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

By: Jonathan W. Musser**

                            https://doi.org/10.3133/sim3338

#### Links

-                                                                                                                             Document:                                                                                                                                                                                                                                                  **Report - SIM 3338 Pamphlet**                                                                                                     (1.56 MB pdf)                                                                                                                                     
- Sheets:                               - **Sheet01 - Gage height of 6.0 feet and an elevation of 966.6 feet at streamgage 02335700**                            (18.1 MB pdf)                        
  - **Sheet02 - Gage height of 6.5 feet and an elevation of 967.1 feet  at  streamgage 02335700**                            (18.1 MB pdf)                        
  - **Sheet03 - Gage height of 7.0 feet and an elevation of 967.6 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet04 - Gage height of 7.5 feet and an elevation of 968.1 feet at streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet05 - Gage height of 8.0 feet and an elevation of 968.6 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet06 - Gage height of 8.5 feet and an elevation of 969.1 feet at   streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet07 - Gage height of 9.0 feet and an elevation of 969.6 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet08 - Gage height of 9.5 feet and an elevation of 970.1 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet09 - Gage height of 10.0 feet and an elevation of 970.6 feet at   streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet10 - Gage height of 10.5 feet and an elevation of 971.1 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet11 - Gage height of 11.0 feet and an elevation of 971.6 feet at streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet12 - Gage height of 11.5 feet and an elevation of 972.1 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet13 - Gage height of 12.0 feet and an elevation of 972.6 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet14 - Gage height of 12.5 feet and an elevation of 973.1 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet15 - Gage height of 13.0 feet and an elevation of 973.6 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet16 - Gage height of 13.5 feet and an elevation of 974.1 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet17 - Gage height of 14.0 feet and an elevation of 974.6 feet at  streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet18 - Gage height of 14.5 feet and an elevation of 975.1 feet at   streamgage 02335700**                            (18.2 MB pdf)                        
  - **Sheet19 - Gage height of 15.0 feet and an elevation of 975.6 feet at  streamgage 02335700**                            (18.2 MB pdf) 
- Metadata:                               - **SIM 3338 - Depth-grid Metadata**                            (62 KB html)                        
  - **SIM 3338 - Inundation Layer Metadata**                            (71 KB html) 
- Raw Data:  **SIM 3338 - Depth-grids and Inundation Layers**                            (133 MB)                        
- Download citation as:  RIS                         |                         Dublin                            Core

#### Abstract

First posted August 20, 2015

**For additional information, contact:**
Director, South Atlantic Water Science Center  U.S. Geological Survey 720 Gracern Road Columbia, SC 29210 http://www.usgs.gov/water/southatlantic/

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

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