The West End Reservoir was constructed by the Town of Woodstock, Virginia in 1957 to provide water to the Town. Use of the reservoir was discontinued in 1979. The 42-foot high concrete gravity dam does not meet current spillway capacity as established by Virginia Dam Safety regulations and does not meet accepted stability criteria. The high hazard dam poses a risk to more than 75 homes and several roads if it were to fail.
When FEMA announced the availability of BRIC grants for dam removal in late 2023 the Town worked with Blossom Consulting and Engineering Inc. (BCE) to quickly submit an application to remove the dam before the deadline. FEMA requires that a Benefit Cost Analysis (BCA) be submitted as part of the application process and that the benefits of the project exceed the cost. One (1) publication was identified regarding dam removal, the Hands Mill Dam in Vermont presented in a paper by Stone Environmental. (Ultimately the Hands Mill dam was demolished by Mother Nature when heavy rains washed the dam out in July 2023 before it could be removed.)
It was straight forward to estimate the value of homes and infrastructure which would be destroyed if the dam were to fail, and the savings from not having to upgrade the dam. We used FEMA's DSS-Wise dam failure flood mapping and HCOM models to estimate the population at risk and potential for loss of life. FEMA flood mitigation projects are typically designed to protect people and structures against storms of a certain recurrence interval (i.e., 100-year flood, 500-year flood, etc.), and the BCA process required that we determine a "recurrence interval" for dam failure. This was a huge challenge. We considered the lifespan of the infrastructure (i.e., 50-100 years), its age, and likelihood that failure would occur in the next 50-100 years based on the age of the concrete, etc.
The authors will present some background for the BCA which other engineers and dam owners may find helpful when applying to FEMA for dam removal funding under BRIC and/or other similar funding streams for dam removal. Since FEMA employs outside reviewers who may not be familiar with Dam Safety criteria, considerable effort may be needed to educate them on the benefits of dam removal for risk reduction.
