Lake Tomahawk Dam

Lake Tomahawk Dam is a High Hazard Dam located in Black Mountain, North Carolina. The approximate 10-acre lake is a central feature of the popular Lake Tomahawk Park in the Town of Black Mountain. A Spillway Design Flood Analysis performed by S&ME indicated the dam could successfully pass a 100-year storm event, but could not safely pass and/or store the 1/3 Probable Maximum Precipitation (PMP) design storm event without overtopping the dam embankment. Overtopping of earthen dams can lead to rapid erosion of the embankment and, ultimately, dam failure.

As a cost-beneficial alternative to spillway modifications, an Articulated Concrete Block Revetment System was constructed on the downstream side of the dam as permanent armoring for overtopping events.

S&ME prepared engineering plans for the construction of the ACB overtopping protection at Lake Tomahawk Dam and provided Quality Assurance services during the construction phase. Construction was completed in June 2024, just a few months before Helene brought 3-day rainfall of over 12 inches to the North Carolina mountains. Floodwaters from Helene resulted in Lake Tomahawk Dam overtopping by a few inches. The overtopping flows scoured the vegetative layer and exposed the ACBs in a small section along the spillway, but the system protected the earthen section of the dam as intended. The extreme erosive forces from the event were evident by the significant damage to the infrastructure immediately downstream.