Geospatial datasets and hydraulic model for the flood-inundation study of Fourmile Creek at Silver Grove, Kentucky

Digital flood-inundation maps for a 3.4-mile reach of Fourmile Creek at Silver Grove, Kentucky, were created by the U.S. Geological Survey (USGS) in cooperation with the City of Silver Grove and the U.S. Army Corps of Engineers Louisville District. Because the City of Silver Grove is subject to flooding from Fourmile Creek and the Ohio River (backwater flooding up Fourmile Creek), a set of flood-inundation maps was created for each flooding source independently and for combinations of possible flooding scenarios. The flood-inundation maps depict estimates of the areal extent and depth of flooding corresponding to a range of different gage heights (gage height is commonly referred to as “stage,” or the water-surface elevation at a streamgage) at the USGS streamgage on Fourmile Creek at Grays Crossing at Silver Grove, Kentucky (station number 03238785), and the USGS streamgage on Fourmile Creek at Highway 8 at Silver Grove, Kentucky (station number 03238798). Near-real-time stages at these streamgages can be obtained on the internet from the USGS National Water Information System at https://waterdata.usgs.gov/. The USGS streamgage on the Ohio River at Cincinnati, Ohio (station number 03255000) is also important in this study because the National Weather Service (NWS) Advanced Hydrologic Prediction Service (AHPS), at https://water.weather.gov/ahps/, forecasts flood hydrographs for this site (NWS AHPS site CCNO1). The NWS AHPS forecast peak-stage information can be used in conjunction with the maps developed in this study to show predicted areas of flood inundation.

Flood profiles were computed for the Fourmile Creek reach by means of a one-dimensional, step-backwater hydraulic model developed by the U.S. Army Corps of Engineers. The hydraulic model was calibrated by using the current stage-discharge relation (USGS rating number 1.1) at USGS streamgage 03238785, Fourmile Creek at Grays Crossing at Silver Grove, Kentucky. The model was then used to compute water-surface profiles for 83 combinations of flood stages on the Ohio River and Fourmile Creek ranging from approximately baseflow to greater than a 2-percent annual exceedance probability event. An additional 50 water-surface profiles were computed for backwater-only flood profiles (from the Ohio River) for flood elevations (referenced to the North American Vertical Datum of 1988 [NAVD 88]) at 1-ft intervals referenced to USGS streamgage 03238798, Fourmile Creek at Highway 8 at Silver Grove, Ky., and ranged from approximately normal pool (460 ft NAVD 88) to greater than a major flood stage on the Ohio River (509 ft NAVD 88). The computed water-surface profile information was then combined with a digital elevation model derived from light detection and ranging (lidar) data to delineate the approximate areas flooded.

The digital flood-inundation maps are available through the USGS Flood Inundation Mapper application (https://fim.wim.usgs.gov/fim/) that presents map libraries and provides detailed information on flood extent and depths for selected sites. The flood-inundation maps developed in this study, in conjunction with the real-time stage data from the USGS streamgages on Fourmile Creek at Silver Grove, Kentucky, and forecasted stream stages from the NWS AHPS, are intended to provide information that can help inform the public about potential flooding and provide emergency management personnel with a tool to efficiently manage emergency flood operations, such as evacuations and road closures, and assist in postflood recovery efforts.

This data release is comprised of (1) a model archive of the hydraulic model for Fourmile Creek; (2) depth grids of the flood-inundation maps for backwater-only flooding; (3) depth grids of the flood-inundation maps for combined flooding scenarios; (4) shapefiles of the backwater-only flood-inundation maps; and (5) shapefiles of the flood-inundation maps for combined flooding scenarios. Depth grids and shapefiles for the two types of flooding are discussed in four separate metadata files.