&EPA
New Options for Dredging in
Barataria-Terre bonne
Demonstrating Practical Tools for Watershed
Management Through the National Estuary Program
Barataria-Terrebonne Basins, Louisiana
Characteristics:
The Problem:
The Barataria-Terrebonne Estuary includes over 4.1 million
acres of wetlands, vvaterbodies. farmlands, and forests in 15
Louisiana parishes. Approximately 602.000 people live and
work w ithin its boundaries. The area contains a multitude
of natural and man-made waterways, providing water
access for industries such as oil and gas production and
shipping.
The wetlands surrounding the estuary are being lost at the
remarkable rate of 21 square miles per year (one half-acre
every 15 minutes). Extensive characterization and
modeling of the Estuary and its wetlands as part of the
Barataria-Terrebonne National Estuary Program has shown
that one of the major causes of wetlands loss has been
human modification of the hydrology of the system through
such actions as construction of navigation canals and
levees.
Thousands of cubic yards of material are dredged
throughout coastal Louisiana every year for the
maintenance of oil and gas canals and navigation channels.
The majority of this material is either prop-washed or
placed on existing levees of dredged material in a manner
not conducive to the propagation and enhancement of
adjacent marsh vegetation.
One of the most common methodologies employed by
public and private entities for displacing dredged material
is the use of bucket dredges, with which sediments are dug
out and placed on the shore adjacent to the water body. The
levees created with this dredged material, sometimes called
"spoil banks", form impoundments or otherwise impede
natural sheet flow hydrology.
The extensive wetland losses appear to be exacerbated by disruptions to
the natural hydrology of the system. Impoundments, produced by dredged
material levees, block water flow over land between marsh and water.
They also disrupt the critical process of sedimentation on the surface of
the marsh from tidal floodins.
The Project:
The purpose of the Alternative Dredging and Spoil Deposition Project
was to determine the costs and benefits, both economic and
environmental, of using a small hydraulic dredge for maintenance of oil
field canals, as opposed to the traditional bucket dredge. The
project was designed to place a thin-layer deposition of
dredged material over the marsh in order to create new
marsh and/or restore habitat and to avoid creating
impoundments.
The National Estuary Program
* istuaries and other coastal and marine waters tire national
r~J resources that are increasingl\ threatened hy pollution, habitat
m, J loss, coastal development, and resource conflicts. Congress
established the National Estuary Program (NEP) in 1987 to provide a
greater focus for coastal protection and to demonstrate practical,
innovative approaches for protecting estuaries and their living resources.
As part of the demonstration role, the NEP offers funding for member
estuaries to design and implement Action Plan Demonstration Projects
that demonstrate innovative approaches to address priority problem
areas, show improvements that can he achieved on a small scale, and help
determine the time and resources needed to apply similar approaches
basin-wide.
The NEP is managed by the U.S. Environmental Protection Agency
(EPAj. It currently includes 28 estuaries: Albemarle-Pamlico Sounds,
NC; Barataria-Terrebonne Estitarine Complex, LA: Barnegat Bay. NJ;
Buzzards Bay, MA: Casco Bay. ME: Charlotte Harbor. FL: Columbia
River. OR and WA: Corpus Christi Bay. TX: Delaware Estuary. DE. NJ.
and PA; Delaware In/and Bavs, DE: Galveston Ba\. TX: Indian River
Lagoon, FL: Long Island Sound, CT and NY: Maryland Coastal Bays.
MD: Massachusetts Bays, MA: Mobile Bay. AL: Morro Bay, CA;
Narragansett Bay, RI; New Hampshire Estuaries, NH: New York-New
Jersey Harbor, NY and NJ: Peconic Bay, NY: Puget Sound, WA: San
Francisco Bay-Delta Estuary, CA: San Juan Ba\. PR: Santa Monica Bay.
CA: Sarasota Buy. FL: Tampa Bay, FL: and Tillamook Bay. OR.
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Introduction to Barataria-Terrebonne
T~lie Barataria-Terrebonne Estuary lies between the Missis-
A. sippi and Atchafalaya Rivers in south central Louisiana. It
is rich beyond imagination in natural resources and cultural
heritage, and provides billions of dollars of revenue to the
region, the State of Louisiana, and the nation through indus-
tries such as commercial fishing, trapping, agriculture,
tourism, shipping, and oil and gas.
Unfortunately, the Barataria-Terrebonne Estuarine System is
facing a serious crisis. This nationally significant area is
experiencing land loss at a faster rate than any other region in
the nation, about 21 square
miles per year. This trans-
lates to about one half-acre
every 15 minutes. Studies
have shown that over
445,000 acres of marsh
converted to open water
between 1932 and 1990, and
conservative estimates are
that an additional 163,000
acres of land will be lost by
the year 2010.
The lowland swamps,
marshes, and low ridges of
Barataria-Terrebonne were
built by accumulating
Mississippi River sediment.
As the river flowed through
the area, it deposited sediment in deltas and during flood
stages, deposited sediments on the surface of the wetlands
themselves. Marsh plants quickly invaded these newly formed
lowlands.
Periodically, the river would change course and find a shorter
pathway to the Gulf. Without the continuing riverine deposits,
soft marsh sediment compacted and the land sank below sea
level. Meanwhile, new land built up along the repositioned
channel. Before human intervention, sinking land in one spot
was replaced with new land somewhere else.
Today, the rivers carry less sediment than a century ago.
Additionally, levees constructed to prevent flooding funnel the
How straight to the Gulf where most of the sediment is lost in
deep water. Consequently, new land is not forming. Addition-
ally, impoundments resulting from dredging activities prevent
sheet flow across the wetlands, precluding sediments from
maintaining existing wetlands.
Over the previous century the Barataria-Terrebonne marshes
have been criss-crossed with channels to accommodate
navigation and the oil and gas industries. In order for these
revenue-generating industries to continue to thrive, waterways
The discharge from the hydraulic dredge pumps a slurry of bottom
sediments onto the face of the marsh.
must be maintained at sufficient widths and depths. This is
typically accomplished through maintenance dredging, most
often done with bucket dredges. The dredged material is
placed on the marsh along the edge of the canal, forming
levees which block the natural sheet flow of water, and
sediments, over the marsh surface. Additionally, the material
covers, and ultimately kills, the existing marsh vegetation.
When they become extensive enough, the levees form
impoundments on the surface of the marsh which prevents
sediments from reaching the marsh surface and maintaining its
elevation. The impoundments can also flood from storm
overwash or rising ground water which leads to standing water
which also will kill marsh
vegetation. This combination
of loss of sediment and
standing water leads to marsh
compaction and loss of
wetlands. Studies have shown
that there is a direct correla-
tion between the existence of
canals, dredged material levee
density, and land loss. Local
erosion is often isolated
around the levees or within
areas partially or wholly
impounded by them. For this
reason, the Barataria-
Terrebonne National Estuary
Program believes that it is
important to promote alterna-
tive techniques that will
beneficially use dredged material to enhance adjacent marsh
areas.
The amount of dredging done within the estuary (over 22
million cubic yards of material have been dredged in
Lafourche Parish alone in the past fifteen years) and the
resulting levees and impoundments make this a significant
aspect of wetland loss.
Overview of the Demonstration Project
/s hydraulic dredging a viable alternative to bucket dredg-
ing? Do the benefits outweigh the costs? Can new marsh be
created by thin-layer deposition of dredged material over
marshes? The Barataria-Terrebonne National Estuary Program
thought so, but wanted to investigate.
Scientists recognize hydraulic dredging as a viable alternative
to bucket dredging. This alternative has fewer detrimental
impacts and is recognized as producing a more beneficial use
of dredged material. Pumping fluidized dredged material over
the marsh, rather than concentrating it in a levee, reduces the
effects and degree of impoundment and in many ways mimics
the natural deposition of sediment from river flooding. The
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hydraulic operation involves pumping dredged material from
canal or channel water bottoms to a nearby containment area.
Containment areas in shallow water require the construction
of a minimal retention levee to hold slurry material until the
water drains or evaporates out of the contained area.
Project Objectives
r j Tie purpose of the Action Plan Demonstration Project was
J. to compare the costs and benefits of using a small
hydraulic dredge for maintenance of an oil field canal and
placement of material in a thin-layer deposition in order to
create new marsh and/or restore habitat.
Implementing the Project
rr*b achieve the project's objectives, Texaco, Inc. and the
A Barataria-Terrebonne National Estuary Program entered
into an agreement with the Lafourche Parish Coastal Zone
Management Program for project design and implementation.
Eight potential sites for deposition of dredged material were
identified in the Leeville field in Lafourche Parish, Louisiana.
The field is highly active with a number of canals and sections
of deteriorating marsh sites. The sites vary in size, depth,
percent of vegetation
coverage, and degree of
impoundment.
Soil investigations found
them td be a "Timbalier-Belle
Pass associate" characterized
by very fluid organic soils
overlying a very fluid clay. A
pre-construction over-flight
provided current aerial
photos of the area. The Parish
subsequently entered into a
professional service contract
with Picciola and Associates,
Inc. for surveying, technical
specifications, advertise-
ments, and administrative
aspects of the project and
contracted with Grillot Company, Inc. to dredge 26,600 cubic
yards of material and deposit it onto four sites.
Before dredging commenced, retention levees were built, as
needed, using a marsh buggy elevator, and monitoring stations
were constructed by the National Biological Service of
Lafayette, LA. The data to be obtained included: thickness of
dredged material after deposition, diversity, compaction of the
material over time, subsidence of pre-dredge pond bottom
over time, subsidence over vegetation vs. subsidence over
pond bottom, and changes of plant diversity/abundance/
biomass over time as related to change in sediment cover.
The dredging itself took eight days to complete. The dredge,
"Crown Point", was 85 feet in length and 24 feet wide and
required a 4.5 foot draft. It had a 42-inch cutter head and
could potentially dredge to a depth of 38 feet and discharge to
a distance of 3,500 feet without a booster station. The dredge
discharged at a 200 yd3/hr. rate through a 12-inch effluent
line.
Success Stories
Although the project was designed to do a cost comparison
of hydraulic vs. bucket dredging, it also provided the
opportunity to study and determine if the environmental
benefits of utilizing the bucket dredge method outweigh the
additional costs. Monitoring of sites was conducted in June
and October of 1996, and the sites were visited in January and
March of 1997. A preliminary analysis of a small portion of
the data collected at three ponds in Leeville, LA provided an
indication of the amount of material accumulated and the
levels of subsidence occurring. This admittedly preliminary
analysis suggested that the deposited material did compact as
expected. The material enhanced the sites and created new
marsh in areas that were formerly covered by water. Existing
vegetation appears to be thriving, and sprouting vegetation is
visible throughout.
The project has shown that
hydraulic dredging is a
viable alternative to bucket
dredging and can be effec-
tive not only in enhancing
existing marsh but also in
creating new marsh.
The Barataria-Terrebonne
National Estuary Program
believes that it is important
to promote the use of
hydraulic and other alterna-
tive dredging techniques that
will beneficially use dredged
material to enhance marsh
areas. Thin layer deposition
is one method that has fewer detrimental impacts than bucket
dredging techniques and reduces the effects and degree of
impoundment. Alternative techniques need to be explored as
well. The costs associated with the dredging work may be
slightly higher, at least initially, but the environmental
benefits outweigh the costs in the eyes of many.
4 year after dredging, new marsh growth ix evident
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Lessons Learned
Although the project's cost comparisons showed that, in this
instance, the hydraulic dredge technique was more expensive
than the bucket dredge method ($1.96 per cubic yard versus $.91 per
cubic yard), several important factors were revealed:
• To date, the use of hydraulic dredge operations in South Louisi-
ana has been infrequent. This factor has two important effects on
the cost of the beneficial use technique—^economists agree that
the lack of competition increases the price and a lack of equip-
ment and experience with small hydraulic dredges in the oil and
gas field contributes to the higher cost. It is predicted that if this
technique becomes more widely used, the per unit cost would
decrease.
• Hydraulic dredging technology may provide opportunities for the
public and private sectors to work together to achieve beneficial
use of dredged material in a coordinated effort that would assist
public goals of wetland creation and coastal restoration. Coopera-
tive agreements can be sought to share costs associated with
hydraulic dredge work.
* Coastal Use Permit applicants could reduce the amount of off-site
mitigation required for habitat damage caused by their dredging
activities by beneficially using the material to restore or create
marsh habitat. In cases where applicants create more wetland
values with dredged material than they alter by dredging, they
would be eligible to receive advanced mitigation requirements for
future projects. Such opportunities would promote cost savings in
mobilization and demobilization by having fewer, larger projects
utilizing equipment already on-hand.
For further information, contact:
Printed on Recycled Paper
Previous Publications in the Demonstration Projects Series
Report Title
Biological Nutrient Removal Project
Buttermilk Bay Coliform Control Project
Georgetown Stormwater Management Project
Texas Coastal Preserves Project
Shell Creek Stormwater Diversion Project
City Island Habitat Restoration Project
Buzzards Bay "SepTrack" Initiative
National Estuary Program Date Publication #
Long Island Sound, CT/NY 1995 EPA842-F-95-001A
Buzzards Bay, MA 1995 EPA842-F-95-001B
Delaware Inland Bays. DE 1995 EPA842-F-95-001C
Galveston Bays, TX 1995 EPA842-F-95-001D
Puget Sound. WA 1995 EPA842-F-95-001E
Sarasota Bay. FL 1995 EPA842-F-95-001F
Buzzards Bay, MA 1997 EPA842-F-97-002G
For copies of any of these publications contact:
National Clearinghouse for Environmental Publications
Telephone: (513)489-8190
Facsimile: (513)489-8695
&EPA
United States
Environmental Protection Agency
(4504F)
Washington, DC 20460
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