Digital flood-inundation maps for a 9.5-mile reach of the Meramec River at Arnold, Missouri, were created by the U.S. Geological Survey (USGS) in cooperation with the United States Army Corps of Engineers, St. Louis Metropolitan Sewer District, Missouri Department of Transportation, Missouri American Water, Federal Emergency Management Agency Region 7, the City of Pacific, the City of Eureka, the City of Wildwood, and the City of Arnold. 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 Meramec River at Arnold, Missouri (station number 07019300). 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 at http://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 using the current stage-discharge relation at the Meramec River near Eureka streamgage and documented high-water marks from the floods of December 30, 2015. The hydraulic model was then used to compute 136 water-surface profiles for combinations of 8 different Mississippi River water surface elevations and flood stages at 1-foot (ft) intervals referenced to the streamgage datum and ranging from 22 ft or near bankfull to 51 ft, which exceeds the stage that corresponds to the maximum recorded peak flow. 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 0.5-ft vertical accuracy and 3.28-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 post flood recovery efforts.