In September 2014, Flat Top Lake Association, Inc. (FTLA), private owner of the Flat Top Lake Dam, received an Order for Compliance from the West Virginia Department of Environmental Protection (WVDEP). At that time, the dam’s primary and emergency spillways were inadequately sized to satisfy WVDEP’s 6-hour probable maximum precipitation (PMP) design storm requirement. The dam is a high hazard, 33-foot-high earthen dam located in Raleigh County, West Virginia that impounds a normal pool volume of 3,150 acre-feet. The dam was constructed in the 1950s, and was one of many dams built prior to the Dam Control and Safety Act of 1972 that have been deemed noncompliant with current dam regulations. Numerous design configurations were considered for modification of the dam but were either cost prohibitive, aesthetically unacceptable to lake residents, or otherwise not feasible. Consideration was ultimately given to an overtopping protection design using a fabric formed articulating block mattress (ABM), which would satisfy WVDEP’s design criteria and the owner’s budgetary constraints.
The design called for placement of ABM over the entire dam face, from the crest to the toe and extending beyond both embankment groins. Anchor trenches were constructed along the left and right edges of the ABM, and a reinforced concrete deadman anchor trench was constructed at the crest. The ABM was connected to the deadman anchor, which was then overlaid with a reinforced concrete roadway to create a unified anchoring structure. It was determined that a hydraulic jump would likely occur on the dam face during overtopping, as flows through the emergency spillway would create substantial backwater at the toe prior to any overtopping event. Additional protection against uplift of the ABM due to the hydraulic jump was provided in the form of percussion driven anchors in the affected area.
The modification design was approved by WVDEP and is the first known use of ABM for overtopping protection in West Virginia. Construction proceeded quickly and was nearly complete by December 2017. Using ABM as a solution for overtopping protection saved the owner hundreds of thousands of dollars compared to more commonplace designs. Moving forward, the use of ABM in dam overtopping protection could serve to meet the need for an affordable and reliable means of bringing existing dams into compliance with 21st century hydrologic design criteria.
In September 2014, Flat Top Lake Association, Inc. (FTLA), private owner of the Flat Top Lake Dam, received an Order for Compliance from the West Virginia Department of Environmental Protection (WVDEP). At that time, the dam’s primary and emergency spillways were inadequately sized to satisfy WVDEP’s 6-hour probable maximum precipitation (PMP) design storm requirement. The dam is a high hazard, 33-foot-high earthen dam located in Raleigh County, West Virginia that impounds a normal pool volume of 3,150 acre-feet. The dam was constructed in the 1950s, and was one of many dams built prior to the Dam Control and Safety Act of 1972 that have been deemed noncompliant with current dam regulations. Numerous design configurations were considered for modification of the dam but were either cost prohibitive, aesthetically unacceptable to lake residents, or otherwise not feasible. Consideration was ultimately given to an overtopping protection design using a fabric formed articulating block mattress (ABM), which would satisfy WVDEP’s design criteria and the owner’s budgetary constraints.
The design called for placement of ABM over the entire dam face, from the crest to the toe and extending beyond both embankment groins. Anchor trenches were constructed along the left and right edges of the ABM, and a reinforced concrete deadman anchor trench was constructed at the crest. The ABM was connected to the deadman anchor, which was then overlaid with a reinforced concrete roadway to create a unified anchoring structure. It was determined that a hydraulic jump would likely occur on the dam face during overtopping, as flows through the emergency spillway would create substantial backwater at the toe prior to any overtopping event. Additional protection against uplift of the ABM due to the hydraulic jump was provided in the form of percussion driven anchors in the affected area.
The modification design was approved by WVDEP and is the first known use of ABM for overtopping protection in West Virginia. Construction proceeded quickly and was nearly complete by December 2017. Using ABM as a solution for overtopping protection saved the owner hundreds of thousands of dollars compared to more commonplace designs. Moving forward, the use of ABM in dam overtopping protection could serve to meet the need for an affordable and reliable means of bringing existing dams into compliance with 21st century hydrologic design criteria.