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YEA 2022 – Fish Bayou Control Structure:  Bluff Swamp & Spanish Lake Flood Risk Reduction Improvements

YEA 2022 – Fish Bayou Control Structure:  Bluff Swamp & Spanish Lake Flood Risk Reduction Improvements

McKim & Creed Inc.

Project Location: Ascension Parish, Louisiana

Category: Water + Stormwater + Wastewater

Started: August 17, 2021

Completed: September 27, 2022

Project Team: 

Kimberly Koehl, P.E., 

Glenn G. Shaheen P.E.

Nicolas Schexnayder, E.I.

Seth Thibodeaux, Engineer Tech.

Mark Maher, Construction Admin.

Tim Dantin, Sr. RPR

Project Summary: The purpose of the project was to provide flood protection & reduce flood duration of the Bluff Swamp by restoring the conveyance of Fish Bayou into Bayou Manchac with the construction of (2) 12’x12′ RCB control structures controlled by SCADA. The Fish Bayou Channel was obstructed by the construction of Alligator Bayou Road and this project restores the channel conveyance system.  Alligator Bayou Road was constructed by the Louisiana DPW in the 1950s and currently acts like a levee, shielding high water in Bayou Manchac from the Bluff Swamp and Spanish Lake drainage basins. This 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 in order to prevent back water flooding from Manchac during high water events and to allow for conveyance of flow from  the swamp once high-water levels in Bayou Manchac reside. This area had inadequate infrastructure which prevented the Bluff Swamp from efficiently draining during high water events in the basin and caused the area to remain inundated until flood waters outfall through the existing 60” 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.

Under the operating plan, the new box culverts will remain open during low water events and close once Bayou Manchac reaches elevation 4.0’ and 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. This new infrastructure will reduce flood risk for Ascension Parish residents and minimize erosion in Bayou Manchac by utilizing rip rap to moderate flows. The rock armoring is used as shoreline protection and to direct 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 benefit to the wetlands within Bluff Swamp. Project was completed on time and on budget.