Session A4- Use of a 2D model for fish passage design and for informing management and user groups

Step pool ramps, often referred to as rock ramp weirs, are a commonly employed technique for restoring fish passage at towhead dams In the Midwest United States. Hydraulic design typically employs 1D modeling (e.g., HEC RAS) to simulate water surface elevations, water depth, and average velocity conditions. Flow depth and velocity are hydraulic parameters typically used to design and evaluate fish passage projects but lD models simulate these variables as cross-sectional averages. Two dimensional hydrodynamic modeling w-as added to lD modeling for the design of a rock ramp ·weir fish passage project at the Evans-Tonn irrigation diversion on Spearfish Creek, Spearfish, SD. The numerical mesh was refined in areas of greatest interest and model calibration relied on water surface elevations and depth-averaged velocity measurements collected at GPS referenced locations. A range of flow regimes and irrigation diversion scenarios were evaluated during the fish passage design. The 2D model added sediment transport design capability, enhanced fish passage design, and provided enhanced diversion-scenario evaluation capabilities. Additionally, the 2D model coupled with the pre and post processing Surface Water Modeling Software (SMS) provided a visual tool that public administrators, lay public, and irrigation proponents could use to evaluate various designs and operation scenarios. We suggest that 2D modeling will become a standard for fish passage design as its utility and acquaintance with fish passage designers increases