Interactive websites and digital maps of flood inundation for select areas in Georgia are available on sites hosted by the U.S. Geological Survey (USGS) and the National Weather Service (NWS). The mapped and modeled areas to date include the Flint River in Albany, Peachtree Creek in Atlanta, Sweetwater Creek in Cobb and Douglas Counties, and Suwanee Creek in Gwinnett County.
The inundation maps provide water-surface elevations in relation to the North American Vertical Datum of 1988 (NAVD 88) and show flood extent and water depths, so emergency managers and the public can see and prepare for potential flooding.
The AHPS flood-inundation website, shown above, has background map images obtained from the Google Maps satellite with multiple zoom levels. Water depth is color coded in shades of blue, and the transparency level can be modified. Additional gage information, such as flood categories, flood-impact statements, and forecasts can be obtained at this site. Other tabbed information available at this website include Hydrograph, River at a Glance, Download, Weekly Chance of Exceeding Levels, and Chance of Exceeding Levels During Entire Period.
The USGS FIM website, shown above, depicts flood-inundated areas on a choice of backgrounds (street map, satellite imagery with labels, or topography) as well as additional information about the streamgaging location and the area(s) of inundation. Once a streamgage is selected, an information window is displayed that includes additional tabbed information the user may find helpful. The first tab is Flood Tools, which include one or two slide bars to set the gage height and elevation at the streamgage(s). The inundated area changes based on the streamgage heights. The second tab displays recent hydrograph(s) for the streamgage(s). The third tab provides access to the NWS prediction for the streamgage. The fourth tab provides access to the U.S. Environmental Protection Agency Hazus data for the site if it exists. The next two tabs show images from webcams, if they exist, and the final tab provides information about the site, including published reports.
Other tools included with the FIM mapper are zoom history, latitude and longitude connected to the mouse pointer, a search engine, and additional layers which can be displayed, such as NWS radar, flood watches and (or) warnings, and AHPS forecast sites.
The U.S. Army Corps of Engineers Savannah District is currently developing flood inundation maps for the Chattahoochee River in Atlanta and the Ocmulgee River in Macon. The USGS is collecting peak water-level data using self-logging sensors that are deployed along the channel reaches of both these study areas. The water-level data will be used to calibrate the USACE models that are used to develop the flood inundation maps. The flood inundation maps will be hosted on the AHPS and FIM websites.