Physical hydraulic debris modelling to aid decision making for flood overtopping

Between 2017 and 2019, the US Bureau of Reclamation’s Dam Safety Office funded a physical hydraulic model to study reservoir debris and spillway structure interaction, to quantify the impact that debris can make to reservoir outflows. The initial model was based on a generalized gated ogee-crest spillway geometry. It was designed to have a broad application across the Bureau of Reclamation’s portfolio of dams and resulted in a water surface elevation increase of up to 1.4 m, and a discharge reduction of 50 per cent for a debris jam formed during steady-state equilibrium conditions. A conservative upper limit to debris impacts was created by manually compacting the debris jam, and this resulted in up to 2.6 m water surface elevation increase and a discharge reduction of 85 per cent in the prototype model test.