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Flood-inundation maps for Big Creek from the McGinnis Ferry Road bridge to the confluence of Hog Wallow Creek, Alpharetta and Roswell, Georgia

Scientific Investigations Map 3338
Prepared in cooperation with the cities of Alpharetta, and Roswell, Georgia
By:
https://doi.org/10.3133/sim3338

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Abstract

Digital flood-inundation maps for a 12.4-mile reach of Big Creek that extends from 260 feet above the McGinnis Ferry Road bridge to the U.S. Geological Survey (USGS) streamgage at Big Creek below Hog Wallow Creek at Roswell, Georgia (02335757), were developed by the USGS in cooperation with the cities of Alpharetta and Roswell, Georgia. The 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 at Big Creek near Alpharetta, Georgia (02335700). Real-time stage information from this USGS streamgage may be obtained at http://waterdata.usgs.gov/ and can be used in conjunction with these maps to estimate near real-time areas of inundation. The National Weather Service (NWS) is incorporating results from this study into the Advanced Hydrologic Prediction Service (AHPS) flood-warning system http://water.weather.gov/ahps/). The NWS forecasts flood hydrographs for many streams where the USGS operates streamgages and provides flow data. The forecasted peak-stage information for the USGS streamgage at Big Creek near Alpharetta (02335700), available through the AHPS Web site, may 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 HEC–RAS software for Big Creek and was used to compute flood profiles for a 12.4-mile reach of Big Creek. The model was calibrated using the most current (2015) stage-discharge relations at two USGS streamgages on Big Creek: Big Creek near Alpharetta (02335700) and Big Creek below Hog Wallow Creek at Roswell (02335757). The hydraulic model was then used to simulate 19 water-surface profiles at 0.5-foot intervals at the Big Creek near Alpharetta streamgage. The profiles ranged from just above bankfull stage (6.0 feet) to approximately 1.95 feet above the highest recorded water level at the Alpharetta streamgage site (15.0 feet). 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 3.0-foot horizontal resolution—to delineate the area flooded at each 0.5-foot interval of stream stage.

The availability of these maps, when combined with real-time stage information from USGS streamgages and forecasted stream stage from the NWS, provides emergency management personnel and residents with critical information during flood-response activities such as evacuations and road closures, in addition to post-flood recovery efforts.

Suggested Citation

Musser, J.W., 2015, Flood-inundation maps for Big Creek from the McGinnis Ferry Road bridge to the confluence of Hog Wallow, Alpharetta and Roswell, Georgia: U.S. Geological Survey Scientific Investigations Map 3338, 19 sheets, 10-p. pamphlet, http://dx.doi.org/10.3133/sim3338.

ISSN: 2329-132X (online)

Study Area

Table of Contents

  • Abstract
  • Introduction
  • Constructing Water-Surface Profiles
  • Inundation Mapping
  • Summary
  • References Cited
Publication type Report
Publication Subtype USGS Numbered Series
Title Flood-inundation maps for Big Creek from the McGinnis Ferry Road bridge to the confluence of Hog Wallow Creek, Alpharetta and Roswell, Georgia
Series title Scientific Investigations Map
Series number 3338
DOI 10.3133/sim3338
Year Published 2015
Language English
Publisher U.S. Geological Survey
Publisher location Reston, VA
Contributing office(s) South Atlantic Water Science Center
Description Report: vi, 10 p.; 19 Sheets: 29.0 x 30.0 inches; Metadata; Raw Data
Country United States
State Georgia
City Alpharetta, Roswell
Other Geospatial Big Creek, Hog Wallow Creek
Online Only (Y/N) Y
Additional Online Files (Y/N) Y
Google Analytic Metrics Metrics page
Additional publication details