As part of the Savannah Harbor Expansion Project mitigation efforts, the U.S. Army Corps of Engineers (USACE), Savannah District selected Tetra Tech to design the largest rock arch weir fish passage in the United States. The fish passage will replace the deauthorized New Savannah Bluff Lock and Dam, maintain the upstream recreation pool, and allow endangered sturgeon to reach critical spawning habitat for the first time in 90 years.

Tetra Tech’s fish passage design spans the entire width of the Savannah River and includes a floodplain bench. The fish passage was designed to allow a variety of fish species, specifically Atlantic and shortnose sturgeon, reach the Augusta Shoals upstream spawning grounds. Tetra Tech’s hydraulic design and modeling team worked with the National Oceanic and Atmospheric Administration, the U.S. Fish and Wildlife Service, and USACE to create a fish passage that meets required minimum depths and maximum velocities for fish movement through the rock weirs.

Our team utilized the Hydrologic Engineering Centers River Analysis System (HEC-RAS) 2D model and computational fluid dynamic modeling software to optimize the fish passage crest height, floodplain bench dimensions, fish resting pool dimensions, and rock boulder placement. The HEC-RAS model allowed Tetra Tech designers to set the crest and floodplain bench height so required minimum upstream water surface elevations were met, ensuring municipal water withdrawals would have access to needed flow and that water elevations would not increase upstream flooding. Using the computational fluid dynamic model results, our team modified the rock boulders arrangements to meet proper velocities for the range of flows in the Savannah River. The sinuous rock weir arches of the structure maximize the number and size of resting pools, providing plenty of resting locations for migrating fish, as well as areas that may potentially be used for spawning fish species like robust redhorse.

In addition to the design, Tetra Tech performed geotechnical explorations and subsurface environmental assessments on land and in water. Tetra Tech also conducted the laboratory soil testing, seepage, and stability analyses on the geotechnical borings to confirm that the excavated soils in the floodplain bench may be used for in-river fill material, which could save money during construction.