A severely deteriorating spillway due to alkali silica reaction (ASR) and inadequate capacity made the old Lake Townsend dam a case for rapid action. The City of Greensboro’s project, which remediated these deficiencies, benefited the community by mitigating downstream flood risk and the associated damage to life and property, and significantly improved the reliability of the city’s primary source of drinking water.

Schnabel’s evaluation of the structure revealed that replacement of the spillway with a labyrinth weir was the best long-term solution. This award-winning $25 million project exemplified both design ingenuity and the mastery of complex challenges. Maintaining a full reservoir and uninterrupted city water supply throughout construction were essential, and required that the old dam perform well until the new structure was completed. Prompted by the discovery of deep cracks in the existing ogee weir, we initiated the emergency design of post-tensioned anchors to maintain its stability through construction of the new downstream labyrinth weir.

The tight, environmentally sensitive site called for careful planning, creative construction sequencing and techniques, staged diversion of construction activities for flood flows, and the mitigation of environmental impacts. Our early and frequent coordination with regulatory agencies and the city contributed to the positive outcome. The new dam was positioned immediately downstream of the stabilized old structure, which served as a cofferdam for construction. A 300-foot-wide labyrinth weir formed the replacement spillway. We designed the embankments with articulating concrete-block armoring to protect them from overtopping during extreme flood events and failure of upstream dams.

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