Ripshin Lake Dam

S&ME was hired to evaluate the existing lake drain for Ripshin Lake Dam and prepare an Emergency Action Plan (EAP).  The dam consists of an approximately 43 feet tall by 395 feet long earthen dam impounding a 56-acre lake. The dam consists of a Small, High Hazard Dam due to location above nearby residences, Highway 19, and the Town of Roan Mountain. The dam was completed in the 1940s with modifications performed around 1992 that included raising the dam and construction of a concrete chute spillway.

S&ME evaluated the original steel siphon using visual and diving inspections, and ultrasonic testing.  A geotechnical exploration and stability were also performed for the dam.

The geotechnical evaluation and  research indicated the dam core was constructed using semi-hydraulic fill methods.  An original CMP outlet was also through the dam.  The repair design included two new 20-inch siphon drains; widening the dam crest 5 feet; construction of a chimney, blanket, and toe drain; and construction of an earthen stability berm.  S&ME provided CQA observation and testing services for the project. During lake drawdown, a surface depression was observed on the upstream slope indicating the potential for internal erosion along the CMP, and removal of a section of the embankment and CMP was performed and inspected.  It was found that the CMP had been grouted in place.  Excavated embankment soils were replaced with compacted, off-site borrow materials.  The upstream depression area was excavated and grouted.

When the embankment filling was approximately 10 feet below the crest, Hurricane Helene deposited approximately 15 inches of rainfall at the site over 2 days.  The storm flow was passed using the two new 20-inch siphon drains, pumps, and a temporary spillway notch without overtopping the dam.

The repairs were performed between September 2023 and January 2025.