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

Chris Timpson, MS, Southeast Market Directoro, Watershed Geo

Brad Cooley, PE, Senior Vice President, Watershed Geo

Bryan Scholl, Ph.D, PE, Director of Engineering, Watershed Geo

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.

Author Bio

Chris Timpson has worked in every facet of the geosynthetics industry including product development, technical service and sales. He is versatile in working with clients at all levels, including owners, municipalities, engineers, contractors and large, complex government agencies in the residential, commercial, industrial, federal and environmental sectors.

Brad Cooley is a Business Development, Sales, and Engineering Professional with over 15 years of progressive experience and success as a market focused and quality oriented leader.

Dr. Bryan Scholl has over 15 years of experience in hydraulic testing, design and consulting. His expertise includes laboratory steady-state and wave overtopping testing of levee and embankment erosion-control products, sediment transport, hydraulic and hydrologic numerical modeling and Froude scale physical model studies. He currently provides expertise in hydraulics, hydrology, erosion control and test methods for WatershedGeo.