Physical Modeling and CFD Modeling of the South Fork Tolt Spillway

The South Fork Tolt Project is owned and operated jointly by two departments of the City of Seattle: Seattle Public Utilities (SPU) and Seattle City Light (SCL). The Sixth FERC Part 12 inspection report (2017) and a subsequent spillway focused evaluation report (2020) identified recommendations to study and evaluate potential improvements at the SF Tolt Spillway. Kleinschmidt was engaged to identify and evaluate these improvements using advanced hydraulic modeling studies to inform spillway wall overtopping and access bridge impingement due to shock waves. A 1:18 scale physical model (Bureau of Reclamation) and a 3D CFD model (RIE Consultants) were used to define the hydraulic characteristics of the spillway, including depth, velocity, shockwaves, pressures, and cavitation index. Kleinschmidt used the results of the hydraulic modeling to inform development of improvement options and to support selection of a preferred option to address dam safety considerations and water supply resiliency.