Two-Dimensional Dam-Breach Flood Modeling and Inundation Mapping with Cascading Failures

The present paper presents a dam-breach study in support of Shelby County Department of Development Services for developing emergency action plans and for other planning purposes. The study involved two-dimensional numerical modeling of four dams located in the Oak Mountain State Park, which are within the Cahaba Valley Creek Basin (a.k.a. Bishop Creek): Double Oak Lake, Lake Tranquility, Beaver Lake, and Lunker Lake. The modeling and simulations were carried out using the DSS-WISE software and included the sunny day breach and probable maximum flood (PMF) breach scenarios. A PMF base scenario with no dam breaches was also simulated. The simulations included individual breaching of each dam as well as the cascading failure of the Lunker Lake and Beaver Lake Dams. Modeled PMF conditions were based on the inflow design flows generated by the 90% of the probable maximum precipitation (PMP) distributed over the upstream drainage basins of the dams. Hydrologic analyses were carried out using USACE HEC-HMS model to estimate inflows to the lakes. Hydrologic data for Bishop Creek was obtained from a hydrologic study performed as part of FEMA’s flood insurance study. The paper presents the results of the hydrologic study and the two-dimensional modeling of cascading and individual dam-breach flood modeling and inundation mapping. It discusses how the simulation results were used by the county for the development of emergency action plans and for other purposes.