Director

Turbid, or murky, waters containing sediment have been depositing and developing into a delta complex within Big Mar. With the hope of better understanding the effect of future sediment diversions, we track the expansion and consolidation of this delta. We are beginning to expand these investigations outside of Big Mar and into the larger receiving basin, including any influence the diversion may have on the Breton Sound Basin. To us, new land means more barriers between coastal communities and storm surge! And we can help ensure the longevity and stability of newly formed land by restoring the healthy swamp that once thrived there. That in itself is an intricate task, but luckily for us, the forming delta provides an outdoor laboratory, perfect for identifying best practices for swamp regeneration. We plant species native to swamp environments, and continue to keep tabs on them in the following years, monitoring closely for survival and growth rates to inform future restoration projects. Since 2010, we have planted 25,594 trees and have restored more than 130 acres within Caernarvon receiving basin.

Located 15 miles downriver from New Orleans in Plaquemines Parish near the Plaquemines/St. Bernard Parish line is the Caernarvon Freshwater Diversion.  Constructed in 1991, the diversion was designed to divert up to 8,000 cubic feet per second, approximately the volume of 2,353 large crawfish pots each second. It's intended purpose was to move fresh river water from the Mississippi into the local estuary, limiting the capture of sediment. Despite this, new land is building in the diversion's main catch basin, Big Mar Pond.

Although the diversion was not meant to transport sediment, the subsequent growth of land as a result of its opening resembles the activity of a sediment diversion. For that reason, understanding the effects of the Caernarvon Diversion on the surrounding basin may better inform the construction and operation of future diversions; an integral part of coastal restoration plans for the Southeast Louisiana.

Investigating this emerging delta also offers an opportunity to observe and analyze land building processes as the result of a diversion. It is important to remember that a thriving delta with a restored swamp enhances hurricane storm surge protection to nearby levees and communities (see Multiple Lines of Defense Strategy.)

Caernarvon Freshwater Diversion and Delta

Although LPBF has been active in coastal restoration since its inception in 1989, it was in June 2005 that a formal program was created. This aggressive commitment to the coast was triggered by the realization that the coastal wetlands were getting worse in spite of ongoing authorized restoration programs. A plan was devised by LPBF called the <a href="http://saveourlake.org/lpbf-programs/coastal/multiple-lines-of-defense-strategy/" target="_blank" style="background-color:transparent;color:rgb(66, 139, 202);">Multiple Lines of Defense Strategy</a>. This strategy recognizes natural and manmade lines of defense combined with wetland habitat restoration to provide hurricane protection as well as coastal restoration. Following the hurricanes of 2005, LPBF looked carefully to its <a href="https://saveourlake.org/wp-content/uploads/download-manager-files/chmp-full-report.pdf" target="_blank" style="background-color:transparent;color:rgb(66, 139, 202);">Comprehensive Habitat Management Plan</a>. The CHMP consists of over 100 projects and is the blueprint for restoration of the habitats in the Pontchartrain Basin. The CHMP projects were prioritized choosing the 10 habitat restoration projects that would also provide flood protection for the Greater New Orleans area. These projects became known as the <a href="http://saveourlake.org/lpbf-programs/coastal/pontchartrain-coastal-lines-of-defense-program/" target="_blank" style="background-color:transparent;color:rgb(66, 139, 202);">Pontchartrain Coastal Lines of Defense Program</a>. The Coastal Sustainability Program conducts many <a href="http://saveourlake.org/lpbf-programs/coastal/coastal-projects/" target="_blank" style="background-color:transparent;color:rgb(66, 139, 202);">projects</a> around the basin, including scientific studies, restoration projects and long-term analysis. The development of our <a href="http://saveourlake.org/lpbf-programs/coastal/hydrocoast-maps/" target="_blank" style="background-color:transparent;color:rgb(66, 139, 202);">Hydrocoast Maps</a> provides a bi-weekly snapshot of conditions across the basin. Additionally, LPBF partners with many agencies, NGOs and universities to study, plan and implement projects that protect all of our citizens from future storms and to keep our coastal region economically and culturally sustainable for the future. Scroll down to link to learn more about our Coastal Restoration Projects.

By the 1700’s the Mississippi River had shifted paths back and forth several times - spreading sediment and creating land at the end of an ever-changing delta. The Pontchartrain Basin stretches out into the Gulf of Mexico as a 10,000 square mile watershed from the Mississippi River to the Pearl River and includes 16 Louisiana Parishes and 4 Mississippi Counties.

The construction of levees along the Mississippi River prior to the 1927 flood prevented communities from being flooded but also cut off the nutrients, freshwater and sediment that nourished our wetlands. During the 1927 flood, it became clear that the levees alone were not enough to protect communities and outlets were needed along the river relieve flood waters. During the flood, the levees were breached at Caernarvon and flood waters lowered near New Orleans. The realization that relief outlets were need prompted the construction of the Bonnet Carré Spillway in the 1930's.

In the 1930’s logging of cypress trees in the coastal swamps for their valuable wood resulted in saltwater intrusion from the logging canals (and later the oil and gas canals) which prevented new cypress from growing. This and the introduction of the invasive nutria (Myocastor coypus), which feed on young cypress, prevented natural swamp regeneration. Ultimately the loss of the cypress destroyed the buffer against storms that the coastal swamps provided the urban areas.

In the 1940’s nutria, an invasive species of rodent brought in from South America, added to the coastal woes. A voracious eater of wetland vegetation roots, the nutria has annihilated miles of protective marshland.

As the century continued, oil and gas became prominent economic drivers and critical resources for our nation.  Access to these was provided by navigation canals and pipelines which crisscrossed South Louisiana marshes.  Unfortunately, in the process, the coastal marshes were lost when spoil banks were left randomly throughout the area, disastrously altering the natural hydrology of the region.  The canals caused saltwater intrusion and more land was lost.

Looking back through the 20th Century, to a large degree, the reduced coastal hurricane protection for South Louisiana was the result of poor decisions made in the 1900’s.

Historically, Bayou St. John drained water off the natural crescent-shaped bank of the Mississippi River to Lake Pontchartrain. The connections between Bayou St. John, the Lake and the River were essential in the founding of New Orleans. In 1699, native guides showed French explorer d’Iberville the waterway they called ‘Bayouk Choupic’ (mudfish) by the Acolapissa Indians and now called Bayou St. John. With its mouth at Lake Pontchartrain, the bayou ran for 5 miles through an ancient cypress swamp and connected to the Mississippi Rive by a 1-mile portage. Vessels traveled along the Mississippi coast to enter Lake Pontchartrain, to Bayou St. John and to the very bank of the Mississippi River where New Orleans was founded in 1718 at the French Quarter.Most local commerce in the 1700’s and 1800’s was not on the Mississippi River but through the Bayou St. John “back door” to the Isle of Orleans. It was Bayou St. John and Lake Pontchartrain that made New Orleans possible for its first century.During the past century, New Orleans sprawled away from the river’s high ground into surrounding wetlands, transforming the bayou and its swamp into an urban landscape. In the 1920’s, a portion of the lake was filled, extending the mouth of the bayou into what was open water. Levees were built on this reclaimed shoreline and enclose most of Bayou St. John.As use of the bayou changed and residential development along the bayou persisted, water flow management from Lake Pontchartrain to the bayou became an essential task. In 1962, a flood control structure was built at Robert E. Lee Boulevard to replace a 1930’s lock. In the late 1970’s and early 1980’s the Orleans Levee Board, responsible for Lake Pontchartrain area hurricane protection, began discussions about closing the mouth of the bayou entirely in order to abandon the need to enhance the levees lining the bayou. The public, supported by neighborhood groups and elected officials, fought to instead implement alternative flood control methods resulting in construction of a new flood control structure near the mouth of the bayou. In 1982, Bayou St. John was designated by the Louisiana Legislature as a “Historic and Scenic River”, which “requires protection and preservation of its aesthetic, scenic, recreation, fish, wildlife, ecological, archaeological, botanical and other natural and physical features.” Currently, the nearby flood gates are operable, however, due to land subsidence, the bayou is lower than the lake so the gates can now only be opened for brief periods or else the surrounding neighborhoods would be flooded.In 2013, the Orleans Levee District dredged a channel through a sand bar that had closed off the mouth of Bayou St John from Lake Pontchartrain. The goal was to increase water flow into the bayou when floodgates are opened, part of a long term effort to improve the bayou’s water quality. LPBF saw an opportunity to beneficially use dredge material to create wetland habitat.The project needed creative solutions for sediment containment in a high-energy environment. LPBF partnered with EMS Green of Belle Chasse, LA to build retaining walls of geotextile sandbags locked together with spiked plastic “Deltalok” plates. 7,400 bags containing 185 tons of sand were filled and moved by hand to create 560’ of dike in 2’ to 3’ of water, using over 1,000 volunteer hours. Sandy mud was dredged from the middle of the bayou and placed behind the retaining walls, which proved stable enough to hold over 2,000 cubic yards of fill. The “soft armoring” stabilized the final elevation as the fill material settled.In 2014, after proper settling time of the newly placed sediment, the wetland was planted. Over 5,000 plugs of 8 native grass and sedge species were planted by volunteers. Many of the plants were planted into <a href="http://www.ekosystemspartners.org/pdf/REF.GSS.SpartinaCost.analysis.commercial.pdf" target="_blank" style="color:Black;">Gulf Saver bags</a>, biodegradable bags with a custom mixed supply of nutrients in order to jump start plant growth. The Gulf Saver bags were provided our partners at the <a href="http://www.restoretheearth.org/" target="_blank" style="color:Black;">Restore the Earth Foundation</a>. Most of the grasses that were planted were smooth cord grass or <a href="http://plants.usda.gov/core/profile?symbol=SPAL" target="_blank" style="color:Black;">Spartina alterniflora</a>. Other plants included saltmeadow cordgrass (<a href="http://plants.usda.gov/core/profile?symbol=SPPA" target="_blank" style="color:Black;">Spartina patens</a>), bullrush (<a href="http://plants.usda.gov/core/profile?symbol=SCCA11" target="_blank" style="color:Black;">Schoenoplectus californicus</a>), common rush (<a href="http://plants.usda.gov/core/profile?symbol=JUEF" target="_blank" style="color:Black;">Juncus effusus</a>), dwarf spike-rush (<a href="http://plants.usda.gov/core/profile?symbol=ELPA5" target="_blank" style="color:Black;">Eleocharis parvula</a>), giant cutgrass (<a href="http://plants.usda.gov/core/profile?symbol=ZIMI" target="_blank" style="color:Black;">Zizaniopsis miliacea</a>), common three square (<a href="http://plants.usda.gov/core/profile?symbol=SCPU10" target="_blank" style="color:Black;">Schoenoplectus pungens</a>), and roseau cane (<a href="http://plants.usda.gov/core/profile?symbol=PHAU7" target="_blank" style="color:Black;">Phragmites australis</a>).Scientific monitoring is an essential part of any restoration project, in order to be able to assess successes and failures, rate of change and to gain lessons learned. Monitoring helps to adaptively manage projects if needed and also helps to make future projects of the same type more successful by applying lessons learned forward. At the Bayou St. John Urban Marsh, a monitoring program was set track the changes in vegetation and soil over time. Since mostly only one species of plant was planted we expect diversity to increase over time. Also, after the planting, there was still a lot of bare ground which we would expect plants to fill in over time. The dredge material that was placed was very sandy. We would expect the soils to become more organic over time as wetland plants decomposed and roots spread. The monitoring program tracks these changes over time.The monitoring revealed that many freshwater annual and perennial plants colonized the wetland on their own but the plants that were planted remained dominant after three years. Total percent cover did not get as high as expected, most likely due high water levels causing extended inundation. Overall, the wetland creation project has been successful so far, and has maintained and flourished in it's first three years. More details about the monitoring results can be found in our report <a href="http://saveourlake.org/download/bsjum-report_2017/?wpdmdl=12616" target="_blank" style="color:Black;">"Bayou St. John Urban Marsh: Summary of construction and 2014 to 2017 monitoring."</a>

The Bayou St. John Urban Marsh is part of a larger project to improve the health of Bayou St. John. Restoration to the historical condition is impossible due to urbanization along the banks of the bayou. At the mouth of the bayou the channel was dredged in order to increase flow into the bayou when the flood gates are opened. By having natural wetlands close to the opening, it is intended to encourage organisms to use and live in the wetland and then when the gates are opened, the organisms are swept into the bayou. By introducing the fresh, oxygenated water and small organisms that are the basis of the food chain, the health of the bayou will be improved. Water from the bayou is pumped into City park and becomes part of the lagoon system.

BAYOU ST. JOHN URBAN MARSH

Studying the Bohemia Spillway offers an opportunity to observe natural processes at work. Before levees were built, during flood events, the river would overtop the natural levee of the Mississippi River and water would spill into the adjacent forests and wetlands. While current conditions of the river (maximum discharge, sediment load) and the receiving basin (presence of canals and trenasses) have changed over time, the Bohemia Spillway still offers a glimpse into the past of the way the river may have operated before human intervention. It also offers a glimpse at the historical interaction between the river and the wetlands before the river levees were built. The spillway also allows us to see the effects of pulsed overbank flow on wetlands which may inform future operation of river diversions.LPBF has been investigating the spillway since 2007 and in this time was able to study the effects of the floods of 2008 and 2011. In 2010 a survey was conducted of the Bohemia Road that runs the length of the spillway along the natural levee. This allowed us to determine (for the most part) the controlling elevation for overtopping along the length of the spillway. In other words, the elevation of the natural levee (in most cases the road) would be the elevation the river would need to top for the spillway to flow water. During the flood of 2011, we conducted and extensive hydrologic survey of the spillway. The findings from this survey can be found our report entitled “<a href="https://saveourlake.org/wp-content/uploads/download-manager-files/our-coast/Bohemia/Bohemia%20Report_March2013.pdf" target="_blank" style="color:Black;">Bohemia Spillway in southeastern Louisiana: History, general description, and 2011 hydrologic surveys</a>.” In addition to the hydrology of the spillway, we also conducted a geomorphic analysis and 2010 vegetation survey. Additionally we used a novel technique to closely analyze the land loss and land gain in the spillway over time.It was discovered during the 2011 Mississippi River flood survey that overtopping waters were captured quickly by small natural channels, trenasses and gullies shortly after the water overtopped the natural levee. Little overland flow was observed, relegated to the forest found along the natural levee and not reaching the adjacent marshes.It was also discovered through our land loss analysis from 1932 to 2010 that there have been low land loss rates in the spillway since 1975. Most of the land loss that occurred before 1975 is from the dredging of oil and gas and navigation canals and borrow pits. The Bohemia Spillway does not seem to suffer the same interior land loss due to subsidence as other parts of the coast. This stability may be the result of periodic pulses of water received from the Mississippi River during flood events but could also be due to underlying geology, or a combination of the two.During our extensive surveys, we also observed navigation and oil and gas canals infilling, which is a rare site in southern Louisiana. The presence of man-made canals usually enhances erosion through of saltwater intrusion, increase in wave energy and directing storm surge farther inland.The vegetation survey revealed that the patterns at the Bohemia Spillway are what to be expected given the environment. The narrow swath of forest present along the Mississippi River resides on the natural river levee and is therefore at a slightly higher elevation than the adjacent marsh. The elevation, as one moves away from the river, drops quickly and the landscape quickly grades into a narrow band of scrub/shrub and then into expansive marshes. The species composition in the brackish and salt marshes is typical of these environments in Louisiana.Through our observations and study, we have concluded that the pulsed flow from the Mississippi River in flood years since 1926 has contributed to the sustainability and resiliency of marshes in the Bohemia Spillway.

The Bohemia Spillway is located in Plaquemines Parish on the east bank of the Mississippi River about 35 miles southeast of New Orleans, LA. In the 1920’s Mississippi River stages at New Orleans were becoming higher and more threatening, and so the Bohemia Spillway was authorized in 1924 by the Louisiana State legislature for the purpose of creating a river flood relief outlet and reducing flood risk to New Orleans.  The Bohemia Spillway was completed in the Fall of 1926 by the Orleans Levee District with the removal of the artificial Mississippi River levees, and remarkably just two months before the onset of the Great Flood of 1927. The spillway has a broad elevated river bank (natural levee) that slopes gently to the marsh and to Breton Sound. Since 1926, the natural levee of the Bohemia Spillway has been periodically overtopped during flood events on the Mississippi River.

BOHEMIA SPILLWAY

Turbid, or murky, waters containing sediment have been depositing and developing into a delta complex within Big Mar. With the hope of better understanding the effect of future sediment diversions, we track the expansion and consolidation of this delta. We are beginning to expand these investigations outside of Big Mar and into the larger receiving basin, including any influence the diversion may have on the Breton Sound Basin. To us, new land means more barriers between coastal communities and storm surge! And we can help ensure the longevity and stability of newly formed land by restoring the healthy swamp that once thrived there. That in itself is an intricate task, but luckily for us, the forming delta provides an outdoor laboratory, perfect for identifying best practices for swamp regeneration. We plant species native to swamp environments, and continue to keep tabs on them in the following years, monitoring closely for survival and growth rates to inform future restoration projects. Since 2010, we have planted 25,594 trees and have restored more than 130 acres within Caernarvon receiving basin.

Historically, prior to European settlement, the Central Wetlands was made up of a combination of bald cypress (Taxodium distichum) and water tupelo (Nyssa aquatica) swamp, fresh marsh and bottomland hardwood forest. This provided natural storm surge protection for the people of New Orleans.  The Central Wetlands have been subjected to many anthropogenic and natural impacts over time including, leveeing of the Mississippi, construction of oil, gas, and navigation canals, construction of the MRGO, the construction of the levees around the Central Wetlands and logging. Currently, the Central Wetlands are a mosaic of wetland habitats that range from relatively healthy with stable soil and dense vegetation to open water and ghost swamps. They are subject to influences inside and outside the area that can have an effect on hydrology and salinity dynamics.

There has been great interest and much conversation about the restoration and effective management of the Central Wetlands since Hurricane Katrina devastated much of the Ninth Ward community and surrounding area. The closure of the MRGO was a solid first step towards hydrologic restoration. Currently, there are several restoration plans and pilot projects in consideration that would impact the Central Wetlands and attempt to restore some of the natural habitat while strengthening ecosystem services. These plans and proposals include, but are not limited to: marsh creation, cypress‐tupelo and marsh plantings, and wastewater assimilation. The success of planting projects depends largely on the suitability of the planting location, namely soil salinity and hydrological conditions, to the vegetation being planted. An in-depth understanding of the environmental parameters found across the Central Wetlands will allow for more informed planning of restoration activities, which will increase the success and effectiveness of those restoration activities and their impact on the surrounding communities.

Our Coast

Caernarvon Freshwater Diversion and Delta

Introduction

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Backstory and Context