South Lake De Cade Freshwater Introduction (TE-39)

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The project area is experiencing marsh deterioration due to subsidence, rapid tidal exchange, and human-induced hydrologic changes that result in increased salinities. Saltwater intrusion has caused a shift in marsh type and a conversion of over 30 percent of emergent vegetation to open water habitat. Shoreline erosion along the south embankment of Lake De Cade threatens to breach the hydrologic barrier between the lake and interior marshes.

Proposed project components include installing three control structures along the south rim of the lake and enlarging Lapeyrouse Canal to allow the controlled diversion of Atchafalaya River water, nutrients, and sediments south into project area marshes. Outfall management structures are planned in the marsh interior to provide better distribution of river water. In addition, approximately 1.6 miles of foreshore rock dike is planned to protect the critical areas of the south lake shoreline from breaching.

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The project is located in Terrebonne Parish, approximately 15 miles southwest of Houma, Louisiana.

After initial engineering investigation, the project was divided into two construction units. Construction unit one consisted of the shoreline protection only and was completed in July 2011. Construction unit two consisting of the freshwater introduction component was further investigated and due to uncertainty of benefits was not constructed, and therefore, the project is considered completed.

This project is on Priority Project List 9.

The Federal Sponsor is NRCS

The Local Sponsor is CPRA

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Salt Water Intrusion

When it comes to Louisiana, there is no one reason for coastal land loss. Causes are both natural and man-made, but when those forces combine, they are detrimental to Louisiana’s coast. One example contributing to these synergistic forces is known as salt water intrusion.

Facts about Salt Water Intrusion: [4]

  • May occur in freshwater systems like aquifers or coastal marshes.
  • Is the movement of saltwater into interior areas or underground sources such as aquifers of freshwater marsh.
  • Most common in coastal regions, where freshwater is displaced by the inland movement of saltwater from the ocean.
  • Can also occur inland, far away from an ocean, as freshwater is pumped out from underground reservoirs and the salt-laden water from surrounding salty layers of the earth flow in.
  • Most common cause of saltwater intrusion is the pumping of freshwater from wells near coasts.
  • Climate change can increase saltwater encroachment along coastal regions as sea level rises.
  • Increased salinity of coastal freshwater can threaten the plant life and wildlife of coastal areas, destroy habitats such as marshes, and force the abandonment of drinking-water supplies.

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Coastal Louisiana is currently experiencing higher than expected salinity in traditionally freshwater marshes, waterways, and reservoirs [1]. It is possible for wildlife to adapt to locally saline conditions, but that is a process that requires time. A study by two professors at the University of Louisiana at Lafayette concluded:

  • Resident marsh fishes have genetic adaptations for localized salinity conditions [1].
  • Continued adaptation will be most successful if salinity increases gradually [1].
  • The existence of adaptation to salinity tolerance will be most important in aiding survival during surges of high salinity, such as those associated with hurricanes [1].

At the same time that sea level is rising, man-made actions are intensifying salt water intrusion through [4]:

  • Canal dredging, including oil and gas access canals
  • Channelization or straightening of natural waterways
  • Construction of levees for flood control
  • General development activities in the coastal zone

CWPPRA hydrologic restoration projects help reduce the inland march of salt water. Culverts and pumps restore the flow of freshwater into marshes, while locks and weirs create “one-way” channels out of the marsh that salt water can’t access.

Sources:

[1] Leberg, P. and Klerks, P. 2004. Final Report: Saltwater Intrusion On The Gulf Coast: An Assessment Of The Interactions Of Salinity Stress, Genetic Diversity And Population Characteristics Of Fish Inhabiting Coastal Marshes. University of Louisiana at Lafayette (ULL). Available: https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.highlight/abstract/5385 [May 22, 2018].

[2] Spatafora, James. 2008. Saltwater Intrusion of Coastal Aquifers in the U.S. Available: http://kanat.jsc.vsc.edu/student/spatafora/default.htm#homepage  [May 22, 2018].

[3] Encyclopedia.com. 2018. Available: https://www.encyclopedia.com/environment/energy-government-and-defense-magazines/saltwater-intrusion [May 22, 2018].

[4] Southern Regional Water Program. 2018. Louisiana Environmental Restoration. Available: http://srwqis.tamu.edu/louisiana/program-information/louisiana-target-themes/watershed-restoration/ [May 22, 2018].

[5] Fowler, Kristen. “Saltwater Intrusion – EnvS 546 Univ of Idaho”. ” 23 April 2016. Online video clip. YouTube. Accessed on 24 May 2018. <http://www.youtube.com/watch?v=puSkP3uym5k>

[6] PBS Newshour. “Testing the limits of saltwater intrusion”. 17 September 2015. Online video clip. Youtube. Accessed on 24 May 2018. https://www.youtube.com/watch?v=75CoHNQVbY8

[7] LSU AgCenter Video Archive. “Saltwater intrusion threatens rice acres”. 8 Jan 2016. Online video clip. Youtube. Accessed on 24 May 2018. https://www.youtube.com/watch?v=Z4TGPtq4bD0

[8] Stanford Alumni. Rosemary Knight, “Sentinel Geophysics: Imaging Saltwater Intrusion from Monterey to Santa Cruz”. 2 April 2014. Online video clip. Youtube. Accessed on 24 May 2018. https://www.youtube.com/watch?v=k4XcBx7OT3Y

 

 

 

South Grand Chenier Marsh Creation – Baker Tract

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Marshes within the Hog Bayou Watershed mapping unit are
stressed due to limited freshwater input and seasonal salinity
spikes exacerbated by construction of the Mermentau Ship
Channel. Other contributors to land loss in the area are
subsidence, compaction, and erosion of organic soils.
Currently, the project area is characterized as large, open
water with degraded areas of wetland vegetation and low
organic production. The dredging of the Mermentau Ship
Channel increased tidal amplitude and salt water intrusion
into the watershed.

The goal of the project is to create new wetland habitat,
restore degraded marsh, and reduce wave erosion of organic
soils. The project would promote the expansion of emergent
marsh and submerged aquatic vegetation throughout the
project area. Material dredged from the Gulf of Mexico will
be used to create and nourish approximately 420 acres of
marsh. Smooth cordgrass will be planted throughout the
area. To help facilitate estuarine fisheries access, constructed
retention levees will be degraded and approximately 11,756
linear feet of tidal creeks will be constructed.

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The project is located in planning Region 4, Mermentau
Basin in Cameron Parish within the Hog Bayou Watershed
Coast 2050 Mapping Unit. The mapping unit is bordered by
Lower Mud Lake to the west, the Gulf of Mexico to the
south, Rockefeller Refuge to the east, and Louisiana
Highway 82 to the north.

This project is on Priority Project List (PPL) 23.

The South Grand Chenier Marsh Creation – Baker Tract sponsors include:

 

Sabine Refuge Marsh Creation Cycle II

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The project area is experiencing marsh degradation due to
saltwater intrusion and freshwater loss. This has resulted
in the conversion of vegetated intermediate marsh to large
shallow open water areas. Salinity migrates into the region
from the Calcasieu River. Southeast winds push saline
waters into the project area through canals and bayous.
Wind driven waves cause further loss of the remaining marsh
fringe.

A permanent dredged material disposal pipeline, measuring
3.57 miles in length, will be constructed in Cycle II. The
pipeline will commence near Mile 13.2 of the Calcasieu
River Ship Channel and terminate at the northeastern corner
of the Sabine National Wildlife Refuge. Much of the right
of way required for the pipeline was previously impacted
by the construction of a temporary pipeline used during the
construction of Cycle I. The pipeline is to be used for future
marsh creation projects in conjunction with the U.S. Army
Corps of Engineers maintenance dredging of the Calcasieu
River Ship Channel.

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The project is located on the
Sabine National Wildlife Refuge, west of Highway 27, in
large open water areas northeast of Brown’s Lake.

The Sabine Refuge Marsh Creation Project was originally
approved as part of the Project Priority List 8 in 1999. The
project was later broken into 5 cycles. In 2004, additional
funds for engineering and design and construction were
approved for Cycle II. The pipeline is constructed and will
be available for use during the 2011 maintenance dredging of
the Calcasieu River Ship Channel.

This project is on Priority Project List 8.

The Sabine Refuge Marsh Creation Cycle II’s sponsors include:

Freshwater Wetlands

Freshwater habitats come in many forms ranging from glaciers to lakes, rivers, and wetlands. These freshwater ecosystems represent less than one percent of the planet’s surface while supporting over 100,000 species including but not limited to fish, frogs, worms, crawfish, and birds and mammals nesting and feeding in wetland vegetation. While serving as habitat for a large number of animals, freshwater wetlands are also home to a variety of plant types. Cattails are a common sight around freshwater lakes and marshes and help in maintaining a healthy ecosystem by filtering runoff as it flows into lakes and serving as a protectant against shoreline erosion. Floating plants, such as duckweed, are a favorite food for many ducks and geese that populate the area.

Freshwater wetlands may stay wet year-round or evaporate during the dry season. Freshwater habitats are some of the most endangered habitats in the world. Human development, agriculture, and pollution are leading factors that put the availability of freshwater at risk. Saltwater intrusion is another underlying factor interrupting the natural conditions of water quality. These impacts have extreme consequences for our freshwater biodiversity, economy, and our well-being. Louisiana’s freshwater wetlands along the coast and other areas are disappearing at a high rate. The Coastal Wetlands Planning, Protection, and Restoration Act implements projects in an effort to preserve freshwater ecosystems.