Flood Inundation Mapping: Incorporating Emergency Management Experience into the Development of Future Flood Fighting Resources

For decades, hydrologists for the National Weather Service have been providing deterministic forecast hydrographs at designated points as their primary river forecast product. This legacy approach requires that emergency managers interpret a forecast hydrograph from a single point and extrapolate the impacts to their entire area of concern. An experimental NWS product is under development to enable emergency managers to visualize the extent of flooding. This flood inundation mapping product will support decisions made by emergency management during critical junctures in flood response. Past experience has proven that flood inundation mapping is a valuable tool for decision support during a flood event, however, critical questions remain about how and when it would be utilized by emergency managers. Feedback must be obtained to drive the development of the product to meet emergency manager requirements.

To answer these critical questions, the National Weather Service in conjunction with federal, state, and local partners performed a series of tabletop exercises to capture how emergency managers would utilize flood inundation mapping during simulated flooding situations. Two severe flooding situations in Texas, Hurricane Harvey in Houston and the Wimberley Flood of 2015 in Hays County, were the events simulated for the tabletop exercises. These events were selected due to their differences in timing and duration of flooding, with Harvey being a very well advertised, widespread, slow moving significant flood event and Wimberley being a rapid response, rapidly updating flood response event. These exercises were performed at two different locations to individually capture the state level and local level emergency manager application of flood inundation maps at different levels of flood response. This presentation will discuss some of the major findings provided by emergency responders about depth, timing, velocity, and confidence whose input will improve the design of these experimental flood inundation maps for high impact flood events.