Rabbit Creek Dam Inspection and Hazard Analysis
Client
USFS Region 1
Location
Harding County, South Dakota
Industry
Primary Service
Secondary Services
Dam Inspection, Drone Survey, Hazard Analysis, Geotechnical Investigation, Hydraulic Modeling
Project Description
Rabbit Creek Dam, a zoned earthfill structure southwest of Reva, South Dakota, serves as both a water retention facility and a roadway embankment for Highway 79. AESI was contracted by USFS Region 1 to conduct a comprehensive safety inspection, hazard analysis, and geotechnical investigation to assess the dam’s stability and risk profile.
The project included a full Potential Failure Mode Analysis (PFMA), a risk-based geotechnical assessment, and detailed stability modeling of the embankment. AESI evaluated seismic hazard and liquefaction potential, conducted an overtopping hydraulic scour study, and used advanced numerical modeling tools such as SLOPE/W for stability analysis and SEEP/W for seepage analysis. Additionally, drone survey data helped identify potential weak points, including low areas and possible sinkholes.
A key focus of the hazard analysis was reassessing the dam’s classification, which had previously been designated as Significant Hazard. However, prior evaluations had not accounted for the fact that Highway 79 runs along the embankment, posing a direct threat to motorists in the event of failure. Based on AESI’s findings, the classification was recommended for an upgrade from Significant to High Hazard. Following this assessment, AESI was contracted to conduct a feasibility study for dam decommissioning and later to develop a design for the selected decommissioning alternative.
Challenges
The hazard analysis required a detailed evaluation of complex failure modes, necessitating extensive numerical modeling to simulate different risk scenarios. Advanced tools such as HEC-HMS, SLOPE/W, and SEEP/W were used to analyze hydrologic and geotechnical conditions. Accurately assessing the dam’s failure impacts and potential life-safety risks demanded close coordination with USFS and a thorough review of all available data.
Solutions and Results
AESI’s comprehensive analysis led to the hazard classification being raised to High, in part due to the increased risk to motorists on Highway 79. This reclassification informed USFS decision-making, ultimately leading to the selection of dam decommissioning as the preferred course of action. AESI’s subsequent work on the feasibility study and decommissioning design ensured that the project moved forward with a well-documented and technically sound approach, prioritizing public safety and long-term site stability.
