Pontchartrain Levee District needed assistance with flood risk reduction, specifically minimizing flood duration within the Bluff Swamp. McKim & Creed’s team helped accomplish this by restoring the conveyance of Fish Bayou into Bayou Manchac with the construction of two 12×12-foot reinforced concrete box (RCB) gated control structures controlled by SCADA.
The Fish Bayou Channel was obstructed by the construction of Alligator Bayou Road by the Louisiana Department of Public Works in the 1950s. Alligator Bayou Road mimics a levee, shielding high water in Bayou Manchac from the Bluff Swamp and Spanish Lake drainage basins and vice versa. This project restores the Fish Bayou Channel conveyance system and reduces flood risk for Ascension and Iberville Parish residents.
The leveeing of the natural flooding process has also resulted in negative impacts to the wetlands within Bluff Swamp. Sluice gates were installed on the box culverts to prevent backwater flooding from Manchac during high water events and to allow for conveyance of flooding conditions of the swamp once high-water levels in Bayou Manchac reside.
The area suffered from inadequate infrastructure which prevented the Bluff Swamp from efficiently draining during high water events and caused the area to remain inundated until flood waters drained through the existing 60-inch drainage structure at Frog Bayou. Due to the previous structure size limitations, the Bluff Swamp sub-basins remained inundated for a period of two months during the August 2016 flood event.
With the new plan in place, the control structures were designed to remain open during low water events and will close once Bayou Manchac reaches an elevation of four feet and is increasing. This protects both Iberville and Ascension Parishes from backwater flooding along Bayou Manchac. The gates will remain closed until the waters along Bayou Manchac reduce enough to create a head differential which promotes drainage of Bluff Swamp and Spanish Lake.
In addition to reducing flood risk, this new infrastructure will minimize erosion in Bayou Manchac by utilizing rip rap to moderate flows. The rock armoring is used as shoreline protection and directs the flow of Fish Bayou into Bayou Manchac. A weir was constructed upstream of the structure within Bluff Swamp so that water will remain in the swamp continuously which has ecological benefits to the wetlands within Bluff Swamp.
In September 2022, Pontchartrain Levee District hosted a ribbon-cutting ceremony for the Fish Bayou Channel.