Physical Hydraulic Model Study of Impacts of Spillway Debris
May 1, 2025 • Webex
We are pleased to announce that we have scheduled a webinar regarding “Physical Hydraulic Model Study of Impacts of Spillway Debris” on Thursday May 1st at 1pmET, presented by Melissa Shinbein of U.S. Bureau of Reclamation.About the Presentation:Recent events such as Rapidan Dam have highlighted the need to better understand the risk debris can pose on dam infrastructure. Reclamation has performed physical hydraulic model testing on multiple configurations including radial-gate and morning-glory spillways. These tests aimed to determine the impacts of reservoir woody debris on the water surface elevation (WSE) behind a dam and the discharge capacity of the spillway structure with the goal of incorporating these findings into risk assessments. Debris jams were formed by steadily introducing woody debris into a reservoir and allowing the jam to form with natural physical processes as the flow approached and passed the spillway structure. Testing included two main methods, referred to as individual log testing and simulated flood routing. Individual log testing kept the inflow at equilibrium throughout the test. Simulated flood routing tests raised and then lowered inflows in fixed time increments to simulate an inflow hydrograph. For the morning-glory spillways, debris impacts on discharge capacity were greatest during weir flow, with up to a 52% reduction. Once the flow regime progressed to pipe control, debris impacts were reduced because buoyancy kept the debris pieces at the surface of the reservoir. Debris presents a significant risk to morning glory spillways regardless of pier configuration by significantly reducing the discharge capacity. For the radial-gated spillways, at small gate opening relative to reservoir head woody debris impacts were minimal and at times produced a more efficient spillway structure. At large gate opening relative to reservoir head, the maximum impacts produced a prototype WSE rise of 4.5-feet and a discharge capacity reduction of 50%. However, radial gated spillways can present a unique operational opportunity if there is not a critical minimum reservoir WSE. Therefore, even if debris impacts are significant, operational flexibility can be maintained.