Mapping a Flood … Before it Happens
Adapted from USGS press release
What's missing from flood forecasts? Maps. The only maps generally available today are maps used for planning. They are maps of theoretical floods, not maps of flooding forecast for an approaching storm. The U.S. Geological Survey (USGS) and the National Weather Service (NWS) have developed a way to bring flood forecasting and mapping together, producing flood maps for tomorrow's flood today. Developed by USGS scientists, the FloodPath software system can create a flood map days before a storm actually hits and put the map on the internet in time for those in harm's way to react.
The NWS issues a forecast flood hydrograph (plot of flow vs. time) for a particular location and USGS uses the hydrograph to create a flood-inundation map. The USGS has developed methods to make maps of these forecast floods for long stretches of a river near forecast points. These maps fill a critical information gap in flood forecasting: information on when and where floodwater from an approaching storm will arrive. The maps also show how deep the water is expected to be all across the floodplain. In essence, these methods combine to make a somewhat obscure "peak forecast elevation" into a map with flooded areas, times-of-arrival, and flood depths.
A number of new technologies and methods make the creation of flood forecast maps possible. First is the ability to get very accurate elevations throughout the floodplain quickly and affordably. This is done with "LIDAR" technology. Second is a computer program (TRIMR2D) that can simulate flood flows all across the floodplain and many, many miles downstream from the forecast point. Third is spatial analysis software (GIS) that turns the model results into maps and overlays them on other maps like a map of a neighborhood, or even onto an aerial photograph. Last is software (IMS) that makes the maps available on the Internet in a flexible and user-friendly way.
More information on this project can be obtained by:
A geographic information system (GIS) takes LIDAR elevations data and information from the TRIMR2D model to build maps of areas that likely will be inundated, based on the National Weather Service forecast flood.