Incorporating Dam Inundation Risk within a FEMA RiskMAP Project: A Pilot Study

ABSTRACT ONLY - Washington County, located in eastern New York on the state boundary with Vermont, has over 80 dams spread throughout the county. A FEMA Risk Map study is underway to update and modernize Washington County's floodplain mapping information. Though this study includes over 700 miles of regulatory floodplain mapping, it does not address potential risk to areas downstream of dams due to potential future dam failure. To provide dam inundation risk information, FEMA included the development of enhanced dam failure non-regulatory products in the mapping contractor (STARR II's) study scope. STARR II and FEMA worked with NYSDEC to screen the dams to determine which would be priority for study. Screening parameters including hazard classification, dam height and size, availability of inundation mapping, and development in areas immediately downstream of the dams, were used to identify 15 dams for study. DSS-WISE, a web-based two-dimensional dam-break flood modeling software was selected to use in the analysis for its ability to generate inundation mapping and other products efficiently with minimal input. The outputs from DSS-WISE (Version 3.0) such as inundation area, depth grids, and velocity grids will be incorporated into Washington County's flood risk database to provide planning level information that Emergency Managers and other community leaders can use to make preliminary decisions regarding the dams' downstream risks. This project represents the first time FEMA Region 2 has addressed risk to areas downstream of dams due to potential dam break incidents specifically within the non-regulatory products. The presentation will include discussion of the dam screening process, an overview of the use of DSS-WISE in this application (including discussion of recently added features), and a summary of information that can be produced and integrated into a Flood Risk Database to communicate risk to downstream areas that is not typically provided in FEMA's regulatory flood information.