For our project area, we chose an open water area that had previously been marsh, and was near the LSU study area so that we could use the benchmark and water level gage they had established. The source for fill material would be the adjacent dead-end canal that had been acting as a sediment trap and was less than 1/3 of its original depth.
We went through the Louisiana Coastal Zone permitting process to permit a 16-acre area to use for our project. The surveys we conducted showed that the target pond depth averaged around a foot from substrate to marsh level, and calculations confirmed that the canal which acted as a sediment trap held enough material to fill it.
Professor Irv Mendelssohn and his research group at the LSU Biogeochemistry Laboratory agreed to monitor and study the marsh restoration process and wanted 5 cells approximately the same size to use as replicates, so they chose the east end of the pond. We set up a test cell to practice and develop our dredging technique toward the west end of the pond so that it wouldn’t affect their site. Each of these cells was about a third of an acre.
To prepare for pumping into the test cell or the study cells, we built a walkway that would hold the pipe off of the marsh surface and prevent the frequent foot traffic from damaging the marsh platform. This also made an excellent platform for documenting changes and observing results.
On November 22, 2010, the dredge was moved to the test site. The 4-inch dredge hose was assembled from the dredge to shore, across the levee, down the walkway and into the test area. The test site was used for Audubon staff (Karen Westphal and Timmy Vincent) to self-train on the dredge and experiment with techniques of dispersing the sediment. We tried free-flow and through a spreader, without containment and then with containment. Without containment or with low water levels, the mud was too fluid to stack and flowed into the larger pond through self-created channels.
The containment chosen for most applications was bundles of roseaucane (Phragites sp) laid in an overlapping fashion and tied between posts cut from tallow trees (Sapium sebiferum) or bamboo. In the Rainey area, any land elevated above marsh is covered by this tall cane, and the bundles are easy to make, carry, stack, transport and tie down, and it is a renewable and almost unlimited nearby resource. It is biodegradable, and a local and native organic addition to the marsh mud. And, it comes free of foreign seeds or chemicals. The tallow trees are also abundantly available along the nearby levees, and are considered an invasive.
The cane containment worked wonderfully. It diffused the flow so there was no main channel and raised the water level slightly. It stopped wind agitation, which allowed the sediment to settle out faster and stopped material from being removed by wave action.At the end of the 11 hours of contained pumping, the cell appeared to be filled to within 2 inches of marsh level.
In our test cell, the land manager transplanted some smooth cordgrass against the containment, to test the idea that they would root and spread by the time the cane degrades, to act as future containment while the marsh establishes itself.
In June 2011, the dredge was moved down to the east end of the pond to start pumping into the LSU study cells. We used the same arrangement of placing the dredge hose along the boardwalk then to the furthest point we could reach to start pumping into Cell 5. Roseaucane bundles were placed to create containment around Cell 5 and the outer boundaries of Cell 4. A sturdier containment was needed for the long reach on the outer boundary of Cell 1, so Timmy and I constructed a plywood wall. We ripped plywood sheets into 2ft x 8ft lengths, then pushed them into the substrate so that there was about 6 inches above marsh level. These were pinned into place using 4ft 2x4s.
Cell 5 was considered “filled” in November 2011, Cell 4 was filled in May 2012, and Cell 3 was filled in August 2013. The dredge worked along the canal, and the discharge hose was shortened in the pond and lengthened and moved along the canal to keep up. Containment was added or removed between cells as it became necessary.
The picture below was taken in April 2012 from an ultralight floatplane. The view is to the northwest, with the outfall (small white square) in Cell 4. Google Earth imagery is available online for April 23: 29°41’57.85″N 92°12’36.93″W.
The same area was photographed in June 2015 (see below).
A graphic map depicting the estimated status of the site was made periodically to document marsh restoration progress. In the Figure below, brown colors are fill above marsh level which is the target elevation, and pink/purple is fill below marsh level. This shows that we lost a good bit of material into the other cells through our leaky containment. The bright green color indicates new vegetation that has either spread by rhizomes from existing marsh stands or colonized by seed. Any substrate within -2 inches of marsh level was quickly accepted by the low marsh, and substrates above +3 inches are colonized by high marsh and wetland herbs.
We were concerned that our pumping activities might adversely affect the diverse wildlife in the area, but they took advantage of the dredging operation instead. Within 30 minutes of shutting off the pump, birds gathered to feast on the minnows and crabs that are pushed into the ¼ inch of clear water above the settling mud. After a day, raccoon, bird and alligator tracks crisscross the new shallow areas. Even around the dredge, with all of the noise from the pump and machinery, the wildlife soon settles back into normal activities. We have alligators and pelicans that feed within 6 feet of us; crabs, shrimp, and juvenile fish are attracted to the bubbles from the pump or feed on the algae on submerged parts; birds build nests and feed babies along the adjacent shore; flocks of birds pass over; and migrating butterflies flit through the uprights. When the water is high, our dredge site may be the only mudflat in the marsh, and it gets crowded with shorebirds.