This presentation will consider two dam breach studies developed in 2020 for Prince George’s County, Maryland as part of the Emergency Action Planning (EAP) process. We will provide an overview of the goals of each study and the unique challenges and constraints at each site to determine Population at Risk (PAR). We will review common hydraulic modeling judgement decisions including steady state vs. unsteady flow, and one-dimensional vs. two-dimensional modeling and discuss how to identify the right tool for each project that delivers accurate results at the appropriate level of effort and cost.

We will support this discussion with our real-world case studies in Prince Georges County. We will present the results of two hydraulic models, including graphics and video animations showing flood inundation and conveyance. One breach area affects a densely populated, urban area with a variety of floodplain obstructions and downstream crossings. The other breach area is in a virtually uninhabited stream and floodplain with minimal population at risk and forested floodplain. We show how each model was used to clearly identify and quantify specific property and persons at risk. We then summarized the implications for County managers and dam operators to reference as they develop their EAPs.