DAM BREACH ANALYSIS - DYNAMIC MODELING
Diversified Engineering, Inc.
New Philadelphia, Ohio
DE was retained to build and run a dynamic model in the U.S. Army Corps of Engineers’ Hydrologic Engineering Center-River Analysis System (HEC-RAS) software to analyze potential flooding as a result of a breach in a dam at an upstream location.
A hydrologic model of the complex drainage system was constructed using AutoCAD Civil 3D and HEC-RAS software. The impoundment was located at the most upstream location, followed by a dam inline structure.
The downstream reach consisted of approximately 5.5 miles with two culvert sets, four bridges, and eleven junctions, terminating in a reservoir with surface water elevation control. Once the system geometry, Manning’s roughness coefficients, junction geometry, and necessary measurements and calculations pertaining to the hydraulic properties of the dam, culverts, and bridges were defined in the model, steady flow conditions were initially assumed to calibrate the downstream system under normal flow conditions.
Dam breach data were calculated using the National Weather Service’s Simplified Dam Break Flood Forecasting Model and added to the HEC-RAS model along with unsteady flow and boundary conditions. Due to the significant change in elevation across the model combined with the rapid change in velocity due to the dam breach, interpolations between cross sections were incorporated into the model to improve model accuracy.
Using the resulting dynamic model, it was determined that 24 properties would be at least partially flooded, with four residences and two roadways completely inundated should the dam fail.