Evaluating Dam Breach Inundation for Largely Sedimented Reservoirs

This paper reports on a dam breach and inundation study for a dam in which 90 percent of the reservoir is now filled with sediment that has accumulated over its more than 100-year life. In this case, regulatory requirements indicated that the dam breach analysis should assume the reservoir is entirely filled to its maximum operating level with water. This condition drastically overestimates the potential area of inundation. To address this problem, three very different methods were used to model the outflow from a breach and the flow of water and sediment from the reservoir. The methods varied from simplified kinematics analysis to sophisticated particle analysis. The methods were 1) geotechnical kinematic analysis, 2) smoothed particle hydrodynamics (SPH) method, and 3) hydraulic analysis using HEC-RAS and mudflow analyses using FLO-2D. The use of three alternative methods addresses model uncertainty concerns. The SPH method is a computational method for simulating fluid flows. The results of the three methods showed the inundation remained in the upper reaches of the downstream channel away from populated areas.