National Dam Safety Program. Butterfly Lake Dam (MO 30501) and Rainbow Lake Dam (MO 30641), Mississippi - Kaskaskia - St. Louis Basin, Ste. Genevieve County, Missouri. Phase I Inspection Report

摘要

Inspection and evaluation indicate that the outlet facilities of Butterfly and Rainbow Lakes do not meet the criteria set forth in the guidelines for dams having the above size and hazard potential. Butterfly Dam is an intermediate size dam with a high hazard potential required by the guidelines to pass the PMF. It was determined that the outlet facilities will pass 20 percent of the PMF without overtopping the dam. Rainbow Dam is a small size dam with a high hazard potential required by the guidelines to pass from one-half PMF to the PMF. However, considering the high hazard potential to life (four families) and property downstream of the dam, the outlet facilities should be able to pass the PMF without overtopping the dam. It was determined that the outlet facilities will pass 15 percent of the PMF without overtopping the dam. The outlet facilities of Butterfly Dam will pass the 100-year flood without overtopping the dam. Rainbow Dam outlet facilities will not pass the 100-year flood. The 100-year flood is defined as a flood that has a 1 percent chance of being equalled or exceeded during any given year. Since the outlet facilities for the Butterfly Lake and Rainbow Lake Dams are not capable of passing a minimum of one-half (50 percent) of the PMF without overtopping the dam and causing failure, the outlet facilities are considered seriously inadequate and the dams are accordingly classified unsafe, non-emergency structures.