National Dam Safety Program. Rainbow Lake Dam (MO 30544), Upper Mississippi - Kaskaskia - St. Louis Basin, Franklin County, Missouri. Phase I Inspection Report

摘要

Based on the visual inspection and the results of the hydrologic/hydraulic investigations, the present general condition of the dam is considered to be less than satisfactory. Deficiencies were noticed during the inspection and are considered to have an adverse effect on the overall safety and future operation of the dam. Seepage, as characterized by cattails, willow trees, soft ground, and standing water was observed in two areas adjacent to the toe of the downstream slope of the dam. Uncontrolled seepage could develop into a piping condition (progressive internal erosion) that can lead to failure of the dam. Erosion of the grass covered upstream face of the dam apparently by wave action and/or fluctuations of the lake surface level has created a near vertical bank approximately 12-to-18 inches high. A grass covered slope is not considered adequate protection to prevent erosion of the embankment by wave action or fluctuations of the lake level. Loss of material by erosion can be detrimental to the dam's stability. At the time of the inspection, the grass and other turf cover on the dam slopes was about 3 feet high. Some areas of the dam were also covered with undergrowth including small tress and dense brush. The vegetative cover should not be allowed to reach a height that provides cover for burrowing animals or hinders inspection of the dam.