Guidelines for Dam Breach Analysis and Hazard Classification in Colorado

Since the mid to late 1980s, engineers and meteorologists have posed serious questions about the uncertainty regarding the magnitude of extreme precipitation that can occur at high elevations in the Rocky Mountain region. Many federal and state agencies use extreme precipitation estimates, or probable maximum precipitation values, to derive the inflow design flood for determining a spillway’s hydraulic capacity. Overly conservative estimations can lead to unnecessary spillway upgrades and have a significant economic impact on the owner of a dam. In 1989, the Dam Safety Branch of the Colorado State Engineer’s Office recognized this concern and placed a moratorium on the hydrologic review of existing dams located above 7,500 feet until further research could be conducted. The Branch contracted with Colorado State University's Department of Atmospheric Science to conduct a comprehensive effort to better understand extreme precipitation as a function of location and elevation. The Branch developed its guidelines for breach analysis and hazard classification as a first step in resuming hydrologic review of existing dams located above 7500 ft. 10 pp., 11 references.