Aquia Dam Raise and Rehabilitation - A Team Success Story

Stafford County is located in northern Virginia about 40 miles south of Washington, DC. Municipal water supply is provided to the County by two surface reservoirs owned and operated by the Department of Utilities. One of these is the 3,000 acre-foot, Smith Lake reservoir which borders the Quantico Marine Base. Smith Lake was created by the construction of a dam on the Aquia Creek in 1969. Aquia Dam is an earth embankment structure, 1,600 feet long with a maximum height of 65 feet. The crest of the dam is at Elevation (El) 90 with a normal pool of El 70. The principal spillway consisted of a concrete, rectangular drop inlet with a 60-inch reinforced concrete pipe (RCP) extending from the riser to the downstream toe and discharging into Aquia Creek. The emergency spillway consisted of a 160-feet wide broad crested weir and a concrete lined chute at the left abutment. Because of potential downstream impacts to Route I-95 and several communities, Aquia Darn was classified by the State as a Class I high hazard structure requiring an inflow design flood equivalent to the Probable Maximum Flood (PMF) due to downstream impacts from a potential dambreak. Studies conducted in the 1980s concluded that the existing dam and spillways could manage only 19°/0 of the PMF and the State directed the County to increase the capacity of the emergency spillway in order to manage the fill PMF, Due to unprecedented growth, the County decided to combine the goals of public safety and increasing water supply capacity. A 1990 preliminary study indicated that the dam could be safely raised by 20 feet to provide an additional site yield of about 3 million gallons per day (MGD). This study focused on the use of a labyrinth spillway to increase the spillway capacity to the fill PMF. In 1993, the County decided to proceed with design of the modifications to Aquia Dam and Smith Lake. 11 pp.