Risk Informed Assessment of Sympson Lake Dam

ABSTRACT ONLY - Sympson Lake is located just west of the City of Bardstown in Nelson County, Kentucky. The lake was constructed as a water supply dam in 1963 when U.S. Highway 62 was constructed over Buffalo Creek by the Kentucky Department of Highways. The dam is classified as a Significant or Class B, Moderate Hazard dam and is listed on the National Inventory of Dams (NID) under identification number KY00045.
Sympson Lake is the main water supply for the City of Bardstown and surrounding areas. The dam consists of a zoned earthen embankment constructed with a clay core and rockfill shell. The embankment stands at 73 feet tall with a crest elevation of 530.0 feet and side slopes at two horizontal and one vertical. U.S. Highway 62 runs along the 44-foot wide embankment crest including a 50-foot-long bridge that spans over the spillway.
In August 2021, a sinkhole appeared in the westbound lane of US-62 within the embankment of Sympson Lake Dam. The sinkhole prompted the Kentucky Transportation Cabinet (KYTC) Geotechnical Branch to contact HDR Engineering, Inc. (HDR) in October of 2021 to investigate the incident and potential dam safety impacts. This lead HDR, KYTC, City of Bardstown, and Kentucky Division of Water to conduct a Semi-Quantitative Risk Assessment (SQRA) to better understand the causes and mechanisms of observed distress (sinkholes and spillway seepage) and evaluate potential adverse impacts, such as probability of dam failure, inability to provide water supply, roadway damage, and public safety to motorists on U.S. Highway 62.
This paper & presentation will summarize the process, findings, and lessons learned the team identified for the SQRA with a dam experiencing signs of distress with non-life loss consequences.