Dam Safety Assurance Study Dorena Lake Row River Oregon

The Tygart Dam probable maximum precipitation (PMF) was reviewed by a Dam Safety Assurance Study and found to be hydraulically deficient. During the PMF, overtopping flows will flow down the back side of the dam and scour foundation material from the toe of the dam. The resulting loss of stability will cause failure of the dam because of the sliding or overturning of one or more monoliths. Tygart Dam was reproduced in a 1:60-scale physical model to study ways of handling the overtopping flow. The model and testing conditions were reproduced according to prototype data received from the U.S. Army Engineer District, Pittsburgh. Experiments conducted on the structure showed that the overtopping flow can be routed into the stilling basin and prevent scour. This is accomplished by constructing gutter channels on the back side of the dam at ground level. Experiments also showed that the existing stilling basin and downstream channel can adequately handle the increased discharge.