NEAR-REAL-TIME FLOOD INUNDATION MAPPING PILOT PROJECT

As part of the U.S. Geological Survey (USGS) Seattle Natural Hazards Project, USGS scientists are developing a flood-inundation mapping methodology that will generate and distribute storm-specific inundation forecasts in near-real-time over the Internet. Existing flood maps are based on statistically determined recurrence intervals, for example, the often mentioned “100-year” flood. Currently, there are no operational techniques for timely creation of flood maps depicting imminent storm-specific inundation. Flood forecasts generated by the National Weather Service River Forecast Centers (RFCs) for selected forecast points, usually USGS-operated streamflow stations, are of limited use at locations other than the forecast points. A new robust, stable two-dimensional hydraulic model was used in this project to extend the RFC flood forecast to a 23-kilometer reach of river. Very high accuracy (better than 1-foot accuracy) elevation data are being used in the hydraulic model, which allows the generation of flood maps with a high level of detail. Geographic Information Systems provide the map generation capability. The maps are provided over the Internet using emerging Internet map server technology, which allows scale-dependent map symbology and themes, and allows the user to select features of particular individual interest for display along with the inundation forecast.