Mechanics of an Earth Spillway Failure

ABSTRACT Severe storms in Mississippi during May of 1983 produced flooding that resulted in one of the few flood control reservoir auxiliary spillway failures on record. Subsequent analysis of the breach using state of the art procedures reproduced the downstream observations of high water, but failed to reproduce the observed timing of the failure or conditions observed at the site during spillway operation and failure. The present effort uses the observed failure conditions, site geology, and a simplified model of failure mechanics to develop an independent estimate of the breach outflow hydrograph. Agreement with the previously estimated peak discharge is surprisingly good. The analysis, although site specific, clearly demonstrates the important role of surface and soil discontinuities in the failure process.