National Dam Safety Program Potashnick Lake Dam Mo 30565 Mississippi St Francis River Basin Wayne County Missouri Phase 1 Inspection Report PDF Download

This report assesses the general condition of the dam with respect to safety, based on available data and on visual inspection, to determine if the dam poses hazards to human life or property. Evaluation of the spillways' size indicates that they do not meet the criteria in the guidelines. The spillways of dams No. 2 and 3 are of inadequate size to pass the one percent chance flood (100-year flood) without overtopping. The spillway of dam No. 1 is just adequate to pass the one percent chance flood; but if either dam No. 2 or No. 3 failed due to overtopping, dam No. 1 would overtop also. The inspection team observed trees and bushes growing in the three dams inspected, particularly dam No. 3. These root systems are a potential seepage hazard. Localized areas of the embankment slopes are exceptionally steep. Steady seepage conditions exist through dam No. 1 and a localized seepage area was found downstream of dam No. 2. The pool of the dam No. 2 was on the downstream slope of dam No. 3 and seepage could not be evaluated. The three spillways do not appear sufficiently resistant to prevent embankment erosion at high flows for an indefinite time. Stilling basins are needed below each spillway. Seepage and stability analyses are not on record as recommended in the guidelines.