Recent Rehabilitation Experience with Old Concrete Dams

Abstract Only - During the past two years, GEI has been engaged to design and implement rehabilitation measures for several concrete dams built in North Carolina and Virginia during the 1920's. Each dam had unique concerns that had to be addressed.

Lake Michie Dam in Durham, North Carolina is a 94-foot hight concrete dam that was part of a former hyrdoelectric facility that is now used for water supply. The former hydroelectric plant iis located at the base of the dam and is now used as a pumping station for the city's water supply. Hydrologic analyses performed by GEI for the revised design storm of 1/2 PMP indicated that the dam would be overtopped and the water discharge plant would be flooded and damaged. GEI designed a parapet wall to increase spillway capacity and also designed measures to repair spillway channel damage caused by Hurricane Fran.

Reddies River Dam in Borth Wilkesboro, North Carolina is a 25-foot high concrete dam that was also part of a former hydroelectric facility. The dam now impounds a run-of-the-river reservior that is the sole source of water supply for the Town. Boarded-up sluiceways at the base of the dam started to leak and jeopardize the Town's water supply. If the reservoir level dropped to two feet below the top of the dam, the intake pumps would lose their prime and water could not be pumped into the distribution system. GEI designed and implemented measures to seal the sluiceways under full reservoir level and provide a new low-level outlet during the process. GEI is currently designing a new gate for the former penstock.

GEI and Dewberry & Davis of Fairfax, VA were engaged by the Town of Big Stone Gap, Virginia to design post-tensioned anchors to improve the stability of Big Cherry Dam. This dam impounds the sole source of water supply for the Town. GEI performed a field investigation that included coring through the dam and into the bedrock foundation. The coring revelaed that the dam was constructed with cyclopean concrete that is now in poor condition. Due to the poor condition of the concrete and the remote location of the dam, the estimated cost for installing anchors was very high. GEI and Dewberry & Davis performed a feasibility study for other alternatives. Based on the results of this study, the Town elected to engage GEI and Dewberry & Davis to design a new roller compacted concrete (RCC) dam downstream of the existing dam. This design is in progress at this time.