Calculating Annual Flood Damages Reduced Using The Corps Water Management System

Computing annual flood damages reduced using the Corps Water Management System (CWMS) improves the Annual Flood Damages Reduced estimates developed by US Army Corps of Engineers (USACE) District Offices. This approach to estimate annual flood damages reduced uses the latest spatial structural and/or agricultural inventories, inundation mapping, and reservoir operations to develop a more informed picture of how USACE dam and levee projects reduce flood damages across the nation. Each year, USACE District Offices are required to report the total dollar value of flood damages reduced by their dam and levee projects. The total flood damages reduced for each District are combined into a single annual report organized by state, and USACE Headquarters then delivers this report to Congress. Historically, flood damages reduced have not been consistently calculated across the country. Many USACE Districts used some sort of aggregated stage-damage curves. For a specified river reach, the max stage at the local gage would be entered on the stage-damage curve, providing the flood damages reduced for the floodplain. While these aggregated stage-damage curves are indexed for inflation each year, they do not consider any changes to land use in the floodplain since development decades ago, nor would the curves reflect any future changes. Over the last decade, USACE have developed CWMS models for watersheds across the country through the CWMS National Implementation Plan. CWMS models integrate real-time data acquisition, database storage, flow forecasting of watershed runoff, reservoir operation decision support, river profile modeling, inundated area determination, consequence/damage analysis, and information dissemination into a comprehensive suite of software, supporting water management decision processes. For a specific flood event, the USACE District can use the CWMS model to simulate what the flood inundation and flood damages would be if the USACE dams and levees were not present. These damages can then be compared against a CWMS simulation of the actual event, estimating the flood damages reduced by the USACE projects. This new methodology of calculating annual flood damages reduced by leveraging CWMS models allow USACE Districts to more accurately estimate the dollar value of flood damages reduced by their dam and levees, and broadcast the benefit of USACE projects to the nation.