Digital flood-inundation maps for a 6.4-mile reach of the White River in Indianapolis, Indiana, from 0.3 miles upstream of Michigan Street to the Harding Street Generating Station dam (at the confluence with Lick Creek), were created by the U.S. Geological Survey (USGS) in cooperation with the Indiana Office of Community and Rural Affairs. The flood-inundation maps, which can be accessed through the USGS Flood Inundation Mapping Science Web site at http://water.usgs.gov/osw/flood_inundation/, depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at the USGS streamgage on the White River at Indianapolis, Ind. (station number 03353000). Near-real-time stages at this streamgage may be obtained on the Internet from the USGS National Water Information System at http://waterdata.usgs.gov/or the National Weather Service (NWS) Advanced Hydrologic Prediction Service athttp://water.weather.gov/ahps/, which also forecasts flood hydrographs at this site.

Flood profiles were computed for the stream reach by means of a one-dimensional step-backwater model. The model was calibrated by using the current stage-discharge relations at three USGS streamgages: the White River at Indianapolis (station number 03353000), the White River at Michigan Street at Indianapolis (station number 03352953), and the White River at Stout Generating Station at Indianapolis (station number 03353611).

The hydraulic model was then used to compute 11 water-surface profiles for flood stages at 1-foot (ft) intervals referenced to the White River at Indianapolis streamgage datum and ranging from 10 ft, or the NWS “action stage,” to 20 ft, which is the highest stage in the stage-discharge relation for the streamgage and the NWS “moderate flood stage.”

The simulated water-surface profiles were then combined with a geographic information system digital elevation model (derived from light detection and ranging [lidar] data having a vertical 0.183-ft root mean squared error and 5.0-ft horizontal resolution) to delineate the area flooded at each water level.

The availability of these maps, along with Internet information regarding current stage from the USGS streamgage and forecasted high-flow stages from the NWS, will provide emergency management personnel and residents with information that is critical for flood response activities such as evacuations and road closures, as well as for postflood recovery efforts.