A Case Study of Dam Overtopping Protection with an Engineered Turf Revetment in Loudoun County, VA

Many existing earthen dams in Virginia do not meet requirements of the Virginia Dam Safety Act.  Reasons for failing to meet Dam Safety Act requirements include insufficient spillway capacity and inadequate embankment height for the required design event.  Inadequate spillways and embankment heights increase the likelihood of dam overtopping.  Dam overtopping can lead to partial or complete failure of a dam, potentially causing loss of life and property.  To bring such an existing dam back into compliance, owner options include increasing spillway capacity, raising the dam embankment height, or providing overtopping protection on the downstream face.  Overtopping protection can economically bring a dam into compliance and mitigate potential risk of failure.

In 2017 the Virginia Soil and Water Conservation Board approved a Guidance Document on the Use of Overtopping Protection Systems on Existing Impounding Structures.  An example of an acceptable overtopping protection system is an engineered turf revetment system.  This overtopping solution is specifically engineered to provide armoring of the downstream side against high velocity flows.  In addition to hydraulic performance, the engineered turf revetment system provides the aesthetics of natural vegetation and is cost-effective when compared with other traditional hard armoring systems.

A Homeowner’s Association (HOA) representing 829 homes in Loudoun County, VA faced a significant challenge.  Within the community is a large stormwater pond covering approximately 5 acres and having an earthen berm running parallel to the U.S. Route 15 Bypass. In 2014, the Virginia Department of Conservation & Recreation (VA DCR) notified the HOA that the community dam, referred to herein as Richmond Square Dam, was deemed “high-hazard” and must be brought into compliance with state regulations.  The HOA decided to provide overtopping protection of the earthen berm and selected an engineered turf revetment system as the preferred technology.

The presentation will provide an overview of the design, permitting, and installation of the engineered turf revetment system on Richmond Square Dam.  Topics include a description of the system, a summary of the required technical evaluations performed in accordance with the Virginia DCR overtopping guidance document, and a chronology of the installation process.  The presentation will end with a photographic documentation of the completed project.