Twin Lakes State Park Dam Rehabilitation

Twin Lakes State Park is a 548-acre recreational park located in Prince Edward County, Virginia that houses Goodwin Lake Dam and Prince Edward Dam. Both dams consist of earthen embankments with concrete overflow spillway and a riprap channel at the toe of the spillway chute. These dams are classified as low hazard. Stantec visited Goodwin Lake Dam and Prince Edward Dam in November 2018 to assess the damage following Hurricane Michael.

Goodwin Lake Dam show signs of overtopping along the full length of the berm, resulting in excessive erosion to the downstream face of the embankment. Riprap within the channel was displaced, developing an erosion hole approximately 20 feet deep. Prince Edward Lake Dam also appeared to have overtopped without causing significant erosion on the downstream face. The riprap was displaced downstream leading to a berm in conjunction with a fallen tree due to erosion along the left side of the channel. Sloughing on the downstream face of the embankment occurred due to ponding water behind the berm.

The Department of Conservation and Recreation (DCR) retained Stantec to design repairs of the spillway and restore the dam to original conditions. The original spillways were constructed on a soil foundation which scoured to expose bedrock during the storm event. With DCR’s best interest in mind Stantec recommended to redesign the spillway and not proceed with an in-kind design approach. The spillways were reconstructed using concrete placed directly against the rock foundation and included a riprap basin for energy dissipation at the downstream toe.

This presentation summarizes the design approach of both dams, including a redesign for long-term stability based on geotechnical involvement. The geotechnical involvement will highlight key concerns and issues with re-establishing cohesion between bedrock and structural fill following scouring occurrences.  Photographs throughout construction will also be included with this presentation.