack. These materials are
therefore not transported out of the reservoir but are
decayed.
TRANSPORT OUT OF THE STORAGE RESERVOIR
Older dams frequently were designed and constructed
with low level outlets only. Hewer designs incorporate
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multiple outlets so that water from various levels within
the reservoir can be released. With a multiple outlet
system, water of the best available quality can be withdrawn
to protect downstream uses. This is especially innortant
during the late summer period when normal hypolinnion
releases contain the worst water quality of the year in
terms of dissolved oxygen, nutrients, metals and odorous
compounds. Release of aerated epilimnetic waters avoids
this problem as much as possible.
Hypolimnetic water releases during late summer may
release materials accumulated since the spring overturn.
Such materials may have settled to the bottom and become
biologically solubilized; or become chemically precipitated,
settled to the bottom, and become redissolved under low
oxygen conditions near the reservoir bottom. Examples
include detritus of planktonic origin which decay and
metallic phosphates which become soluble under anaerobic
conditions. Thus hypolinnetic releases contain the non-
reactive dissolved materials contained when the water
entered the reservoir plus those products initally removed
but redissolved.
Epilimnetic releases contain the active biological life
contained in this zone and are generally characterized by
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aigh quality water including substantial concentrations of
dissolved oxygen.
Magnitude and Variation of Pollutant Lffects
Jocumentation of the water quality transformation
caused by reservoir construction has been presented for
several basins. For main stream reservoirs one series of
reports is available for the Ohio River which includes
changes observed following the inital installation of low
aeau impoundments and subsequent replacement by higher head
impoundments . (Rcf. 5 and 6).
Similar studies are available from the Tennessee Valley
Authority for both main stream and storage impoundments.
Monitoring information for each operating year for various
water quality parameters are also available in addition to
special studies performed durinq the year.
Bureau of Reclamation reservoirs also have water
quality scudies available for their reservoirs. Such
studies are required for determining the quality of
irrigation water in addition to nonitorino for recreational
and other uses.
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Reservoirs operated by State and local governnents are
frequently monitored for water quality. These measurements
are available in annual State monitoring system reports or
local water supply annual reports.
la addition to these governmental sources of quality
information, engineering and biological literature is
replete with special water quality studies of reservoirs.
Examples are included in the bibliography to this section.
Water Quality Prediction Methods
Tiie prediction of water quality in reservoirs has been
performed by several methods. Included anona the various
techniques are empirical techniques, hydraulic model
studies, and mathematical model studies. All of these
techniques require field aata for verification or
calibration. Suca surveys include chemical, biolocrical and
physical stuuies to ascertain existing water quality and
establish baseline conditions.
EMPIRICAL T^C
empirical methods are generally developed specificallv
for one reservoir and include analyses of data recorded for
Dfi
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a number of seasons or years. Although simpler analyses are
used, statistical correlations are frequently developed
between input water quality variables, reservoir water
quality and output water quality. Operatinq rules for the
reservoir can be modified based on such analyses to maximize
one set of parameters as opposed to another. Simpler
techniques than statistical methods would include the use of
simple graphs with trend line development. Obvious pro>blens
with such methods include: the applicability to onlv one
site, predictive ability only in the ranqe used for
development, no mechanism to correct for changes in phvsical
conditions, lack of fundamental understandina in reservoir
mechanics, and the extended record required for development.
The principle advantages are the relatively inexpensive
development cost and simplicity in use. Depending on the
precision required such techniques may be adeauate for manv
purposes.
HYDRAULIC MODELS
Hydraulic models range in scope from simple laborcitory
scale aquariums to multi-dam basin models covering several
acres. These models are used to verify dam designs for
hydraulic properties, effects on reservoir stratification o*
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sucn designs, or entire river basin conditions for various
flow regines.
jJata from the models are collected bv using various
tracer and stage-velocity measurerent techniques. The data
are then fitteu to a mathematical formulation for
incorporation into a particular design. These data are also
valuable for evaluating mathematical models as some water
quality parameters can be empirically or theoretically
scaleu from model to prototype.
MATHEMATICAL MODELS
Mathematical models are used for many purposes in
reservoir design and operation. The hydrology of an entire
uasin may be modeled to aid in sizing and locating the
optimum number of reservoirs or the amount of water storage
required to meet certain objectives. Internal reservoir
aydraulics and mixing have also been simulated bv
mathematical models. Frequently these simulations are a
first step in predicting the distribution of pollutants in
the reservoir or to predict the discharge sequence and
quality of stored water. Recently attempts have been made
at ecological modeling. These models begin with assumed
material inputs and ultimately predict plankton and fish
100
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populations. uyuraulic simulations, water quality
constituent distributions, phytoplankton production,
zooplankton controls on phytoplankton populations, and fish
populations are all incorporated in such models.
Tiic scientific basis for water quality and ecological
models is a basic understanding of the thermal
stratification process in reservoirs. Recent research
efforts have extenueu knowledge of the stratification
process to the extent that reasonable predictions of the
internal temperature uistributions can be narie. Using the
system Hydraulics as the basic transoort process, the
chemical, physical anu biological reactions are imposed
using the laws of conservation of mass and from general
kinetic principles. Liquations are constructed for each
water quality constituent with the entire set of actuations
subsequently being solved using numerical techniques
frequently with the aid of the digital computer. The model
outputs include the time and space variations of the
important water quality constituents for water quality
models ana additionally, the populations of principal biotic
species in ecologic models.
predicted concentrations and biological populations
from, the models generally follow the observed trends of the
101
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uata used for verification with nunerical values beina
representative of actual values. For most management
uecisions concerning reservoirs the results o^fer adequate
accuracy and offer a valuable tool for evaluating
alternative water quality protection schemes. Assessments
such as waste input locations, operating rules for the
reservoir to maximize water quality, and the projected water
quality for various alternative uses can be nade using such
models.
WAT£R QUALITY SURVEYS
The use of any statistical or modeling technique
requires adequate information for verification and
development. The usefulness of the various models depends
on the accuracy of tne predictions made which can onlv be
verified by field observations. The basis for the validity
of predictive tecnniques requires the performance o^
intensive water quality surveys augmented by routine
monitoring. Key parameters of water quality require
delineation both temporally and spatially within a reservoir
as well as in the inflows and the outflow. These aata
provide information for compliance with water quality
standards in addition to providing aata for future
improvements in analytical and modeling technology.
102
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References
1. Vanderhoof, R.A., "Changes in Waste Assimilation
Capacity Resulting fron Streanflow Regulation" in
Symposium on Streanflow Regulation for Quality ControjL,
999-WP-30, DHEW, Public Health Service (June, 1^537^
2. Markofsky, M. and D.R.F. Harleman, "A Predictive Model
for Thermal Stratification and Water Quality in
Reservoirs," Water Poll. Contr. Res. Series, 1630DSII
01/71 Environmental Protection Agency (January, 1971).
3. Markofsky, M. and D.R.F. Ilarlenan, "Prediction of Water
Quality in Stratified Reservoirs," Jour, of the Hydr.
Division, A.S.C.E., Vol. 99, No. HY5, pp 729-745 (May,
1973).
4. Anon., Water Quality Criteria, Report of the National
Technical Advisory Cortmittee to the Secretary of the
interior, Federal Water Pollution Control
Administration (April, 1968).
5. Anon., "A Study of the Pollution and Natural
Purification of the Ohio River" Public Health Bulletin
Ho. 143, U.S. Public Health Service (July, 1924).
6. Anon., "Ohio River: Markland Pool, "Investigation by
the Federal Water Pollution Control Administration
During 1957, 1960 and 1963 (Pre and Post Impoundment),
Compiled ana Presented by Ohio River Division, U.S.
Army Corps of Engineers (June, 1968).
LJ3
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Additional Bibliography
1. Water Resources Engineers, Inc., "Mathematical Models
for the Prediction of Thermal Energy Changes in
Impoundments," Water Poll. Contr. Res. Series 16130EXT
12/69 Environmental Protection Agency (December, 1969).
2. Anon., hydraulic Models/ Manual of Engineering Practice
No. 25, American Society of Civil Engineers.
3. Imberger, J. and ii.B. Fischer, "Selective Withdrawal
from a Stratified Reservoir" Water Poll.Contr.Res.
Series, 1540EJZ12/70, Environmental Protection Agency
(December, 1970).
4. Chen, C.W. and G.T. Orlob, "Ecologic Simulation for
Aquatic Environments," Office of Water Resources
Research, U.S. Department of the Interior (December,
1972) .
5. Di Toro, D.M., D.J. O'Connor and R.V. Thomann, "A
Dynamic Model of Phytoplankton Populations in Natural
Waters," presented at a course, Advanced Topics in
Mathematical Modeling of Natural Systems, Manhattan
College, Bronx, New York" (1971).
6. Guarraia, L.J. and R.K. Ballentine, "Influences of
Microbial Populations on Aquatic Nutrient Cycles and
Some Engineering Aspects", Technical Studies Report TS-
00-72-06, Environmental Protection Agency, Washington,
D.C. (May, 1972).
7. McCaw, W.J., III, "Water Quality of Montgomery County
Streams ana Sewage Treatment Plant Effluents; December,
19o9-January, 1973," Montgomery County, Marylanu, Dept.
of Environmental Protection, Division of Resource
Protection (June, 1973).
8. Anon., "TVA Activities Related to Study anu Control of
Eutrophication in the Tennessee Valley," Papers
Discussed at Meeting of the Joint Industry/TxDvernrient
Task Force on Eutrophication, National Fertilizer
Development Center, Muscle Shoals, Ala. (April 29-30,
1970).
9. iirooks, N.il. and R.C.Y. ICoh, "Selective Withdrawal fron
Density-Stratified Reservoirs," Jour, of the Hydraulics
Division, A.S.C.E., No. HY4(Julv, 1969).
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10. Mackenthun, K.M., The Practice of Water Pollution
Biology, United States Department of the Interior,
Feueral Water Pollution Control Administration,
Washington, D.C. (1969).
11. Cnurchill, M.A. and W.R. Nicholas, "Effects of
Impoundments on Water Quality," Journal of the Sanitary
engineering Division, A.S.C.E., No.SAG (Decenber,
1967).
12. Kittrell, F.W., "Tnerraal Stratification in Reservoirs"
in Synposium on StrearafIpv/ Regulation for Quality
Control, 999-^7P-3U, DIIUW, Public ilealtlT^ervice (June,
1965).
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IV. Methods, Processes and Procedures to Control Pollution
Resulting From the Impoundment of Water
Tue principal water quality changes that occur by
transforming a flowing stream into a reservoir are those
related to the reduced water velocity and extended detention
time, and tuose changes affected by thermal stratification
of the stored waters.
Reuuced water velocity enhances sedimentation of
inorganic suspended material and tends to increase water
clarity. Sucn quiescent conditions in conjunction with
increased light penetration and sufficient nutrient
materials are ideal for the production of aouatic plants.
under certain conditions this may lead to phvtoplankton
production while in others rooted aquatic or floatina
aquatic plants may develop. Such production ultimately may
produce organic materials for decomposition in the
aypolimnetic waters or bottom muds following the death of
such organisms.
Vnis brief discussion of changes in water qualitv
causeu by water impoundments demonstrates the typical
problems faced. Available methods, processes and procedures
to ameliorate or mitigate these problems will be presented
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and discussed. A bibliography will be presented to enable a
more detailed presentation of a particular subject for those
contemplating use of a particular method.
Site Preparation
It is generally agreed in the literature (Ref. 1 and 2)
that to minimize changes in water quality caused by natural
materials it is necessary to remove all standing timber,
brush, stumps, logs, structures and man-made debris. Crass
and other forms of iierbage should be mowed with, trinmings
removed just prior to inundation. Additionally organic
mucks from swamps should be substantially removed with the
residual covered with 2 or more inches of clean sand. It is
also desirable to cut channels to pockets within the
reservoir bottom to provide drainage when water levels are
lowered. To protect the sanitary quality of the reservoir
cleaning of barnyards, privies and cesspools should be
performed prior to inundation.
Occasionally, soil stripping is employed to remove
soils with heavy organic content (1% to 2%). This operation
is expensive and of only temporary benefit when compared
with non-stripped reservoir bottoms. Without the effects o^
significant sediment inflows, the effects on overlyincr water
117
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quality are equivalent in 10-15 years as between stripneu
and non-stripped reservoir sites. Seuinent in reservoir
inflows may reduce tiiis ti*ne for equilibrium to occur.
Multilevcl Out!ets
Multilevel outlets are increasinqly incorporated in
storage reservoirs to provide flexibility in the v.'ithcirawal
level for released water. Vwo principal water quality
criteria are used to gage the need for such variable
releases: temperature and dissolved oxygen.
Multilevel outlets provide the ability to withdraw
aerated epilinnetic (near surface) water during periods when
nypolimnetic (near bottom) water nay be low or devoid of
uissolved oxygen. This release procedure provides v/ater of
suitable quality to support fish and aquatic life
downstream.
When dissolved oxygen levels are sufficient throughout
the reservoir, the temperature of the released v/ater may be
critical to support anadrorious fish runs, induce spawning or
to maintain cold water species of fish. Multi-level outlets
provide the opportunity to furnish water of the desired
quality if available at any level in the reservoir.
IOC
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Tne hydraulics of selective withdrawal have been
extensively researched in recent years. It is on the basis
of this theory that nulti-level outlets can be rationallv
designed.
Destratification and Hypolimnetic Aeration
In reservoirs with deep withdrawal points that do not
contain multi-level outlets or any method to release aerated
epilimnetic waters, nethods to provide aerated water at the
withdrawal point provide alternatives to construction of
such facilities. Two principal nethods are possibilities:
reservoir destratification and hypolinnetic aeration without
destratification.
Destratification is most connonly accomplished by
compressed air diffuser aerators or mechanical punnina (Ref.
3 and 4). By either method mixing of the hvpolinnion and
epilimnion is accomplished to destroy the thermally-induced
density stratification. The induced nixing provides aerated
water at all reservoir depths which prevents water quality
deterioration within the reservoir caused by oxygen
depletion anu thereby maintains the quality of water
released downstream. Aerobic conditions inhibit leachina of
color, solubilization of metals and nutrients from the
L03
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uottorn sediments, the production of noxious gases, and
provide for the uistribution of more desirable aquatic life
throughout the affected area.
Compressed air aeration has an advantage in that oxygen
is absorbed directly from the rising bubbles in addition to
the aeration at the surface that occurs because o* the
mixing. However, in deep reservoirs operating costs nay be
greater than pumping because of the necessity to increase
air pressure above the static level of the deoth of water
above the diffusers. Pumping conversely only requires
sufficient energy to lift the water from the water surface
up to the pump (plus minor intake pipe friction losses)
whicu may be only a few feet of head.
Both relatively large and small reservoirs can be
destratified. Under given morphologic conditions a long
reservoir has been mixed for a substantial distance uostrean
from the dam by providing mixing from a single location.
Smaller reservoirs can be entirely mixed (Ref. 3). It is
not necessary to destratify an entire lake to achieve
outflows of good quality water. Only the area near the
outlet's structure may require oxygenation.
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iiypolinmetic aeration is a procedure to provide
oxygenation of the hypolinnion without destrovinn the
existing thernal stratification. The purpose o^ avoiding
the uisturbance of the thermal stratification in to protect
existing cold water in the hypolinnion. This water nny be
required for releases to support anadronous fish runs anil
fish spawning. By restrictina aeration to the hvpolinnion
the tenperature change inherent in ni::inrr is prevented and
tne water quality is protected or enhanced.
Several techniques for accomplishina hvpolirmctic
oxygenation aave been developed. U-tube designs, in which
water is withdrawn fron the hypolinnion, punned to the
surface and returned to the nypolirmion arc a possible
method. Compressed air may be injecteu into the water at
the intake of the u-tube. Injection at this ooint provides
contact time while the water travels to the surface. The
undissolved air is subsequently vented at the water's
surface. In another technique low pressure air or pure
oxygen nay be injected at the surface o^ the U-tube before
returning the water to the hypolinnion. The process
utilizes the increased ayurostatic pressure during the
water's descent to effect oxygen absorption. Care nust be
exercised in operation to avoid creating sufficient
turbulence to destroy the thernal stratification or to
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increase total tiissolveu gases to toxic levels. The
injection of pure oxygen is one method to avoid
supersaturation of other gases (principally nitrogen)
contained in air.
Aeration of Reservoir Releases
In order to discharge water with dissolved oxygen
concentrations necessary to meet water quality standards it
nay be necessary to provide aeration of the reservoir
releases. Proper design of multilevel outlets and other
procedures nay be insufficient to neet downstream
requirements. Several methods of aeratina discharges are
available incluuing turbine aeration by venting, Venturi
tuues ana iiowell-Liunger valves.
The Venturi tube aeration device has not been tested on
full scale reservoir releases and therefore nust be
consiuereu experimental. In one device, air was injected
into the throat of a Venturi section. The air was injected
by taking advantage of the inherent vacuum created bv these
aevices. The maximum efficiency of such a device occurs
with only 0.5 rag/I increases; higher oxygen transfers
required increased water velocity and consenuential friction
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losses. The device may only be efficient on snail flows and
not full size reservoir discharges (Ref. 4).
Turbine aeration makes use of the vacuum created by
water flowing through the power turbines. Air is vented to
the turbines to produce increased dissolved oxygen levels in
the reservoir release. In the older style horizontal-type
turbines existing draft tube vents have been used. These
are frequently incorporated in the turbine to control
cavitation. Oxygen transfer efficiencies of 37% have been
reported with turbine power losses of about 5% (Ref. 5).
Hewer turbine units may have the turbine water wheel at
elevations lower than tail water elevation which has the
effect of producing only snail negative pressures. The
absence of substantial negative pressures is not conducive
to efficient aeration. One solution to this constraint has
been the installation of wedge shaped deflector plates in
the draft tubes slightly below the turbine wheel. The
negative pressure created in the wake of the turbulent flow
past the deflectors is used to induce aeration flow.
Aeration efficiency for water initally 80% saturated with
oxygen varied from 25%-50%. Turbine efficiency was
decreased by 0.83% (Ref. 6).
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The Howell-iiunger valve is a fixed dispersion cone
valve which can be used for reservoir releases to provide
aeration. The Tennessee Valley Authority has performed
extensive evaluation of this device for aeration purnoses
(Ref. 7). The valve produces a spray discharge which is
similar to the common garden hose spray nozzle except that
the cone is fixed rather than adjustable. Aeration
efficiencies were determined during the TVA te.stinrf nroaran
and were defined as the ratio of final dissolved oxyaen
deficit to the initial dissolved oxygen deficit.
Efficiencies of 80% were achieved when exit velocities
exceeded 9 meters per second for a free discharge. Initial
dissolved oxygen concentrations for these tests were less
than 1 mg/1.
In addition to the possibilities for aeration while
passing water through the dan, aeration nay be apnlied in
the tailrace or inmediately downstream. Methods previously
discussed such as U-tube aerators and diffused air aerators
can oe used as well as mechanical surface aerators. Methods
which increase turbulence in the reservoir release increase
aeration. The use of weirs or other devices can be employed
in the tailrace to increase the turbulence.
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Control of Biological_ Nuisance Organisms
Wuisance organisns in reservoirs related to water
quality include excessive numbers of algae and rooted
aquatic plants. The populations of these plants depend on a
myriad of factors including nutrient concentrations and
sufficient light. The most satisfactory and only long term
control of these plants requires the institution of measures
to reduce the causative factors. Nutrient reduction in
inflows, shoreline alteration to reduce the existence of
shallow areas, and the implementation of reservoir operation
scnedules are factors in controlling aquatic plant
populations.
Temporary conc.ro! measures are principally mechanical
or chemical. Operational techniques of fluctuating
reservoir water levels can also be practiced. In addition
to reservoir destratification previously discussed,
mechanical techniques include algae harvestina bv
centrifugation, coagulation and filtration, microstraininq,
and flotation; and the use of snecial cutting machines for
Harvesting rooted aquatics.
Harvesting algae fron natural water bodies by any of
the above methods has not received extensive investiaation.
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The efficiency of such harvesting methods is inversely
proportional to the algal population density. This is
because dilute solutions require additional purinina cost to
recover a given amount of algae. Without a narket for the
removed algae to recover substantially the cost o^ removal
the economics are not favorable to these techniques. There
appears to be little hope of developing an economically
feasible harvesting technique for the relativelv dilute
algal population densities that occur in natural waters.
The development of efficient, specialized cuttinn and
narvesting machines allows the direct removal of rooted
aquatic plants. In addition to the expense of oneratinn- the
machines, disposal of the voluminous plant residue also nur.t
ue taken into account. Various methods have been epnloved
to reduce the volume of the plant material bv compaction or
drying before final disposal.
Chemical control methods use algicides or herbicides to
control plant populations. Attributes of a satisfactory
algicide or herbiciue include: reasonably safe to handle
and apply; kill specific nuisance plants; are relativelv
non-toxic to fish, other aquatic animals and terrestrial
animals at plant-killing concentrations; are sa^e *or water
contact by humans or animals or for withdrawn water uses;
11C
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and are of reasonable cost. Tables 1, 2 and 3 present those
neruicides presently registered in accordance with the
Federal Insecticide, Fungiciue, and Rodenticide Act. These
taoles indicate typical application locations and
limitations. Application rate;s of these Materials should
reflect label instructions to avoid damage to non-target
plant anu animal species.
The suppression of rooted aquatics by water-level
management has been utilized because of its practical
advantages in economy and simplicity. Various kinds of
plants can be controlled by drowning if depth and duration
of submersion are sufficient. Use of lowered water levels
is also efficient to control sone plants although care must
be exercised because other varieties of plants than the
target species may become established while water levels are
down. Flooding following mechanical cutting or herbicide
application may assist in eliminating the return of nuisance
species.
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TABLE 1
Chemical
HERBICIDES
REGISTERED FOR USE
IN OR ON WATER
Sites, Types of
Weeds, Limitations
Acrolein
Anitrole
Amitrole -
Copper sulfate
5H20
Lakes, ponds; algae, submersed weeds.
Do not apply to water used for domestic
purposes.
May use for irrigation and farm uses
3 days after application.
Irrigation canals and drainage ditches.
Do not use treated water for irrigation
until concentration falls to 13.8 ppm.
Site unspecified - cattails. Do not
contaminate water used for domestic or
irrigation purposes.
Drainage ditches, marshes; cattails.
Do not anply where water may be used
for domestic or irrigation purposes.
Drainage ditches, marshes; phragmites.
Do not apply where water may be used
for domestic or irrigation purposes.
Drainage ditches, marshes; water
hyacinth.
Do not apply where water may be used
for domestic or irrigation purposes.
Lakes, ponds, potable water reservoirs;
algae
113
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Chemical
Types of Ueeds,
Limitations
Copper sulfate
chelated
Dalapon
Dehydroabietyl-
anine acetate
Dichlobenil
Dichlone
Diquat
Lakes, ponds, potable water reservoirs;
algae
Industrial ponds.
Drainage ditches, spot treatnent;
cattails.
Do not contaminate water used for
irrigation or domestic purposes.
Lakes and ponds; alqae. Do not apply
to water used for domestic purnoses.
Irrigation canals, ditches; alqae.
Do not use treated water on crops.
Lakes, ponds; submersed weeds.
Apply to water surface. Do not use
treated water for irrigation or for
human or livestock consumption. Do
not use fish for food or feed within
90 days after treatnent.
Lakes, ponds, canals; certain bloom
producing blue green alqae. Do not
use in potable water.
Lakes, ponds, ditches, laterals;
submersed weeds. Do not use treated
water for aninal consumption, swimming,
spraying, or irrigation until 10 days
after treatment. Do not use treated
water for drinking nurposes until
14 days after treatment.
Lakes, ponds, ditches, laterals;
floating weeds. Do not use treated
water for animal consumption, swimming,
spraying, or irrigation until 10 days
after treatment. Do not use treated
water for drinking purposes until.
14 days after treatment.
119
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Chemical
Sites, Types of Weeds,
Linitations
Diquat
(Continued)
Endothall
(dinethy1
alkylanine)
Endothall
(dipotassium)
(disodiun)
Lakes, ponds, ditches, laterals;
enersed narqinal. Do not use treated
water for anirial consunntion, sv;inriinqf
spraying, or irrigation until 10 days
after treatment. Do not use treated
water for drinking nurooses until
14 days after treatnent.
Lakes, ponds, ditches, laterals;
algae. Do not use treated water for
aninal consumption, swinrtina, spraving,
or irrigation until 10 da^s after
treatnent. no not use treated water
for drinking purposes until 14 days
after treatnent.
Lakes and ponds; algae. Do not use
treated water xvithin 7 davs at
0.3 ppn, 14 days at 3.0 ppn.
Lakes and ponds; submersed weeds.
Do not use treated water within
7 days at 0.3 ppn, 14 days at
3.0 ppr1..
Irrigation canals, drainane ditches
weeds. Do not use treated water
within 7 days at 0.3 ppn, 14 days
at 3.0 ppn, and 25 davs at 5.0 pnn.
Lakes and ponds; weeds. Do not use
treated water for irrigation or
domestic purposes within 7 days.
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Chemical
Sites, Tvnes of Tweeds,
Limitations
Petroleum Solvents Irrigation and drainage ditches,
inject into water. Do not con-
taminate water used for domestic
purposes. no not use treated water
for irrigation until emulsion breaks
or waste treated water.
Silvex
Simazine
Sodiun penta-
chlorophenate
2,4-H
Xvlene
Lakes, nonds; emerged floating weeds.
Do not contaminate water intended for
domestic, irrigation, or crop spraying
purposes.
Lakes, nonds; submersed weeds. Do
not contaminate water intended for
domestic, irrigation, or crop
spraying purposes.
Ornamental ponds.
Do not use in water intended for
domestic or irrigation purposes.
Paper mill supply impoundments,
algae.
Lakes, ponds; floating weeds.
Oo not use treated water for
domestic or irrigation purposes.
Lakes, ponds; submersed weeds
(granular).
Do not use treated water for
domestic or irrigation purposes.
Lakes, Ponds; emerged marginal
weeds.
Ho not use treated water for domestic
or irrigation pumoses.
Irrigation ditches, inject into
water. Treated water may be used
for furrow or flood irrigation.
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Chemical
TABLE 2
HERBICIDES
REGISTERED FOR USE
AT OR ABOVE WATER LI'IE
Sites, Types of Weeds,
Limitations
Amitrole
Amitrole
Ammonium
-
Drainage ditchbanks. Do not
contaminate edible crons,
Ditchbanks. Keen livestock
off treated areas.
Bromacil
Sulfamate Around lakes, ponds, potable
water reservoirs and their sunnly
streams; brush. Do not contaminate
water.
Around lakes, ponds, notable wator
reservoirs and their snnnlv stream;,
weeds. Do not contaminate water.
Drainage ditch banks - snot treat-
ment; brush control.
Do not contaminate water or use in
irrigation ditches.
Ditchbanks; weeds. Do not conta-
minate domestic water.
Dinethvl
arsinic acid
Diuron
DSI1A
Erbon
Drainage ditches; weeds.
do not contaminate water us^r! for
domestic or irrigation nurnosr-s.
Drainage ditchbanks.
Ditchbanks, snot treatment.
Do not contaminate water used for
domestic or irrigation numoses.
Drainage ditchb=mks. Do not
contaminate domestic or irrigation
water.
122
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Chemical
Sites, Types of Weeds,
Limitations
Fenuron
Fenac
Hexachloro-
acetone
MCPA
MSI1A
Petroleum
solvents
Drainage ditchbanks; brush control.
Ditchbanks. Do not contaminate
water used for irrigation or
domestic purposes,
Drainage ditchbanks; weeds.
in oil.
Ditchbanks; weeds.
Drainage ditchbanks, spot treatnent,
Do not contaminate water used for
domestic or irrigation purposes.
Ditchbanks, irrigation and drainage,
Do not contaminate irrigation water,
Picloram
TBA
2, 4-D
Non-crop area - outer slope of ditches
only, spot treatnent. Do not
contaminate water used for irrigation
or domestic tmrposes.
Drainage ditchbanks. Do not
contaminate water used for domestic
or irrigation purnoses.
Ditchbanks.
Margins of lakes, ponds; emerged
weeds. Do not use treated water
for domestic or irrigation purposes.
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TABLE 3
REGISTERED FOR UGE
ON HUD BOTTOMS AFTER DRAWDOT 7TI
Chenical
Sites, Types of >7eeds,
Limitations
Dichlobenil
Diuron
Fenac
Monuron
Xvlene
Lakes, ponds; submersed weeds.
Apply to exposed shore and botton.
Drainage and irrigation ditches.
Drain off water, spray noist soil
in ditch. Fill ditch and let
stand 72 hours, then waste contained
water before use of ditch. no not
contaninate domestic water.
Lakes, drainage ditches; submersed
weeds. Drain area and anply to
exposed botton. Do not use treated
water for domestic purposes.
Irrigation and drainage ditches;
drain water off area, snray botton,
fill ditch and hold 72 hours, then
waste contained water before use of
ditch.
Ponds, canals; drain off water and
spray vegetation. Do not refill
for 5 days.
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Control of Adverse Effects on Ground Water
Methods to control ground water pollution caused by
dams include the use of one or several alternatives. The
dam and its foundation could be designed so that there is a
minimum restriction to the down-valley-flow of ground water.
The feasibility of this approach will depend, of course, on
the size and type of dam as well as the geologic conditions
of the dam-site.
In impoundments where the water-level is maintained
such as for navigation the water table upstream from the dam
could be lowered by appropriately placed pumping wells.
Such wells would reduce the opportunity for pollution fron
ground water sources and would reduce the residence tine of
stored ground water. In general, water punped from the;
wells would be of satisfactory quality for any available
local beneficial uses; if none existed, the water could
simply be released downstream from the dam. This procedure
would increase the outflow of salts from the basin,
minimizing accumulation. The drawdown of ground water
occurs naturally in storage impoundments as reservoir levels
decline. Pumping would not accomplish any benefit in these
circumstances.
125
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A more drastic measure would be to minimize potential
sources of pollution in the area upstream of the dam. This
could involve changes in land use, reduction in the
application of agricultural fertilizers, or renoval of
agriculturally-related animals from the area. Justification
for such a measure would require the absolute necessity for
good quality water down gradient.
If the reservoir is to store poor-auality water, a site
should be selected where seepage losses to the ground water
will oe minimal. If sucli a site does not exist, it may be
necessary to wholly or partially line the reservoir bottom
using, for example, compacted clay.
126
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References
1. Fair, G.M. and J.C. Geyer, Water Sunply and Waste-Water
Disposal, John Wiley & Sons, Inc., New York (1954), pp
232-239.
2. Sylvester, R.O. and R. W. Seabloom, "Influence of Site
Characteristics on Quality of Impounded Water", Jour.
Amer. Water Works Assoc., 57, 1528 (December, 1965).
3. Toetz, u., J. William, and R. Summerfelt, "Biological
effects of Artificial Destratification and Aeration in
Lakes and Reservoirs - Analysis and Bibliography,"
Bureau of Reclamation Report REC-ERC-72-33, U.S.
Department of the Interior, Denver, Colorado (1972).
4. Syraons, J.H. Editor, "Water Quality Behavior in
Reservoirs," A Compilation of Published Research
Papers, U.S. Department of Health, Education, and
Welfare, Public Health Service (1969).
5. Wisniewski, T.F., "Improvement of the Quality of
Reservoir Discharges Through Turbine or Tailrace
Aeration," presented in Symposium on Streamflow
Regulation for Quality Control,PubTTcat ion 999-WP-30,
U.S. Department Health, Education and Welfare, Public
Health Service (June 1965).
6. Raney, D.C. and T.G. Arnold, "Dissolved Oxygen
Improvement by Hydroelectric Turbine Aspiration,"
Journal of_ the Power Division, A.S.C.E., Vol.99, Mo. PO
1, Proc.Paper 9707 (Hay, 1973).
7. Elder, R.A., 11.N. Smith, and W.O. Wunderlich, "Aeration
Efficiency of Howell-Bunger Valves," Jour. Water Poll.
Control Federation, 41, 4, 629 (April, 1969).
127
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Additional Bibiography
1. Anon., "Measures For The Restoration ana Enhancement of
Quality of Freshwater Lakes," U.S. Environmental
Protection Agency, Washington, D.C. (1973).
2. Bohan, J.P. and J.L. Grace, Jr., "Selective Withdrawal
from Man-Made Lakes, "Technical Report H-73-4, U.S.
Army Engineer Waterways Experiment Station, Hydraulics
laboratory, Vicksburg, Mississippi (March, 1973).
3. Mackentnun, K.M., The Practice of_ Water Pollution
Biology, U.S. Department of the Interior, Federal Water
Pollution Control Administration (1969).
4. Martin, A.C., R.C. Erickson, and J.H. Steenis,
"Improving Duck Marshes by Weed Control," Circular 19-
Revised, 1-60, U.S. Department of the Interior, Fish
and Wildlife Service (1957).
5. Austin, G.H., D.A. Gray, and D.G. Swain, "Multilevel
Outlet Works at Four Existing Reservoirs," Journal of
the Hydraulics Division, A.S.C.,-Vol.95, Uo.HY 6,
Proc.Paper 6877(November, 1969).
6. Wunderlich, W.O. and R.A. Elder, "Effect of Intake
Elevation and Operation on Water Temperature," Journal
qif the Hydraulics Division, A.S.C.E., Vol.95, ilo.HY 6,
Proc.Paper 6917 (Ilovember, 1969).
7. Deutsch, M., "Hydrologic Aspects of Ground-Water
Pollution, "Water Well Journal, 15, 9, pp 10-39 (1961).
128
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V. Guidance for the Identification and ^valuation
of the Affects of Urbanization
Introduction
Urbanization is the concentration of people and of
domestic, commercial, and industrial structures in a given
geographic area. Urban areas commonly include both suburban
and central city complexes. The rapid trend tov;ard
urbanization is indicated by the fact that nore than two
thirds of the nation's population now reside in urban
centers that occupy about 7 percent of the land area of the
United States. By the year 2000 the urban population nay
include as much as three-fourths of the population.
This concentration of people and their activities
results in a concentration both of water resource demands
and of the wastes produced. Water may be diverted and
conveyed to an urban area from sources hundreds of miles
away. An example is the Los Angeles-San Diego metropolitan
complex which receives water from the Colorado River and
from Northern California. Runoff and infiltration in urban
areas are markedly different than in the original
undeveloped area. Thus, urban areas produce hydrologic and
hydraulic problems connected with development of water
supplies; increases in peak streamflows; and increased
129
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mineralization of water resources due to changes in land-use
patterns.
Extensive research has been directed toward the effects
of urbanization especially directed toward surface water
quality and surface water hydrology. This discussion will
emphasize tne effects on the ground water resource, which
uas not been as extensively recognized. Bibliographic
material for both surface and subsurface material are
included.
Sources of Pollution
Seawater intrusion in coastal aquifers is often
associated with urban areas due to overpunping, reduction in
natural recharge, and sometimes loss of recharge from septic
systems that have been replaced by public sewers. Runoff
from urban areas is heavily polluted, especially the initial
flows. Urban leachate, a source of ground water pollution,
owes its composition to dissolved organic and inorganic
chemical constituents derived from a multiplicity of sources
sucn as the cleansing of dirty air by precipitation, the
leaching of materials from asphalt streets, inefficient
methods of solid waste disposal, and poor housekeening
tecuniques at innumerable domestic and industrial locations.
Urban leachate can be a direct contributor to strean
130
-------
pollution because many urban centers are located in lowlands
adjacent to large streams. In reverse, ground water
withdrawals may permit flow of polluted water from streams
to hydraulically interconnected aquifers. The expansion of
densely populated urban and suburban developments into
former rural or heavily fertilized agricultural areas has
compounded the problem of ground water pollution by causing
a mingling of the effluent from cesspools and septic tanks
with fertilizer contaminated ground water. Moreover, in
many urban and suburban areas, wastes that are accidentally
or intentionally discharged on the land surface often reach
shallow aquifers.
Tae pollutional effects of urbanization chancre as
development proceeds. Initially, large amounts of erosional
debris are produced as the original land surface is
disturbed by construction. In the mature stage, domestic
and industrial sewage, street runoff, garbage and refuse are
the principal sources of pollution, which intensifv with
time.
Pollution from urban areas is not confined to the
immediate area or to the immediately adjacent areas. The
effects often extend for considerable distances in ground
waters as well as in surface waters. A relatively recent
131
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and unique problem that has attracted considerable attention
is the pollution of ground water resulting fron application
of deicing salts to streets and highways in winter. The
region affected is largely the Northeast and the Worth-
Central states. The salt appears to reach the ground water
both from storage stockpiles (Figure 6) and fron solution of
salt that has been spread on roadways.
The problem is widespread, litigation on the matter is
not uncommon, and research on alternative non-oolluting
substances is underway.
Ground water in an urban environment may contain almost
every conceivable inorganic and organic pollutant. A brief
summary by source of the principal potential urban
pollutants is given in Table 4.
132
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Figure 6 Conceptual Mechanism of Ground Water Pollution from Stock Pile Leaching
133
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Table 4. Summary of Urban Ground Water Pollutants
Source
Princinal Potential Pollutants
Atmosphere
Precipitation
Seawater encroachment
Industrial lagoons
Cesspool, septic tank, and
sewage lagoon effluents
Leaky pipelines and
storage tanks
Spills of liquid chemicals
Urban runoff
Landfills
Leaky sewers
Stockpiles of solid raw
materials
Surface storage of solid
wastes
Deicing salts for roads
Particulate matter, heavy metals,
salts.
Particulate matter, salts, dissolved
gases
High dissolved solids, particularly
sodium and chloride
Heavy metals, acids, solvents, other
inorganic and organic substances
Sewage contaminants including high
dissolved solids, chloride, sulfate,
nitrogen, phosnhate, detergents,
bacteria
Gasoline, fuel oil, solvents, and other
chemicals
Heavy metals, salt, other inorganic
and oraanic chemicals.
Salt, fertilizer chemicals, nitrogen,
and petroleum products
Soluble orqanics, iron, manganese,
methane, carbon dioxide, exotic
industrial wastes, nitrogen, other
dissolved constituents, bacteria
Sewage contaminants, industrial
chemicals, and miscellaneous highway
pollutants
Heavy metals, salt, other inorganic and
organic chemicals
Heavy metals, salt, other inorganic and
organic chemicals
Salts
134
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Types of Pollutants
The change in land uses which occurs during the process
of urbanization introduces new and varied constituents to
both the surface and subsurface environments. The addition
of soiae types of pollutants may actually decrease while
otners increase because of the land use transitions
involved. Areas previously used for agricultural crop
production may have received heavier applications of
fertilizers, pesticides and herbicides prior to urbanization
whereas unmanaged forest land may not have received directly
applied materials from nan's activities.
Tiie basic inorganic pollutants added to the land's
surface because of urbanization include the various
constituents of fertilizers such as inorganic nitrogen,
phosphorus anu potassium; constituents associated with hunan
wastes and associated domestic uses including chlorides,
inorganic nitrogen, sodium, and phosphorus; constituents
applied for street deicing such as calcium chloride and lawn
soil neutralizers such as lime. Additional constituents are
added by lawn sprinkling using imported water which include
dissolved solids such as chlorides, sulfates, sodiun,
calcium and magnesium, ileavy metal concentrations also
frequently increase following urbanization.
135
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Organic pollutants include the whole gamut of
commercially available products used commercially and in the
home. Tuese materials reach the surface and ground waters
by direct application or through septic tank - tile field
disposal systems, examples of familiar organic compounds
include aetergents, insecticides, petroleum products, paints
and other surface protection products, and chemicals related
to various industrial or home use applications. Many of
these compounds are sorbed by the soil where they are
detained from passage into the surface and ground waters for
indeterminate time periods. If persistence times for such
materials exceed the time to saturate soil sorption sites,
then ultimately these materials will be added to the local
surface and ground water.
Biological contaminants are also of concern. These are
principally contained in the fecal discharges of humans
whicxi are discharged to the environment through septic tank
- tile field systems or leaky sewerage systems and those of
domestic pets including dogs and cats. Pathogenic
microbiological forms including both bacteria and viruses
and parasites are potentially contained in these wastes.
Another effect of urbanization is the increased water
temperature of both surface and ground waters. Surface
13*
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waters become heated because of increased temperatures of
yards and paved areas which heat incident rainfall. Ground
water temperatures are increased by the percolation of such
waters and by the use and return of well water to cool air
conditioning systems.
Methods of Pollutant Transport
Urbanization grossly alters the hydrology of an area. In
general, the hydrological changes result in a decrease in
tiie natural recharge to underlying ground water unless
compensated for uy artificial recharge. A reduction in
recnarge has an adverse effect on ground water quality if
the quality of the natural recharge was high. The decrease
in recharge is due to the impervious surfaces of an urban
area: houses, streets, sidewalks, and commercial,
industrial, and parking areas, which reduce direct
infiltration and deep percolation of precipitation. Peak
storm runoff and total runoff are increased by urbanization,
however the occurrence of the runoff is over shorter tine
periods, and results in decreased streambed percolation.
Natural streambed recharge is further decreased because of
the lining of natural channels for flood control purposes.
The principal mechanism for ground water pollution
transport in urban areas are infiltration of fluids placed
137
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at or near the land's surface anu leachinq of soluble
materials on the surface, 'i'iie sources of fluius include
aeliberate disposal through wells, pits, and basins, and
seepage from Hundreds or thousands of miles of leakv storm
water and sanitary sewers, water nains, gas mains, stean
pipes, industrial pipelines, cesspools, seotic tanks, and
other subsurface facilities. Some natural treatment of the
fluid occurs as it seeps downward through the soil zone;
however, large quantities of pollutants, particularly the
mineral constituents, may reach the water table in the
uppermost aquifer. From there, the polluted water may move
laterally toward natural discharge areas or toward pumpina
wells.
Magnitude and Variation
Major surface water sources have quality information
available for urbanized areas. Smaller streams draining
localized watersheds frequently do not have such
information. Frequently the local drainage streams, do not
nave flow other than during the annual wet season or
following rainstorms. The effects of urbanization on these
waters is most noticeable when street, drainage and storm
water from sewers constitutes the flow.
138
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Ground water quality information in general is not
nearly as available as surface water quality information.
tVells are frequently sampled upon completion for ciienical
and j->acteriological analyses. In urban areas where few
wells exist and tiiese principally for lawn sprinklinq,
quality analyses are relatively rare.
Information in areas with particularly severe ground
water problems associated with urbanization is available.
For example, extensive efforts have been made to determine
the ground water quality on Long Island, x
-------
specific tnreats to ground water quality fron past or
present practices of waste disposal (accidental or
ueliberate) can be identified, snecial monitor wells nay be
warranted to provide advance warning of pollutants
approaching water-supply wells.
Even though local ground water nay not be a presently
iriportant source of supply in nany cornunities, monitoring
of its ambient quality is highly desirable in order to
uetect degradation and take action to reduce or prevent
further pollution.
Prediction Methods
Prediction nethods for the effect o^ urbanization for
surface waters traditionally utilize basic hydrological
nethods to predict the quantity of run-off produced for
various intensity storns coupled with field survevs of the
pollution sources tributary to the strean. 'Jhe most conrnon
ayarological raodel is the so called "rational nethod" which
takes into acount the inperviousness of the area and the
time of concentration for rainfall to flow to the collection
point, experience factors for determininfT pollutional loads
from storm sewers and direct runoff can be annlied to
determine resulting water quality.
140
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More sophisticated techniques have been devised usinq
tae concept of synthetic hydrology and stochastic processes
to predict expected runoff and resulting water qualitv fron
various intensity storms. Such models are useful for
planning channel capacity requirements as well as justi^yina
treatment of incoming wastes. By projecting changes in
runoff characteristics, the projection of future conditions
is also possible.
Ground water quality prediction models are generallv
much more crudely developed than surface water models.
iiiyaly sophisticated mathematical hvdraulic novels are
available but these lack the ability to preaict mass
transport of adsorbed or partially soluble cornounds because
of the difficult chemistry involved. Additionally, survevn
of ground water conditions are expensive because o^ the
great number of observation wells required to establish flow
directions and existing water quality. Thus models must use
scanty field data for verification or development.
141
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Bibliography
1. Deutsch, II. , Ground Water Contamination and Legal
Controls in Michigan, U.S. Geological Survey Water
Supply Paper 1691, 79 p. (1963).
2. ilackett, J.E., "Water Resources and the Urban
Environment," Ground Water, Vol. 7, Wo. 2, pp. 11-14
(1969).
3. llanes, R. E., Zelazny, L. W., and Blaser, R. E.,
Effects of Deicing Salts on Water Quality and Biota,
highway Research Board, Report 91, 71 p. (19707.
4. Leopold, L>. B., Hydrology for Urban. Planning—A
Guidebook oil ilydrologic Effects of Urban Land Use U. S.
Geol. Survey Cir. 554, 18 pp. fl^V) .
5. Nightingale, H. I., "Statistical Evaluation of Salinity
and titrate Content and Trends Beneath Urban and
Agricultural Areas—Fresno, California, "Ground Water,
Vol. 3, MO. 1, pp. 22-29 (1970).
6. Perlmutter, 1J.M. , and Guerrera, A.A., Detergents and
Associated Contaminants in Ground Water at Three"
Public-supply Well Fields~~in SoUthwestern^Suffolk
County, Long Island, New York,' U.S. Geol. Survey Water
Supply Paper 2001-B, 2T~pp. (1970) .
7. Pluhowski, E.J. , Urbanization and its Effects on the
Temperature of Streams on Long Island, IJew York U.S.
Geol. Survey Prof. Paper 627-D, 103 r>p.~TT9/0).
d. Seaburu, G.E., Effects of Urban Development one Direct
Runoff to Ease Meadow "Brook, Uassau County, Long
Island, IJew York, U.S. Geol. Survey Prof. Paper 627-B,
14 p. (lW5)~
9. Soren, J. , Ground Water and Geouyurology i_n Queens
County, Long Island, d.Y. U.S.Geol. Survev Water-
Supply Paper 2001-A (T9TO).
10. Varrin, R.O. and Tourbier, J.J., "Water Resources as a
Basis for Comprehensive Planning and Development in
Urban Growth Areas," Internationa1 Synposiura on Water
Resources Planning, Mexico City, Vol". 2, 33 pp. (1970) .
142
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11. Wikre, L>., "Ground Water Pollution Problems in
Minnesota," Report on Ground Water Quality
S ubconuait tee, Citizens Advisory Conrnittee, Governor's
Lny ir o nine n't a 1 Quality~Councily Water Resources Center,
Univ. of Minnesota, pp. 59-78 (1973).
12. Butler, S., Engineering Hydrology, Prentice-Hall, Inc.,
juutier, b., engineering iiyurpi
Englewood Cliffs, J.J. (1957) .
13. Toda, U.K., Ground Water Hydrology, John Wiley & Sons,
Inc., New York, N. Y. (1959) . ""
14. Anon., "Urban Water Resources Research." A study by
ASCI; sponsored by Office of Water Resources Research,
U.S. Departnent of the Interior (1968).
143
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VI. Processes, Procedures _and Methods to Control Pollution
Resulting from Urbanization
The control of the effects of urbanization on surface
water runoff has received considerable research attention
especially in the area of storm water overflow. Potential
control methods nave been suggested and in sone cases
demonstration projects have been performed to evaluate such
techniques (Ref. 1, 2, 3).
The effects on ground v/ater caused by urbanization have
not received an equivalent anount of research effort.
Suggested control techniques in this report must in some
cases rely on judgment rather than proven techniques.
The protection of urban water resources, both surface
and subsurface, can be divided into 3 major categories:
regulation of land use by zoning or other legal means; the
maintenance of adequate waste collection, waste management
and general environmental sanitation; and public education
to minimize inadvertent pollution by maintaining public
awareness of the environmental effects of various actions.
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Regulation of Lanu Use
One method of controlling the evolution of pollutants
from urbanization is to control the type of land development
that occurs. Such control can be exerted through zoning,
uuilding codes or other regulatory neasures. Guch measures
control the resulting population density, industrial
activity, waste disposal technology used and the amount of
impervious areas created by new roads, parking lots and roof
areas.
Applicable legal control methods must be tailored to
the requirements of the particular geographic area. Land
use control measures for an area which furnishes the
recharge to a principal aquifer or which forms tiie immediate
drainage area for a water supply reservoir require different
control measures than for other areas.
In the area of local codes and permits, ground water
protection can be instituted by the use of controls
requiring the proper plugging of abandoned wells. Although
the pollution caused by abandoned wells within urban areas
has never been assessed, the use of such wells as drains or
for the disposal of other liquid materials can pollute local
ground waters.
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Regulations can also be designed to control the
stockpiling of chemicals in such a manner as to prevent the
leaching of these materials into local streams or ground
waters. Storage on impermeable platforms, leachate control
and treatment, and the provision of adequate covers are
methods to control possible pollution fron these sources.
Another code provision to protect ground water quality
and to avoid surface nuisance in many other situations is
the abandonment or prohibition of new installations of
cesspool and septic tank systems in densely populated areas.
Such systems can be replaced by sanitary sewer systems.
Waste Managementand Environmental Sanitation
Once urbanization has occurred, the prevention of waste
materials generated within the community from polluting
local streams and ground waters requires attention to waste
management and general environmental sanitation.
In addition to the proper operation of point sources
such as waste treatment plants, provision for the
collection, by means of drains and wells, and subsequent
treatment of leachate from landfills or other storage, or
treatment ponds or basins can minimize ground water
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pollution. The necessity for such treatment operations can
be combined with inspections to maintain adequate
"housekeeping" practices at locations employing land storage
or disposal of wastes.
The provision of frequent solid waste collection and
care to Keep the collected material contained within the
collection vehicle nelps to keep material fron being flushed
into local streams following rains. This practice in
conjunction wita thorough and frequent street cleaning
reduces the pollutant strength in drainage from urban areas.
In areas where salt is applied to streets to control
snow and ice, such use should be minimized to the amounts
required for safety. Reductions may be accomplished in some
cases by the use of clean sand in conjunction with the salt.
Public Education
Assistance from the public in controlling potential
sources of surface and ground water pollution can be a major
factor in reducing the pollution effects of urbanization.
This assistance can be fostered by education programs
administered through schools, community organizations,
public seminars and public service announcements in the
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local media. Such programs can emphasize good
"housekeeping" practices to reduce litter, publicize
procedures for optimal application of lav/n fertilizers and
chemicals to minimise runoff or leaching, and emphasize the
following of label instructions for use and disnosal of
commonly used household chemicals.
In the process of alerting the public to specific
things they can do to reuuce pollution, an overall awareness
of environmental protection is fostered which nay carryover
to prevent pollution in other areas of activity.
Reduction of Downstream or uown-Gradient Uffacts
In areas where ground water furnishes substantial
quantities of the water used, aquifer denletion because of
the loss of recharge area through urbanization is a serious
problem. Ground water basins can be recharaed usinq high
quality surface waters which may be imported from other
basins or jjy using nighly treated waste effluents. The
source and quality of the recharge water depends on the
subsequent aquifer use that is being protected.
The recxiarge of ground water with high quality water
aas an added Benefit in situations where ground water
14d
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sustains the base flow in local streans. When this water
infi.l trates it provides dilution water in lower strean
reaches for both organic and inorganic materials and helns
co maintain water quality for later uses.
14
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References
Sartor, l.o. and G.B. Boycl, "Water Pollution Aspects of
Street Surface Contaminants", Environmental Protection
Agency Technology Series, EPA-R2-72-081, U.S.
Environmental Protection Agency, Washington, D.C.
(Nov., 1972).
Anon., "Water Pollution Aspects of Urban Runoff"
Prepared by American Public Works Assoc., 11030 DilS
01/69 Water Pollution Control Research Series, U.S.
Environmental Protection Agency, Washington, D.C.
(January, 1969).
Cleveland, J.G., G.W. Reid, and J.F. Harp, "Evaluation
of Dispersed Pollutional Loads fron Urban Areas," Ff-TPCA
Proj. No. 16090 DBX, U.S. Department of the Interior,
Federal Water Pollution Control Administration (April,
1970).
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VII. Guidance for the Identification and Evaluation of the Nature
and Extent of Dredging and Dredged Material Disposal
The purpose of this section is to indicate potential
pollution problems associated with the general aspects of
dredging and dredged material disposal. This section
provides information that, when considered in the light of
local conditions, will provide an indication of the kinds of
measures that may be useful in a program to control
pollution resulting from dredging and disposal activities.
Problems associated with dredging or dredged material
disposal may be minimal and may not adversely affect water
quality under conditions at a given location.
It is not the intent of this section to provide
sufficient detail for selecting practices for specific
geographic areas, water courses, or individual dredging
operations. Expertise, well-founded in the application of
dredging and disposal techniques, must be brought to bear in
design of the final control plan.
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Cu r r en t Invoj.vement
Tue Corps of Engineers has been concerned with the
development and maintenance of navigable waterways in the
united States ever since Congressional Authorization was
received in 1824 to remove sand bars and snags fron major
navigable rivers. Tne Code of Federal Regulations, '.Title
33, Chapter II, Part 209 assigns to the Corps of Engineers
responsibility for enforcement of the principal laws for
protection and preservation of navigation and navigable
waters with respect to work or structures in or over such
waters. Hot only is the Corps of Engineers responsible for
its own operations in navigable waters, it is also
responsible for issuing permits for such activities by other
Feueral agencies, State or municipal governments, and
private citizens or corporations, all of which are subject
to the provisions of the laws for protection and
preservation of navigable waters.
Recently enacted laws indicate the public's increasing
awareness and concern over the possible adverse
environmental effects associated with dredging and dredged
material disposal. The national Environmental Policy Act of
1^69 requires a detailed statement of environmental iraoact
of proposed new navigation projects and projects reguiring
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maintenance dredging. The Rivers anu Harbors Act of 1970
(Public Law 91-Gil) authorizes the Secretary of the Arnv,
acting through the Chief of Engineers, to construct,
operate, and maintain contained disposal facilities to
nandle polluted dredge material from the Great Lakes. The
1970 Rivers and Harbors Act, Sec. 123(i), also authorizes
the Corps of Lngineers to initiate a comprehensive
nationwide program of research, study, and experimentation
to provide more definitive information on the environnental
impact of dredging ana dredged material disposal and to
develop new or improved alternative disposal practices. In
a report entitled "ocean Jumping A National Policy"
submitted to the President in 1970 by the Council on
Environmental Quality it was recommended that ocean dunning
of harmful forms of dredged material be phased out as soon
as alternatives are available that do not excessively
increase costs. The report also recommended that dunning of
unpolluted material be regulated to prevent damage to
estuarine and coastal areas. The development of guidelines
for selection of dredged material disposal sites in the
navigable waters by the Administrator of the Environnental
Protection Agency is authorized by the Federal Water
Pollution Control Act /Amendments of 1972 under Section 404.
Til is Act gives the Administrator authority to restrict the
use of any defined area for dredged material disnosal.
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To date over 3b,000 kiloneters (22,000 miles) of
waterways have been modified for connercial naviaation and
over 30,000 kilometers (19,000 miles) of waterways and some
1,000 aarbor projects are currently beina maintained by the
Corps of Engineers. The total annual quantity of material
removed averages about 229 million cubic neters (300 million
cubic yards) in maintenance dredging and about 61 million
cuuic meters (#0 million cubic yards) in new work dredging.
Total annual costs currently exceed $150,000,000 (ref. 1).
Volumes of material produced by private dredging have been
estimated to approximate the total annual volune of Corns
dredging. The volume of material removed at a single
project may vary from a few thousand cubic meters in a
aarbor maintenance project to many millions of cubic meters
in channel development projects. Variation in the nature of
the dredged material ranges from clean sand and gravel; to
organic muck and sludge of natural origin; or to municipal
and industrial waste sludges or any combination thereof.
The distribution and characterisation of the material
dredged is illustrated in figures 7,8 and 9. The
approximate average annual quantity of material dredged
separated into types (i.e. mud, clay, silt vs. organic muck,
sludge, etc.) is presented in Figure 7 broken down by each
Corps of Engineers District. Figures 8 and 9 present for
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each District an estimate of the amount of polluted and non-
polluted material removed in maintenance dredging ooerations
and the type of area used for final disposal. Similar
information is unavailable for private dredging operations.
155
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Current Practices
Dredging is a process in which sedinents are removed
from the bottom of streams, lakes, and coastal waters,
transported via ship, barge, or pipeline, and discharged to
land or water (Kef. 1). The usual purposes of dredgino are
to maintain, inprove, or extend navigable waterways and to
provide construction materials such as sand, gravel, or sea
shell.
Methods available for dredging can be classified as
either mechanical or hydraulic. Mecaanical dredges are
analogous in operating principal to lana-based excavation
equipment sucn as the uragline, shovel, or trenching
macaine, and can be operated from either dry land or from
above the water's surface. Hydraulic dredges emnloy a pump
to lift the material from the bottom and transnort it by
boat or through a pipeline, to the point of disposal.
Hydraulic dredges of various configurations can be employed
depending on the location of the operation and the nature of
the particular materials to be removed. The principal
concern in the design of dredging operations is generally
with the volume of material to be removed and the locaition
of the disposal site. Consideration of the potential
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environmental consequences has increase^, markedly in recent
years.
Sources and Types of_ Potential Pollutants
In order to assess the pollution potential of dredging
and disposal of bottom material, a basic understanding o^
the types and sources of sediment and sediment contaminants
is required. Basically, the types of contaminants found
associated with the bottom sediment are no different than
the constituents found in various industrial and domestic
wastes or found occurring naturally. The types of materials
encountered can be categorized into inorganic nutrients and
biostimulants such as phosphates, toxic materials such an
metals, organic materials such as peat or sewage sludge, and
bioaccumulatory agents such as pesticiues. In addition to
the categorization of contaminants affiliated with bottom
sediment, the sediment soil particles are usually classified
by grain size into silt, clay, and sand, as well as into
various ill-defined groups such as mud, peat, organic muck,
and municipal and industrial sludges.
Overland runoff and accompanying sheet and gully
erosion are often a major source of suspended solids. Plant
nutrients and pesticides applied to the topsoil in
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agricultural regions, or applied to lawns and gardens in
municipal areas, nay become attached to soil particles and
be transported to the water. Other sources of suspended
solids include bank erosion, bed erosion, other natural
sediment suspension processes such as wave action, and
various industrial and domestic sludges. Various dissolved
chemical constituents, including a large variety of
pollutants, often become sorbed on suspended silt and clay
particles which subsequently settle to becone sediments.
Disturbance of the bottom seuinent, such as by dredging
operations, increases the exposed surface area of these
sediments. Tims the potential for sediment-related
contaminants to leach into the overlying water is increased.
In tiiis sense, then, dredging raay be considered as a
potential source not only of suspended sediments, but of
dissolved pollutants as well.
Effects of Dredging & Disposal Operations
AQUATIC DISPOSAL
The environmental impacts associated with dredging are
taose resulting from the removal of bottom material and its
subsequent disposal. The physical alterations resulting
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from the removal of bottom material include changes in
bottom geometry by the creation of deep water regions,
creation of new open water areas, changes in bottom
suostrates and biological habitats, alterations in water
velocity and current patterns, changes in future seciinent
distribution patterns, alteration of the sediment—water
interface with the potential subsequent release of
biostinulatory or toxic constituents, and tiie creation of
increased turbidity.
Direct effects of dredging on biological corununities
and/or water quality are the result of the physical
disturbance and associated chenical pollutional effects on
the aquatic biota. The principal concern is ordinarily with
tne short-terra direct effects on biological communities but
long-terra effects should not be ignored. The long-tern
environmental impact of dredging is the subject of several
investigations including the Jredged Material Research
Program ueing conducted by the Corps of Engineers at tiie
Waterways i-xperinent Station in Vicksbarg, Mississippi. The
direct effects, nowever, are usually confined to the project
area. The possibility of benthic extermination, or, at a
minimum, extensive damage, is often greater in those locales
where "new" work has been instituted rather than in old or
maintenance areas. A primary reason for this difference is
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that often the substrate in such previously dredged areas is
not conducive to benthic recruitment.
The most common adverse environmental effects
potentially associated with spoil disposal include:
turbidity, which is aesthetically displeasing, reduces light
penetration, flocculates planktonic algae and decreases
availability of food for aquatic organisms; sediment build-
up, which could uestroy spawning areas and snother benthic
organisms, reduce bottom habitat diversity, and reduce food
supply and vegetative coverings; and oxyqen depletion which
suffocates organisms in the area and releases noxious and
undesirable materials such as methane, sulfides, and metals.
Increased sediment resuspension is conmonly associated
with dredging and spoil disposal operations. Disturbance of
the channel, harbor, estuary, lake or other water body
results in the resuspension of solids in the dredged area.
These vary in physical, chemical and biological character
and may result in both short-term and long-term effects on
tiie quality of water at the site, or at times, at some
distance from the actual operation. If these solids are
composed of a large amount of very fine clays, silts and
organic materials, the resulting increase in turbiuity nay
effectively reduce light penetration and subsequently impair
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primary food production necessary to the survival of higher
organisms. Turbidity created during dredging can have
harmful effects on fish. These adverse effects may include
reduction of gill function, impairment of swimming ability,
reduction of rate of growth and increase in susceptibility
to disease.
Toxic materials and biostinulants such as heavy metals,
phosphates, and pesticides sorbed or otherwise incorporated
with sediment particles raay be solubilized during dredging
and resultant sediment resuspension, and thus degrade water
quality. In some instances exposure of organic materials
resulting from disturbance may reduce the dissolved oxygen
content of the water. Total oxygen depletion in turn can
suffocate organisms and cause anaerobic decay which may
release methane, hydrogen sulfide and other toxic gases,
further degrading water quality.
Sorbed constituents may give rise to loner-tern
pollution effects in water. Prior to disturbance, the
sediment with its sorbed chemicals has a minimum exposure to
the overlying water. Consequently the release of sorbed
material is very slow inasmuch as detachment nomallv only
occurs at the sediment-water interface. Desorption is the
release of chemical constituents from the surface of
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particles including colloidal silts and clays. Inasmuch as
the rate and amount of constituent desorption nay be
uependent on uottom sediment movement, dredging operations
have the potential for increasing desorption. Conversely,
it is also possible that the increased exposure of sedinent
surfaces due to dredging and disposal operations mav
increase the rate and extent of sorption of some materials
thus reducing dissolved concentrations of such pollutants.
The most adverse effects of sedinent on the aquatic
ecology may result from maintenance dredging and snoil
disposal where the volume of silt, clay, mud, organic nuck,
sewage and industrial sludges, together with municipal and
industrial debris is high. Materials from maintenance
dredging may also contain considerable amounts of heavv
metals, sulfides, phenolics and other toxic elements.
Sediments uredged from previously undisturbed areas are
ordinarily of relatively high chemical and physical quality
inasmuch as their composition is similar to that of the
geologic strata which they represent. These sediments are
primarily sand, gravel, rock particulates, clay and shale.
Contamination by organic and toxic materials, nutrients,
pesticides and municipal-industrial wastes may be slight or
even absent, in "new" work areas.
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LAND DISPOSAL
On-lanu dredged material disposal sites, unless
carefully chosen, may be instrumental in polluting both
adjacent water bodies and the ground water environment
underlying the disposal site. In addition to objectionable
odors, fine grained spoil masses may retain their high water
content and remain slurry-like for considerable periods of
time. This condition may result in a high degree of
instability, particularly in low lying marginal areas.
Following such disposal operations the foundation conditions
in these areas often remain unsuitable for residential,
commercial, and industrial construction.
Spoil is often placed near or adjacent to urban centers
or in congested areas as a land fill material. In the past
many fill areas developed in an unplanned fashion as a
result of a secondary or indirect (by-product) effect of
dredging. In recent years such fill operations have been
intentionally performed to reclaim or improve land. This
practice is proceeding at an accelerated rate. Under such
conditions spoil is confined or contained by various neans
which tends to regionally limit destruction that previously
occurred in unconfined areas of land disposal.
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Suburban development involves land that is scarce and
costly. Foundation conditions are generally connetent,
allowing spoil to be placed to considerable heights. There
are, however, coastal community, coastal resort, and other
areas where poor foundation conditions prevail. Disposal in
these locales is often aggravated by poor drainage and a
shallow water table.
In the initial stage of a new fill, seepage out of the
fill area may be excessive and should be controlled if
possible. Seepage through and beneath containment dikes
should be analyzed to determine if a pollution potential
exists and if so, to identify those pollutants and measures
to control them. The extent of possible groundwater
contamination should also be established and remedial
measures applied. If the spoil contains a high percentage
of fine-grained organic material, it usually yields a highly
compressible, weak (incompetent) foundation. The unstable
condition is further aggravated when the fill is placed on
wet, organic and compressible subsurface soils.
Where spoil disposal occurs in a containment area,
proper design consideration must be given to outlet
structures such as outfalls and return ditches that
discharge and convey the fluid fraction of the material.
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Viie return flow is often contaminated ana raay contain a high
percentage of suspended solids, dissolved chemicals, and
sorted pollutants. The removal efficiency of these solids
and associated pollutants in the fill area is often verv low
uue to limited retention tine. A large percentaae of the
escaping solids are colloidal and essentially impossible to
remove uy relatively inexpensive, conventional procedures.
Withouc proper controls being incorporated, channelization
at tne outlet worJcs and further erosion of the land surface
jjy indiscriminately discharged water may occur.
jJamage to the ground water province beneath and
adjacent co fill areas occurs through the leaching o^
soluule minerals, chemicals, nutrients and toxic substances.
Such leaching is an ever-present hazard associated witli any
dry land spoil disposal operation. Once contaminated, the
aquifer may be damaged "permanently" or, at best, long-term
and may result in the ultimate abandonment of water wells in
the vicinity. Potential adverse water quality effects on
aquifers underlying a proposed fill area should be carefully
evaluated prior to initiation of spoil disposal.
Potential sources of ground water pollution associated
with uredging and dredged material disposal can include:
the breaching of aquicludes which results in the direct
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introduction of saline or contaminated surface waters to an
underlying aquifer; changes in the surface water hydrology
or circulation patterns with a subsequent seepage of
contaminated surface waters to the ground water regime; and
infiltration of polluted seepage and leachnte fron land
ueposited spoil.
Prediction Metnqds
Prediction of the potential for water pollution fro",
dredging and disposal operations requires consideration of a
nuuber of interacting factors. These include the hyuraulics
of the project area and the waters adjacent to the disposed
material, the chenistry of the spoil material, the chenical
and physical character of the newly exposed surface, and a
knowledge of the involved biological communities.
Prediction of the flow patterns and associated bank and
bed scouring, silt deposition, and flooding is facilitated
uy hydraulic model studies such as those conducted for manv
years t>y the Corps of Engineers. Mathematical models to
predict effects from hydrographic modifications have been
developed by many agencies including the Unvironnental
Protection Agency, Corps of Engineers and the Ceolocrical
Survey.
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Comparative field studies of the effects of dredging
and dredged material disposal on aquatic biota have recently
been undertaken. Tne number of these types of studies will
no doubt L>e greatly increased in the future.
In those instances involving the scalping of an
aquifer, or other alteration of the flow of ground water,
iiydrogeological investigations are also required to predict
the detrimental effects which may involve surface geological
mapping, stratigraphic drill core analyses, punning tests
and mathematical or analog modeling.
If the spoil disposal is into water, the fines and
other solids and associated sorbed pollutants will be
carried in the direction of water current movement. In a
river, the uownstream effects of these materials are a
function of such factors as the quality, particle size,
soluuility and particle density of the sorbed pollutants and
rhe current velocity, and amount and type of turbulence of
the river. Additional factors affecting sediment travel are
the slope of the channel, the irregularity of stream bottom,
tne uepth, and the discharge volume. The rate of change of
velocity is also an important factor regarding the range of
seuiment travel. Velocity decreases promote settling,
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whereas velocity increases encourage scouring and
resuspension of sediments.
Spoil discharged into large water bodies such as
estuaries, harbors and bays may form temporary turbidity
plumes whose extent and geometry are primarily a function of
the water movements in which they are transported.
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References
1. Boyd, M.B., R.J. Saucier, J.W. Keeley, R.L. Montgomery,
R.D. Brown, D.B. Mathis and C.J. Guice, "Disposal of
Dredge Spoil Problem Identification and Assessment and
Research Program Development." Tech. Report H-72-B.
Office, Chief of Engineers, U.S. Arny Engineer
Waterways Experiment Station, Vicksburg, Mississippi.
November 1972.
2. O'Neal, Gary and Jack Sceva, "The Effects of Dredging
on Water Quality in the Northwest." Region X,
Environmental Protection Agency, Seattle, Washington.
July 1971.
3. Pierce, Ned D., "Inland Lake Dredging Evaluation."
Tech. Bulletin Wo. 46, Department of Natural
Resources, Madison, Wisconsin. 1970.
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VIII. iiethods, Processes and Procedures to Control
Pollution Resulting fron Dredging and Dredge Spoil Disposal
Dredging may result in pollution at both the removal
and disposal sites. Vhe direct water quality effects of
dredging, especially those confined to the project, may be
short-terra and may include: turbidity effects, sedinent
uuilu up, oxygen uepletion, removal of substrate materials,
and resuspension of solids. For the most part these effects
are inseparable from the dredging operation and occur to
some degree in every project. It is possible, however, with
good engineering practices, to nininize and localize the
adverse effects both at the removal and disposal site.
Vhe information presented in this section relies
neavily on that developed by the Corps of .engineers as
published in the report entitled "uisnosal of Dredge 5Jpoil-
Probleri laentification and Assessment and Research Program
Development," Doyd, M. B. et. al. 1972 (ref 1).
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Treatment Before and During Dredging
Uredgeu materials vary widely in both physical and
chemical characteristics. While nany types nay be
considered polluted, major problems are generally linited to
highly organic, petrochemical-laden silts and clavs and
domestic and industrial sewage sludges found in waterways
bordered by heavy population or industrial concentrations.
high concentrations of heavy metals may also be associated
with these materials.
AL; RAT i OH
Aeration can be utilized to stabilize (oxidize) highly
organic material. Successful utilization in dredging will
uepend on proper application of established sanitary
engineering principles including sufficient oxygen/water
interaction over an adequate time period. Mechanical
aerators and pneumatic bubbler systems have been used
experimentally in the pilot programs. In concent,
satisfactory aeration by mechanical or bubbler systems using
air or oxygen could possibly be performed within either a
confined land disposal site or an enclosed open water area
bounded by a silt curtain. Basically, the process involves
spraying, by sidecasting or similar method, the material
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into a sufficient volume of water surrouncieu by a silt
carrier. The spoil would then be subjected to prolonged
aeration in an effort to satisfy the associated oxygen
demand. It is conceivable that aeration could be folloveu
uy coagulation. If this systen proves practical, dredginc-
could be used to both inprove the area from which the
material was removed by removing unwanted organic substances
and improving overall water quality by satis^yinn the oxygen
demand associated with organic material. Aeration offers
the potential to deal with highly polluted spoil in a
progressive, environmentally compatible manner.
Aeration of bays, harbors, and other areas has been
suggested as a possible method of treatment where organic
sludges are responsible for noxious anaerobic conditions.
The method, if ultimately proven practicable, could result
in changeover from anaerobic to aerobic decomposition and
conceivaoly modify long-term ecologically unuesirable and
aesthetically displeasing conditions. Effectiveness of such
techniques may be enhanced if combined with the selective
removal of organic bottom sediments by dredging.
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CHEMICAL TREATMENT
Chemicals such as oxidants, flocculants, and non-
wetting agents nay improve dredged materials during or
subsequent to dredging anu disposal operations. Chenical
treatment methods are currently under investigation.
DISP OSAL T REATMEUT
Dredged material may also be treated before being
redeposited. Such treatment would not effect the dredged
site, but could possibly aid in improving the deposition
area.
Suggested methods all of which have had limited
application in treating dredged material before redeposition
include:
Flocculation
Flocculation within a diked disposal area has been
successful in speeding the natural sedimentation process and
thus clarifying the resultant effluent. However, this
technique requires fairly quiescent water, maximum settling
prior to addition of chemicals, and efficient mixing. A
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suggested open water disposal practice would utilize a silt
Carrier to enclose a "treatment area" in which dredged
material could be deposited.
After an initial settling period flocculants would be
applied. j.'his nethod holds promise of limiting possible
undesirable effects of dredged material disposal.
Incineration
Much as in municipal and industrial waste treatment,
the treatment of highly organic dredged material requires
aandling of a solid and liquid phase. Incineration is a
proven technique that can be expected to handle organic
solids and may be applicable to highly organic dredged
material. Sludge with a sufficiently high volatile solids
content occurs in a number of harbor areas. The sludqe
would require preliminary dewatering through settlina,
vacuum filtration, or some other technique before
incineration. Other proposed stabilization techniques
include wet oxidation and fluid bed incineration. Air
pollution must be controlled in all cases.
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Filtration
Tne use of filters of various types is a possibility.
If the spoil contains a sufficient percentage of sand,
gravel, or other large particles, a screening or centrifuge
process can perform fairly efficient water-solids
separation. In the case of finer materials, sand bed
filters, as used in municipal water treatment plants, could
possibly find application in effluent treatnent. Such
filters could be built as integral parts of a diked area.
Since the spoil placed in a confined disnosal area nav
often be physically similar to domestic sewage sludge, the
use of vacuum filters for initial dewaterinrr appears
possible. In this manner, the sludge could be separated out
for eventual inland disposal (by other means such as rail or
road haul). The disposal area could be regarded as a
treatment plant, the larger solids being separated by vacuum
filters and the liquid effluent being treated by other
processes. Pretreatment by coagulant aids such as long-
chain polymers, or alum, would probably be necessary to aid
the dewatering process.
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Sewage 'I'reatnent Plants
Disposal of highly organic dredged material from
waterways into a waste water treatment plant may be
practical in some cases, but is expensive and requires long
periods of time to dispose of large quantities of solids.
The nature and volume of the material would normally
overwhelm the capacity of a typical treatment facility. A
major limitation of this system is the requirement that
dredging operations cease during periods of high sewage
flow, such as those following a rainstorm. The scheme would
L»e unworkable in large dredging projects, but may be a
viable alternative in small projects, particularly if
temporary storage facilities are available to hold the
material for further processing.
uredged Material Disposal techniques
Dreugeu material can be disposed of on land, in
estuaries or in open water. Some of the adverse effects can
oe mitigated or ameliorated by proper disposal site
selection to minimize ecological effects. Additionally,
modified uredging techniques or the use of peripheral
equipment designed to reduce spoil losses can also reduce
adverse effects.
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OPEN WATER DISPOSAL
The Environmental Protection Agency has published
guidelines for disposal in the oceans (16 Hay 1973 Federal
Register) and will establish guidelines for the navigable
waters under Section 404 of Public Lav; 92-500. The
discussion here is of a general nature and not meant to
supplant these activities. Short-terra effects of open water
disposal of dredged material on the benthic biological
community included destruction of less mobile forms whereas
some types were able to surface and survive. High turbidity
associated with spoil disposal apparently had little direct
effect on organism mortality.
Methods designed to minimize the effects of dredged
material disposal include: investigation of current
dispersal patterns before site selection, benthic connunity
surveys and the accurate placement of dredge spoil.
If the spoil contains pollutants, estimates of the
impact of oxygen demands created or the release of toxic
compounds must be made before disposal. Site selection or
the use of alternative disposal methods will be influenced
by the nature and presence of these pollutants.
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LAND DISPOSAL
Land disposal is defined as disposal neither in open
water nor on marsh land. It includes disposal on unland
areas or on bars or islands. Such areas may be confined by
dikes or natural barriers or may be unconfined. Confined
areas are usually equipped with spillways or overflow weirs
and occasionally with settling basins.
Dikes nay be constructed of incompetent material and in
these instances careful design is required to prevent
failure. Dikes have breeched on nunerous occasions causing
extensive losses of spoil. In some instances dikes nay be
pervious and permit seepage through and beneath the
structure. Ground water contamination adjacent to and
jjeneath the disposal area may occur. If such contanination
is likely, the use of liners or other innervious materials
may be required.
Methods of improvement and utilization have been
developed to minimize the effects of dredged material
disposal. The spoil often contains a significant percentage
of fine grained organic constituents and high water content.
Such materials are generally ill-suited for foundations.
Improvement of structural properties can be accomplished by
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uewatering and compacting. Dredged material drains very
slowly because the dikes foster perched water tables and
water retention.
Several methods have been incorporated into projects to
improve the structural properties of the material:
Ditching - The water table can be lowered by ditches which
also provide drainage of surface runoff. Removal of the
water also promotes consolidation.
Sana Drains - i'he vertical sand drain is a cylindrical
column of sand or granular material placed in a vertical
aole and connected at the original surface with a drainage
Blanket. Tnese drains provide an avenue of escape for pore
water and promote consolidation.
Ground Surface urains - This method requires that the
disposal site be initially covered bv a layer of sand before
applying dredged material. The Horizontal sand "blanket"
provides a permanent drain for overlyinq water and promotes
consolidation.
Experimental projects have suggested the possible use
of vacuum wells, electroosmosis and dessication for
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dewatering dredged material. Additional research and
testing will be required to evaluate these technirmes.
MARSHLAND DISPOSAL
Marshlanu disposal has been common in the past because
of accessibility and the inexpensive value of the land.
Because of the increasing expense of other land resulting
from development of coastal areas, these marshlands were
frequently the only land disposal sites available.
Disposal of dredged material on narshes and wetlands is
contrary to existing Enviroilmental Protection Agency policy.
Tne Environmental Protection Agency's policy statement on
protection of the Nation's wetlands appeared in the Federal
Register, Volume 38, Number 84 Wednesday, May 2, 1973. The
policy statement is aimed at preservation and protection of
the wetland ecosystems from destruction by waste water or
nonpoint source discharges. ^he policy makes specific
reference to the necessity "...to protect wetlands from
aaverse dredging or filling practices..."
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Productive Uses of r
Rather than being considered detrimental, spoil can be
used advantageously under certain circumstances.
Potentially oeneficial uses are outlined below.
ARTIFICIAL WILDLIFi: uAblVAV CRUA'x'IOiJ
Among the most promising artificial habitat creation
schemes using dredged material is the dredqed-naterial
island and the creation of marshes. Artificiallv created
dredged-material islands may ue naturally colonised b"
indigenous terrestrial vegetation or specialized waterfowl
feed plants can be introduced. Small lakes nav be created
for fish and wildlife habitats within the disposal area.
Careful spoil placement and recolonization of marsh
vegetation is required. Since many of the nation's marshes
have been destroyed by previous dredging operations and
other of man's activities, the creation of new marshes in
such areas is desirable to restore or replace the ecolocrical
nursery and habitat for fish and wildlife.
Another possible artificial habitat is the development
of shellfish beds in open coastal water areas. Whole
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ecosystem habitats can possibly be re-createu in conjunction
with ureciged material islands and artificial marshlands.
Taese methods must be evaluated as to their possible effect
on existing ecosystems.
1AIJD
Lanu environments adjacent to the oceans, estuaries and
major streams offer valuable sites for commercial,
industrial anu recreational developrient. Dredged material
disposal practices in these areas can be very useful if
properly managed.
Oredgeu material landfill can be directed to the
development of recreational areas to the benefit of man.
Tiie use of life-supporting "top" material on a spoil fill
will encourage rapid development of terrestrial vegetation.
Land created by dredge material disposal has
historically been used in harbor development and for other
construction whether deliberately placed or fortuitously
located. Piers, access roads and commercial and industrial
structures have been constructed on dredged spoil material.
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Special materials such as sand which have good drainage
and competent structural properties should be used where
construction is anticipated. Since these materials are
generally not polluted to a significant dearee, the drainage
and runoff ordinarily cause minimal environnental effects.
iiowever, these projects generally do not assist in the
disposal of material from maintenance dredging which may
contain a uign percentage of silts and clays. Treatment
methods would be required to use these materials in fills
where construction is anticipated.
The use of maintenance dredging materials, often
organically polluted, also creates the possibility of ground
water pollution. Unless the material is appronrlately
treated or the drainage adequately controlled, percolating
waters may convey leached pollutants frori the fill into the
underlying ground waters.
AGRICULTURAL LAUD USL
Isolated studies have been made on the application of
organically rich dredged material to agricultural lands
using methodology similar to that developed for applying
sewage sludge to the land. Careful material selection is
required so that damage may be avoided. Application of
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clay-silt dredged material to sandy soils nay ir.iprove
woisture holding, ion exchange, and textural
characteristics. Inproper application could reduce
drainability.
Agricultural use of marine dredged material generallv
is not possible inasnuch as the high salinity level or the
material may be lethal to plant life. Also, leachinrr of
marine material may seriously impair ground v/ater quality.
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References
1. uoyd, II.i3., R.rj.'. Saucier, J.W. Keeley, R.L. Montgomery,
il.Li. Brown, J.Ii. Matuis and G.J. Guice, "disposal of.
Dredge Spoil, Problem luontification and Assessment and
Research Program Jevelopment,« Teciinical Report H-72-8,
U.S. Arr.y i-nqineer Waten-/ays Lxperirient Station,
Vicksburg, Ilississipni (uovenber, 1972).
2. Saila, S.ii., S.J. Pratt, and T.V. Polgan, "Proviuence
uarbor Iraprovenent Spoil Disposal Site Evaluation
Study, Phase II," university of Rhode Island, Kingston,
Rhode Island (May, 1971).
3. Pierce, ii.u., "Inland Lake Jredqing Evaluation^"
Technical oulletin i^o. 46, Departnent of Natural
Resources, State of Wisconsin (1970).
4. O'iJeal, G. and J. Sceva, "Viie Effects of Jredqing on
Water Quality in the Northwest," U.S. Environmental
Protection Agency, Office of Water Proqrams, Region X,
Seattle, Washington (July, 1971).
»US GOVERNMENT PRINTING OFFICE 1975 546-112 '143
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