Risk reduction measures are planned for Prison Pond Dam in Windsor, VT. A brief overview of these measures and other considerations are provided below. For more information, please refer to the August, 2023 Dam Safety Inspection Report and subsequent Risk Reduction Memo. Please contact the Dam Safety Program with questions or concerns at anr.damsafety@vermont.gov. The dam is owned by the Department of Fish and Wildlife.
- Dam History: The dam was reportedly originally constructed in 1925 for fire protection at the nearby Southeast State Correctional Facility and has undergone reconstruction in 1950 and 1989. Prior to 2017, the dam was owned by the Department of Building and General Services (BGS). Vermont closed in the correctional facility citing financial reasons. BGS transferred a portion of the property and Prison Pond Dam to the Department of Fish & Wildlife. The property and dam are now part of the Windsor Grasslands Wildlife Management Area.
- Dam Configuration: The dam is a composite stone masonry, earth fill, and concrete dam with a principal spillway, low-level-outlet pipe (pond drain), and water supply pipe (fire suppression). The water supply pipe has not been in use for some time as the system was modified to use a well for water supply instead of Prison Pond.
- Condition: The dam has been rated in POOR condition since at least 2006 with deterioration including structural cracking of the principal spillway training walls, as well as concrete cracking and leakage through the crest wall which results in erosion of the downstream embankment slope. Following an inspection on August 3, 2023, increased leakage and deterioration were noted resulting in the dam receiving an UNSATISFACTORY condition rating. In response, the Dam Safety Program is requiring Fish & Wildlife implement risk reduction measures.
- Potential Consequences: The dam is currently classified as a SIGNIFICANT hazard potential, meaning failure or mis-operation of the dam will likely result in no probable loss of human life but is anticipated to cause some degree of property/economic damage, environmental damage, and disruption. Based on a simplified dam failure analysis performed by the Dam Safety Program, failure of the dam is anticipated to overtop Pond Road, Marton Road, and a private driveway leading to the 2505 County Rd residence. No homes/buildings are anticipated to be impacted/flooded in the event of an uncontrolled release or dam failure.
- Risk Reduction Measures: The following measures will be implemented: brush/tree clearing within the dam footprint to allow for proper monitoring/inspection, and lowering of the normal water level by 2.4 feet by cutting a notch in the existing principal spillway crest. The lowered water level results in a 33% reduction in normal pool storage volume. Failure of the dam under this reduced storage volume is no longer anticipated to overtop Marton Road or the downstream private driveway. These risk reduction measures are being implemented as an interim step. Additional risk reduction measures will be implemented as necessary based observations made during routine monitoring efforts. The risk reduction measures are being performed in coordination with local, state, and federal regulatory entities.
- Impacts to Existing Uses: Warning sings have been posted to stay off the dam and out of the pond. The lower water level will result in a reduction of pond surface area from 0.9 acres to 0.8 acres and a reduction in normal pool volume from 6.3 acre-ft to 4.2 acre-ft.
- Next Steps: The Department of Fish and Wildlife is to move forward with either a dam reconstruction or removal project. Both options will require an engineered design and permits including a Dam Order.
- Regulatory Jurisdiction: The dam is a non-power, non-federal dam and is therefore under the regulatory jurisdiction of the Vermont DEC Dam Safety Program and State Statute 10 V.S.A. Chapter 43: Dams.
Prison Pond Dam (2008)
Concrete Crest Wall (August, 2023)
Concrete Crest Wall Leakage Example (August, 2023)
Principal Spillway (August, 2023)
Leakage Erosion Example (August, 2023)
Spillway Concrete Cracking Example (August, 2023)
