Moving Land: Erosion and Sediments

Land loss and land gain are terms we throw around a lot at CWPPRA but what do they mean? Where does the old land go and where does the new land come from? To answer that, we need to understand that “land” is made of inorganic particles that we call sediment and various types of organic matter. Sand, clay, gravel, boulders, and silt are all types of sediment, and grain size is how we classify them. [1] For example, a boulder is larger than gravel, which is larger than a grain of sand, which is larger than a silt particle, etc. Sediment size influences how each grain experiences force and inertia, which leads to different rates of land loss and gain between sediments. Imagine holding a handful of sand in one hand and a handful of gravel in the other. Now imagine you blow as hard as you can on each one. More gravel would stay in your hand than sand. The same is true of sediment in water- smaller grains of sand can be picked up more easily by the forces acting on them than the gravel can.

Erosion detaches sediment from an original source, such as a cliff face or the middle of a valley. Over long periods of time, eroded particles get smaller and smaller, eventually degrading to sand or silt, depending on the mineral base. Once they get into a river or stream, their movement is connected to water flow. When water flows faster or stronger, it “suspends” and carries more sediment, while sediments in slower currents tend to settle out and “deposit” on the bottom of the lake, bayou, or swamp. Approximately 40% of the USA drains through the Mississippi River, and any suspended sediment in those waterways travels through Louisiana on its way to the Gulf of Mexico. [2]

Sediments move downstream differently depending on their size class.

Wetlands are defined by sediment type and other characteristics including salinity. In Louisiana, we have fresh water wetlands like swamps and bottomland hardwood forests, but also saline wetlands like salt and brackish marsh. Each of these wetlands types contains fine sediment particles, and they are all relatively new in the scope of geologic time. Because they are young, there are not many hard-packed substrates in Louisiana wetlands, but instead deeper layers of sediment that are compacting and subsiding. [3] Sediment replenishment is important to all the wetlands in Louisiana because new sediment is needed on top of compacting sediment to maintain elevations that support plant life and productive ecosystems. Unfortunately, sediments that should be replenishing the wetlands of Louisiana are not doing so. Instead, they are being transported out into the Gulf of Mexico or are trapped farther upstream behind dams. More information about this topic can be found in our post “The Mississippi River Deltaic Cycle”. Controlling the flow of the Mississippi river keeps sediments suspended for longer because water does not disperse or slow down as it naturally wants to. Without new sediment, marsh platforms lose structural integrity and they erode, leaving open water where marsh once was.

To answer the original question; for CWPPRA land loss is the process of sediment and marsh sinking or eroding into open water along Louisiana’s coastline and reducing the land available. Land gain describes the process of sediment depositing to form new platforms and it is much less common along our coast, but CWPPRA and their Partners in Restoration are working to restore the integrity of coastal wetlands by moving and capturing sediment, planting stabilizing species on terraces, and creating marsh in critical areas. Combating land loss is a multi-disciplinary effort, and we have a long fight ahead.

 

Featured image: http://amazonwaters.org/waters/river-types/whitewater-rivers/

Embedded image: http://blog.sustainability.colostate.edu/?q=schook

[1] https://www.tulane.edu/~sanelson/eens1110/sedrx.htm

[2] https://www.nps.gov/miss/riverfacts.htm

[3] https://www.sciencedirect.com/science/article/pii/S027277140600312X

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The Watershed Flood Center

On May 4, 2018, the University of Louisiana introduced an important new venture: The Watershed Flood Center. [1] In response to massive flooding in August of 2016 in Southern Louisiana, experts will come together to develop a better understanding of flooding in the area. Torrential downpours hit the state consistently on August 12 and 13 of 2016, amounting to more than 31 inches in Watson, LA, and more than 20 inches in Lafayette, the new home base for the Center. Atmospheric conditions caused a series of storms to form and stay over southern Louisiana for those two days, dropping and estimated 2 inches of water per hour. [2] Across the state, an estimated 7.1 trillion gallons of rain came down on August 12th and 13th, more than three times the volume Louisiana received during Hurricane Katrina in 2005.  The flooding caused an estimated $10-15 billion dollars in damages across the affected parishes, including almost 150,000 homes and businesses. [3] This catastrophe was called a 1-in-1000-year flood because meteorologists attributed a .1% chance to something of this scale happening in any given year based on past events. The Watershed Flood Center seeks to study how much that chance may be increasing with projected changes in atmospheric and climatic conditions.

Basins that will be researched at the new center | Source [1]

Wetlands are adapted to flooded conditions, so they are great for mitigating floodwaters. Mitigation allows water to be stored and released when needed, so they act like a sponge. Unfortunately, the sheer volume of water that came and stayed was too much to redirect into neighboring wetlands. Wetlands used to be more prominent but as towns and cities expand into wetlands, mitigation potential of those wetlands diminishes. Thanks to development and decreased wetland area, much of the flooded area was inundated and impassable for over a week even after the rain had stopped.

The new center at The University of Louisiana at Lafayette is far from the only research venture the university funds. ULL has many research centers and partners, including LUMCON, the Ecology Center, and the Informatics Research Institute, to name a few. These centers study many branches of science, including infectious diseases, immersive technologies, ion beams, and soon the list will include the flood-condition hydrology of Louisiana. The Watershed Flood Center is currently in development and, once completed, will study flood events with real-time monitoring to develop better forecasts to protect public interests. [4]

 

[1] https://thecurrentla.com/2018/a-new-flood-research-center-launched-to-put-fractured-regional-efforts-on-the-same-page/

[2] https://en.wikipedia.org/wiki/2016_Louisiana_floods

[3] https://weather.com/forecast/regional/news/rain-flood-threat-south-mississippi-ohio-valley

[4] https://floodcenter.louisiana.edu/research/projects

Featured image from http://www.theadvocate.com/louisiana_flood_2016/article_dbfba072-7148-11e6-a7b4-0f0b3863c31e.html

Marsh Island Hydrologic Restoration (TV-14)

banner_tv-14.fwReasons to Restore:

  • Natural erosion
  • Subsidence
  • Construction of navigation canals along the northeast shoreline of a Marsh Island.
  • Deterioration of the north rim of Lake Sand and the interior marshes.

Restoration Strategy:

  • Stabilizes the northeastern shoreline of Marsh Island.
  • Stabilizing the northern shoreline of Lake Sand.
  • Help restore the historic hydrology.
  • Construction of 7 closures for oil and gas canals at the northeast end of Marsh Island.
  • Protect the northeast shoreline with rock including the isolation of Lake Sand from Vermilion Bay.

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[2]

Location:

This project is located in Iberia Parish, Louisiana, on the eastern portion of the Russell Sage Foundation Marsh Island State Wildlife Refuge and surrounding Lake Sand.

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Project Effectiveness [1]:

  • Effective at reducing water level variability within the northern portion of the project area
  • Water level variability did not increase in the project area as is did in R1 post-construction
  • Reducing erosion rates at the northeast shoreline was partially met
  • Reduced erosion in areas of applied rock dikes versus unprotected areas.
  • The steel sheet pile, rock rip-rap wingwall, and stone bank paving installed at each end of closure No. 5 proved to be successful in preventing erosion during a storm event.

Previous Progress [2]:

  • The monitoring plan was finalized in January 2000 following with further data collection.
  • Pre-construction and post-construction aerial photography were in the year 2000, and 2009 with future imagery analyses upcoming.
  • Water level, submerged aquatic vegetation and shoreline position and movement data were also collected to evaluate project effectiveness.

Progress to Date [1]:

  • Construction was completed in December 2001.
  • This is one of the three projects nearing the end of their 20 year lives.
  • The Task Force will vote on the Technical Committee’s recommendation on the path forward for the following projects [1]:

3 projects

This project is on Priority Project List (PPL) 6.

Project Sponsors Include:

                     US_AOE_Logo

 

  CPRA_logo_sponsor                

Source:

[1] Mouledous, M. and Broussard, D. 2014. 2014 Operations, Maintenance, and Monitoring Report for Marsh Island Hydrologic Restoration. Coastal Protection and Restoration Authority (CPRA). Available:https://lacoast.gov/ocmc/MailContent.aspx?ID=10092 [May 22,2018].

[2] Marsh Island Hydrologic Restoration (TV-14) Land-Water Classification. 2009. Coastal Wetlands Planning, Protection, and Restoration Act (CWPPRA). Available: https://www.lacoast.gov/products/sab_net_pub_products/map/original/2011-02-0009.pdf [May 22, 2018].

The Mississippi River Deltaic Cycle

Water flows downhill naturally and, over time, will make a river change from one path to another. As sediment moved and elevations changed over the last 7 millennia, the Mississippi River has emptied into several historic delta complexes: Maringouin, Teche, St. Bernard, Lafourche, Plaquemines-Balize, and Atchafalaya. Each of the deltas built up part of Louisiana’s coast to what we see today, but now that natural process has been interrupted [1]. After the great Mississippi flood of 1927 that caused $1 billion worth of damages (almost $1 trillion in today’s dollars), the US Army Corps of Engineers built the world’s longest levee system under the Flood Control Act of 1928. The Levee system was constructed to reduce flood damages and allow for more control of the Mississippi [2].

Image 1: Historic Deltas of the Mississippi River

An unforeseen and unfavorable side effect to taming the river was that all the water is kept moving too quickly to deposit sediment, and now sediment is lost to the Gulf of Mexico rather than deposited into our coastal wetlands [3]. Our Louisiana coastline is dependent on new sediment to nourish wetland ecosystems. Without sediment delivery, there is no material for natural land gain or replenishment, which will continue to contribute to our retreating coastline. The solution is not as simple as removing the levee system, however, since so much of Louisiana is populated now, and removing the levees containing the Mississippi would displace millions of residents from their homes. Instead, CWPPRA and our partners in restoration use man-made systems to create marsh, nourish wetlands, and maintain hydrologic connectivity so that we can protect and restore Louisiana’s coast.

 

 

[1] https://en.wikipedia.org/wiki/Mississippi_River_Delta

[2] https://en.wikipedia.org/wiki/Great_Mississippi_Flood_of_1927

[3] http://mississippiriverdelta.org/our-coastal-crisis/wasted-sediment/

Image 1 from https://www.nationalgeographic.org/photo/miss-delta-formation/

Featured image from https://phys.org/news/2015-04-future-mississippi-delta.html

Prothonotary Warblers

 

As April passes into May, many migratory birds leave the tropics of Central and South America in search of bountiful summer resources in the sub-tropical United States. Among them, the very charismatic Prothonotary Warbler flies from the northern tropics to the hospitable habitats of the United States. Prothonotary warblers live in forests near bodies of slow-moving water where they can hunt for insects and nest in cavities in trees. The cypress swamps of Louisiana are about as good as it gets for a prothonotary warbler, and they stay from April to August. [1] If you get out into the swamp during the summer, look for their bright yellow figures darting through low-lying foliage.

Prothonotary warblers have experienced a population decline in recent years that experts attributed to the destruction of their wintering habitat in the tropics.[2] To improve breeding success and survivorship, the Audubon Society and other ornithological enthusiasts have encouraged people to install nest boxes that help to protect warbler nests from failing. Many natural threats exist in swamps for warblers, including a variety of snakes, birds of prey, and mammals. Since brown-headed cowbirds will use prothonotary nests to lay their eggs in when given the chance, nest boxes are suggested to have a 1¼“ hole to prevent larger birds from entering the box but still allow the warblers to enter. Boxes are not left on the ground, and are often mounted on poles. Some predators can climb, so many boxes have a skirt/collar that prevents snakes, raccoons, and cats from climbing the poles into the nests. More guidelines for a good nest box can be found at https://nestwatch.org/learn/all-about-birdhouses/features-of-a-good-birdhouse/.

 

 

[1] Petit, L. J. (1999). Prothonotary Warbler (Protonotaria citrea), version 2.0. In The Birds of North America (A. F. Poole and F. B. Gill, Editors). Cornell Lab of Ornithology, Ithaca, NY, USA. https://doi.org/10.2173/bna.408

[2] Kaufman, Kenn. “Prothonotary Warbler.” Audubon, National Audubon Society, 10 Mar. 2016, http://www.audubon.org/field-guide/bird/prothonotary-warbler.

Featured Image:

Brannon, Peter. “Adult Male.” All About Birds, The Cornell Lab of Ornithology, Florida, 14 Sept. 2016, http://www.allaboutbirds.org/guide/Prothonotary_Warbler/id.

UL-Lafayette Fête de la Terre

What better way to spend a Friday afternoon than with jambalaya, Cajun music, and conservation? That is how the CWPPRA outreach team and many other organizations spent last Friday, April 20th, at the UL-Lafayette Fête de la Terre Expo. The expo showcased many wonderful local groups including, but not limited to, the Citizens’ Climate Lobby, the TECHE Project, and the Bayou Vermilion District, all hosted by the ULL Office of Sustainability.

Students visiting the expo could learn about how long it takes for different types of litter to decompose naturally, how solar panels are used to generate power, and whether or not to recycle different waste products. During their visit, they could grab free jambalaya, listen to the Cajun jam session, or decorate their very own reusable grocery bag. There are so many resources that help our community celebrate conservation, and the expo was a beautiful day for getting ULL students and faculty involved, interested, and informed.

 

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Black Bayou Culverts Hydrological Restoration (CS-29)

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The marsh within this area has been suffering from excessive water levels within the lakes subbasin that kills vegetation, prevents growth of desirable annual plant species, and contributes to shoreline erosion. Black Bayou offers a unique location in the basin where the water in the lakes subbasin and the outer, tidal waters are separated by only a narrow highway corridor.

Project components include installing ten 10 foot by 10 foot concrete box culverts in Black Bayou at the intersection of Louisiana Highway 384. The structure discharge will be in addition to the discharges provided by Calcasieu Locks, Schooner Bayou, and Catfish Point water control structures.

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The project features are located in southern Calcasieu Parish, Louisiana. The majority of the project area is located east of Calcasieu Lake and includes areas north of the Gulf Intracoastal Waterway and west of Grand Lake in Cameron Parish, Louisiana.

Construction has been completed.

This project is on Priority Project List 9.

Federal Sponsor: NRCS

Local Sponsor: CPRA