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Flood inundation and flood depth for the Yellow River in Gwinnett County, Georgia based on water-surface elevation at the U.S. Geological Survey streamgages Yellow River, near Snellville, Georgia (02206500) and Yellow River at Ga. 124, near Lithonia, Geor

March 14, 2019

The digital flood-inundation maps included in this data release were developed for a 16.4-mile reach of the Yellow River from 0.5-mile upstream of River Drive to Centerville Highway (Georgia State Route 124), Gwinnett County, Georgia (Ga.) to depict estimates of the areal extent and depth of flooding corresponding to selected water levels (stages) at two U.S. Geological Survey (USGS) streamgages in the mapped area. The maps for the 9.0-mile reach from 0.5-mile upstream of River Drive to Stone Mountain Highway (US Route 78) are referenced to the Yellow River, near Snellville, Georgia (Ga.; station 02206500), and the maps for the 7.4-mile reach from Stone Mountain Highway to Centerville Highway are referenced to the streamgage Yellow River at Ga. 124, near Lithonia, Ga. (02207120). Real-time stage information from these streamgages can be used with these maps to estimate near real-time areas of inundation. The forecasted peak-stage information for the USGS streamgages Yellow River, near Snellville, Ga. (02206500), and Yellow River at Ga. 124, near Lithonia, Ga. (02207120), can be used in conjunction with the maps developed for this study to show predicted areas of flood inundation. A one-dimensional step-backwater model was developed using the U.S. Army Corps of Engineers Hydrologic Engineering Center's River Analysis System (HEC-RAS) software for the Yellow River and was used to compute flood profiles for this 16.4-mile reach of the Yellow River. The hydraulic model was then used to simulate 16 water-surface profiles at 1.0-foot (ft) intervals at the Yellow River near Snellville, Ga. streamgage and 17 water-surface profiles at 1.0-ft intervals at the Yellow River near Lithonia, Ga. streamgage. At the Yellow River near Snellville, Ga. streamgage, the profiles ranged from a stage of 18.0 ft, which is 819.1 ft above the North American Vertical Datum of 1988 (NAVD 88), to a stage of 33.0 ft, which is 834.1 ft above NAVD 88. At the Yellow River at Ga. 124, near Lithonia, Ga. streamgage, the profiles ranged from the National Weather Service action stage of 13.0 ft, which is 732.5 ft above NAVD 88, to a stage of 29.0 ft, which is 748.5 ft above NAVD 88. 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 5.0-ft horizontal resolution-to delineate the area flooded at each 1.0-ft interval of stream stage for each streamgage. Information about the study, floods, and methods used can be found in the USGS Scientific Investigations Report 2019-5009 online at https://doi.org/10.3133/sir20195009.

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