National Dam Safety Program. Gaines Mill Dam (Inventory Number VA08506), James River Basin, Hanover County, Virginia. Phase I Inspection report.

Gaines Mill Dam is an earthfill embankment 14.2 feet high and approximately 305 feet long. The dam, located in Hanover County, Virginia, is used to impound water for recreational purposes. Gaines Mill Dam is a small size - high hazard dam as defined by the Recommended Guidelines for Safety Inspection of Dams. The dam and appurtenant structures were in good condition at the time of the inspection. Signs of instability were not observed and a stability check of the dam is not required. The spillway is a concrete broad-crested weir, 25.8 feet long, with the elevation of the crest 2.2 feet below the minimum top of dam and located adjacent to the right abutment. Using the Corps of Engineers' screening criteria for initial review of spillway adequacy, the 1/2 Probable Maximum Flood (1/2 PMF) was selected as the spillway design flood (SDF). The spillway is capable of passing up to 14 percent of the SDF or 7 percent of the PMF without overtopping the dam. Overtopping flows are considered to be detrimental to the embankment. Therefore, the spillway is adjudged as seriously inadequate since dam failure from overtopping would significantly increase the hazard to loss of life downstream from the dam over that which would exist just before overtopping failure.