Fowl River marsh spits were slowly succumbing to outside stressors including sea level rise, subsidencce and erosion from boat wakes. The Mobile Bay Estuary Program tasked the ESA/Thompson/Fish-Tec Team with design, permitting and construction of the marsh restoration project. Thin-layer placement (TLP) of dredge material was chosen as a substitute for the sediment that would naturally flow down river and fall out of suspension on the spits. This tactic has been used successfully in marshes nationwide to maintain marsh elevations to combat sea-level rise and subsidence. The thin-layer placement of sediment followed the existing contours of each spit, preserving the natural changes in topography. The thin-layer placement approach increases the overall elevation of the marsh without totally eliminating existing vegetation. Based on future sea-level projections and the monitoring of project success, a second thin-layer placement event was required as "advanced nourishment" to keep pace with sea-level rise.

Thin-layer placement was accomplished through both wet and dry methods from a barge or pump adjacent to the spit. The dry thin-layer placement method utilized a conveyor on a barge to propel the fill material into place. The advantage of this method is far less water is required and therefore little to no decant water to filter and monitor. Some areas required multiple passes to acheive the desired fill placement thickness of 8".

Wet placement combined a cutter-suction dredge which fluidized material from a support barge and pumps the slurry of material to the desired placement site via flexible pipelines and is dispersed through a nozzle into the final placement location. Temporary containment and dewatering was successfully accomplished utilizing hay bales and coir logs.

The sediment was beneficially reused from USACE's Blakely Dredge Material Containment Area (DMCA).  Samples from Blakely were compared to the Fowl River Geotechnical Report, to match the light brown, fine to medium grained sand with 10-15% fines and 10-20% organics found on the marsh spits. The material was trucked to the USACE loading area in the Port of Mobile and then transported by barge to Fowl River and each designated marsh spit. The design process identified approximately 42,000 cubic yards were required to cover the spits with 6-8 inches of thin-layer placement.

The project incorporates an adaptive management approach, monitoring before, during and after each lift of material to inform the best location, thickness and placement methodology.