A new technology — known as the Numerical Fish SurrogateTM — can aid the design of fish bypasses and guidance structures at hydro facilities by combining three types of modeling to forecast fish behavior and trajectories.
All eight hydroelectric projects on the lower Snake and Columbia rivers in the Pacific Northwest feature bypass facilities that divert outmigrating salmon and steelhead away from the turbines and spillbays. Data from Snake River hydro projects indicate bypass system survival (95.3 to 99.4 percent) is generally comparable to that of spillbays (92.7 to 100 percent with flow deflectors and 98.4 to 100 percent without) and greater than that of turbines (86.5 to 93.4 percent).1 Bypass systems are of keen interest because they can reduce both spill and passageinduced mortality. However, to date most bypass systems have achieved only limited and variable success.2,3 The key to good bypass design lies in understanding and forecasting a fish’s response to the hydraulic (and sometimes water quality) conditions it encounters as it approaches a dam.4 To this end, we developed a “plug-and-play” or “hypothesis testing” simulation tool, called the Numerical Fish SurrogateTM (NFS). The NFS integrates fish cognition and perception of hydraulic patterns; particle tracking; and computational fluid dynamics (CFD) modeling to accurately decode and forecast fish behavior and trajectories. To match the movement and passage patterns of observed fish, the NFS uses small-scale individual movements of virtual fish responding to cues from a simulated flow field. The NFS then can be used to forecast the performance of alternative bypass and guidance strategies, as well as to describe the responses of fish to alternative project operations.