Greenbrier State Park Dam – Not Your Average Walk in the Park

Wesley Hollenbach, PE, CFM, Dams Engineer, AECOM

Greenbrier State Park Dam, owned and operated by the Maryland Department of Natural Resources, is a 64-foot tall High Hazard earthen embankment dam located in Boonsboro, Maryland. The dam impounds a 30-acre public lake as part of the Maryland State Park system. The dam, constructed in 1965, has a history of seepage issues including incidents in 1996 and 2008 that warranted emergency response. On February 13, 2018, a small sinkhole was reported at the downstream toe, though no other indications of distress were observed. On April 16, 2018 multiple boils were observed along the downstream face and toe of the dam. These two incidents warranted activating the Emergency Action Plan (EAP) to Level 2 (potential failure). During the incident response, the Maryland Department of the Environment, Dam Safety Division directed that the reservoir be lowered, and four temporary sandbag rings be constructed around the seepage areas to monitor and control the seepage.

In short order, AECOM was contracted by the Maryland Department of General Services to investigate the condition at the dam and design a long-term rehabilitation of the dam. To investigate the condition at the dam, eleven soil borings were drilled in the embankment and abutments, seven vibrating wire piezometers (VWP) were installed, and various geophysical testing was performed. In coordination with the project team, AECOM developed a three-pronged approach which included: 1) rebuilding the sandbag rings with V-notch weirs and equipping them with weir monitors and turbidity meters, 2) installing fourteen additional VWPs and a rain gauge, and transmitting all of the monitoring data to a remote data system which sends out text and email alerts, and 3) replacing the malfunctioning lake drain valve. A synopsis of the investigation to date as well as how the data was used to influence the rehabilitation design will be presented.


Author Bio

Mr. Hollenbach is professional engineer with 8 years of experience working on dam related projects specializing in dam inspections, assessments, instrumentation, rehabilitation design, spillway integrity analyses and hydrologic and hydraulic analyses including watershed modeling, one- and two-dimensional dam breach inundation modeling and mapping.