HEADCUT ADVANCE PREDICTION FOR EARTH SPILLWAYS

New technology for predicting the performance of earth (sail and rack) spillways has been developed through the joint efforts of the Agricul tural Research Service (ARS) and the Natural Resources Conservation Se rvice (NRCS). This technology has been computer coded, and the resulti ng computational model incorporated into NRCS software. As a part of e valuating the potential for spillway breach, one component of this mod el predicts headcut advance within the spillway This component utilize s an energy-based parameter to describe the erosive attack and a headc ut erodibility index to describe the resistance of the geologic materi als to that attack. Headcut advance threshold and rate parameters were calibrated using data from field spillways that had experienced extre me flow events. The model was validated using data from additional fie ld spillways. Results of the validation suggest that the model should provide a useful tool for current use, but that additional data and mo del refinement are needed.