Bayou St. John Urban Marsh
Bayou St. John Urban Marsh
Bayou St. John Urban Marsh
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.
1875 map showing the original New Orleans settlement and Carondelet Canal, built in 1794 to allow boats to traverse from Lake Pontchartrain down the Bayou St. John and Canal to the French Quarter.
Bayou St. John Urban Marsh Creation Project
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. PC saw an opportunity to beneficially use dredge material to create wetland habitat.
Marsh creation plan before construction showing the new dredged channel, marsh creation sites with tidal channels and the flood gate.
Engineering plan and specifications for the marsh creation project.
The project needed creative solutions for sediment containment in a high-energy environment. PC 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.
Construction of Deltalok retaining walls using volunteer labor. Spiked plates were placed in between the layers of sandbags to increase wall strength.
East wall completed. Also channel dredging is beginning in the background. The dredge material was placed behind the wall to create the urban marsh.
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 Gulf Saver bags, biodegradable bags with a custom mixed supply of nutrients in order to jump start plant growth. Most of the grasses that were planted were smooth cord grass or Spartina alterniflora. Other plants included saltmeadow cordgrass (Spartina patens), bullrush (Schoenoplectus californicus), common rush (Juncus effusus), dwarf spike-rush (Eleocharis parvula), giant cutgrass (Zizaniopsis miliacea), common three square (Schoenoplectus pungens), and roseau cane (Phragmites australis).
Volunteers planting Spartina alterniflora at Bayou St. John site. Some Spartina alterniflora was planted in Gulf Saver bags. The bags were buried slightly before planting so they would stay in place during high water events.
Bayou St. John Urban Marsh 2 months after planting.
Bayou St. John Urban Marsh Monitoring
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.
One meter square quadrats were used to assess the vegetation at 42 sites in the created marsh. All live vegetation within each quadrat was identified to species and % cover of each species was determined. The total live vegetative cover in each quadrat was also determined. Soil cores were collected at all 42 plots and analyzed for bulk density (a measure of soil compaction) and % organic matter. The elevation of each of the 42 plots was also measured using a high precision GPS. This allowed for the tracking of elevation changes over time with potential settling, erosion, or deposition.
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 "Bayou St. John Urban Marsh Monitoring Report 2014-2019."
Improving the Health of Bayou St. John
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.
Water from Bayou St. John is pumped into City Park where it becomes part of the lagoon system. Since many people fish in the lagoons, good water quality in Bayou St. John needs to be maintained.
Dredging the channel allows more flow to enter the bayou when the sector gates are opened. The created marsh nearby provides a home for organisms at the base of the food chain which are swept into the bayou when the gates are open. This provides a food source for larger animals that live in the bayou.
Visit the Flourishing Bayou St. John Urban Marsh!
The Bayou St. John Urban Marsh is a success, with vegetation flourishing and animals rapidly moving in. Anglers have noted increased fish numbers and diversity, and shorebirds, waders and ducks are feeding in the new habitat. It is a living classroom and a laboratory for restoration, and puts regional problems in a local perspective: the half-acre marsh is the area lost every half hour in south Louisiana. The urban oasis provides a place for citizens to fish, relax, and recreate.
Please email info@ScienceForOurCoast.org for Directions to Bayou St. John Urban Marsh
Resources
Email info@ScienceForOurCoast.org to obtain archived (no hyperlink) files.
Bayou St. John Fact Sheet
Bayou St. John Comprehensive Management Plan
Bayou St. John Marsh Creation Project
Bayou St. John Urban Marsh Monitoring 2014-2019