Timothy D. Straub Adam E. Manaster Andrew P. Dunn 2020 <p>Digital flood-inundation maps for about an 8-mile reach of the Little Calumet River, Illinois, were created by the U.S. Geological Survey (USGS) in cooperation with the U.S. Army Corps of Engineers. The flood-inundation maps, which can be accessed through the USGS Flood Inundation Mapping Science website at <a href="https://www.usgs.gov/mission-areas/water-resources/science/flood-inundation-mapping-fim-program" data-mce-href="https://www.usgs.gov/mission-areas/water-resources/science/flood-inundation-mapping-fim-program">https://www.usgs.gov/mission-areas/water-resources/science/flood-inundation-mapping-fim-program</a>, depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at three USGS streamgages: Little Calumet River at South Holland, Ill. (USGS station 05536290); Little Calumet River at Munster, Indiana (USGS station 05536195); and Thorn Creek at Thornton, Ill. (USGS station 05536275). Near-real-time stages at these streamgages may be obtained on the internet from the USGS National Water Information System at <a data-mce-href="https://doi.org/10.5066/F7P55KJN" href="https://doi.org/10.5066/F7P55KJN">https://doi.org/10.5066/F7P55KJN</a> or the National Weather Service Advanced Hydrologic Prediction Service at <a data-mce-href="https://water.weather.gov/ahps/" href="https://water.weather.gov/ahps/">https://water.weather.gov/ahps/</a>, which also forecasts flood hydrographs at these sites.</p><p>Flood profiles were computed for the stream reaches using a one-dimensional unsteady flow step-backwater hydraulic model. The model performance was evaluated using historical streamflow measurements and the most current stage-discharge relations at the USGS streamgages at Little Calumet River at South Holland, Ill.; Little Calumet River at Munster, Ind.; and Thorn Creek at Thornton, Ill. The model was used to compute 24 water-surface profiles at 1-foot intervals referenced to the streamgage datum and ranging from bankfull to about the 0.2-percent annual-exceedance probability flood (500-year recurrence interval flood). The simulated water-surface profiles were then combined with a geographic information system digital elevation model (derived from light detection and ranging data having a 0.6-foot vertical accuracy and a 2-foot horizontal resolution) to delineate the area flooded at each water level.</p><p>The availability of these maps, along with internet information regarding current stage from USGS streamgages and forecasted high-flow stages from the National Weather Service, 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.</p> application/pdf 10.3133/sir20205074 en U.S. Geological Survey Flood-inundation maps for the Little Calumet River from Lansing to South Holland, Illinois, 2020 reports