Scour channel development after spillway failure

Hydraulic structure failure such as the failure of the spillway of a dam may afford the opportunity to evaluate the impacts of this type of event on the formation and migration of a scour channel upstream of the spillway. Such an event occurred in November 1985 at the Lake Charleston dam in Illinois. A portion of the spillway failed during a moderate flood event, and the resulting concentrated flow developed a scour hole ("sinkhole") which migrated upstream until its movement was halted by a rock ledge. The bed elevation of this scour channel was much lower than the original lake bed. Field data on velocity distribution, bed material characteristics, stream gradient, and stream cross sections were collected to evaluate this hydraulic phenomenon. These data and existing streamflow and sediment rating information were used to simulate the development of the scour channel. The HEC-6 model was found to simulate this event quite satisfactorily. Analyses such as this can be a valuable tool in evaluating natural disasters such as the sudden failure of overflow structures along a waterway.