Spillway Debris Physical Model Study: Morning-glory Spillway Structure

Physical hydraulic model tests were performed on two different configurations of a morning glory spillway (with and without piers) 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. 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. For both configurations, debris impacts on discharge capacity were greatest during weir flow, with up to a 52 percent 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, especially when under weir control.