Flood-Inundation Maps for Big Creek from the Mcginnis Ferry Road Bridge to the Confluence of Hog Wallow Creek, Alpharetta and Roswell, Georgia
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Prepared in cooperation with the cities of Alpharetta and Roswell, Georgia Flood-Inundation Maps for Big Creek from the McGinnis Ferry Road Bridge to the Confluence of Hog Wallow Creek, Alpharetta and Roswell, Georgia Pamphlet to accompany Scientific Investigations Map 3338 U.S. Department of the Interior U.S. Geological Survey Cover. Left, Big Creek Greenway in Alpharetta, Georgia; right, Vickery Creek Trail in Roswell, Georgia (photographs by Jonathan W. Musser, U.S. Geological Survey). 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 Prepared in cooperation with the cities of Alpharetta and Roswell, Georgia Pamphlet to accompany Scientific Investigations Map 3338 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior SALLY JEWELL, Secretary U.S. Geological Survey Suzette M. Kimball, Acting Director U.S. Geological Survey, Reston, Virginia: 2015 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit http://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit http://www.usgs.gov/pubprod/. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. 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) iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Purpose and Scope ..............................................................................................................................3 Methods..................................................................................................................................................3 Study Area Description ........................................................................................................................5 Previous Studies ...................................................................................................................................5 Constructing Water-Surface Profiles .........................................................................................................5 Hydrologic and Steady-Flow Data .....................................................................................................5 Topographic/Bathymetric Data ..........................................................................................................5 Energy Loss Factors .............................................................................................................................6 Model Calibration and Performance .................................................................................................6 Development of Water-Surface Profiles ...........................................................................................7 Inundation Mapping ......................................................................................................................................8 Big Creek, Georgia, Flood-Inundation Maps on the Internet ........................................................8 Disclaimer for Flood-Inundation Maps .............................................................................................8 Uncertainties and Limitations Regarding Use of Flood-Inundation Maps ..................................8 Summary........................................................................................................................................................10 References Cited..........................................................................................................................................10 Figures 1. The study reach for Big Creek, U.S. Geological Survey streamgages, and National Weather Service forecast sites .................................................................................2 2. Big Creek bridge crossings, model extent, direction of surface-water flow, U.S. Geological Survey streamgages, and National Weather Service forecast sites ..............4 Tables 1. Site information for the U.S. Geological Survey streamgages in the Big Creek basin at Alpharetta and Roswell, Georgia .............................................................3 2. Comparison of hydraulic-model output and water-surface elevation at the Big Creek near Alpharetta, Georgia, streamgage ........................................................7 3. Stages (and water-surface elevations) with corresponding discharge estimates for selected simulated water-surface profiles at selected locations for the Big Creek near Alpharetta, Georgia, streamgage; and for the downstream boundary condition at Big Creek below Hog Waller Creek at Roswell, Georgia, streamgage ...............................................................................................9 4. Stream stages (and water-surface elevations) at the Big Creek near Alpharetta, Georgia, streamgage, with reference to corresponding map-sheet numbers in this report ..............................................................................................9 iv Sheets (Each sheet has individual pdf and jpg files available for downloading from http://dx.doi.org/10.3133/sim3338). 1–19. Maps showing flood-inundation of Big Creek in Alpharetta and Roswell, Georgia, corresponding to a gage height and an elevation (NAVD 88) as listed below at U.S. Geological Survey streamgage Big Creek near Alpharetta, Georgia (02335700) 1. Gage height of 6.0 feet and an elevation of 966.6 feet 2. Gage height of 6.5 feet and an elevation of 967.1 feet 3. Gage height of 7.0 feet and an elevation of 967.6 feet 4. Gage height of 7.5 feet and an elevation of 968.1 feet 5. Gage height of 8.0 feet and an elevation of 968.6 feet 6. Gage height of 8.5 feet and an elevation of 969.1 feet 7. Gage height of 9.0 feet and an elevation of 969.6 feet 8. Gage height of 9.5 feet and an elevation of 970.1 feet 9. Gage height of 10.0 feet and an elevation of 970.6 feet 10. Gage height of 10.5 feet and an elevation of 971.1 feet 11. Gage height of 11.0 feet and an elevation of 971.6 feet 12. Gage height of 11.5 feet and an elevation of 972.1 feet 13. Gage height of 12.0 feet and an elevation of 972.6 feet 14. Gage height of 12.5 feet and an elevation of 973.1 feet 15. Gage height of 13.0 feet and an elevation of 973.6 feet 16. Gage height of 13.5 feet and an elevation of 974.1 feet 17. Gage height of 14.0 feet and an elevation of 974.6 feet 18. Gage height of 14.5 feet and an elevation of 975.1 feet 19. Gage height of 15.0 feet and an elevation of 975.6 feet v Conversion Factors [Inch/Pound to International System of Units] Multiply By To obtain Length inch (in.) 25.4 millimeter (mm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) Area square foot (ft2) 0.09290 square meter (m2) square mile (mi2) 2.590 square kilometer (km2) Flow rate cubic foot per second (ft3/s) 0.02832 cubic meter per second (m3/s) Hydraulic gradient foot per mile (ft/mi) 0.1894 meter per kilometer (m/km) Datum Vertical coordinate information is referenced to the North American Vertical Datum of 1988 (NAVD 88). Horizontal coordinate information is referenced to the North American Datum of 1983 (NAD 83). Elevation, as used in this report, refers to distance above the vertical datum. Stage, as used in this report, is the height of the water surface above an arbitrary datum established at the gage (gage datum). Abbreviations AHPS Advanced Hydrologic Prediction Service DFIRM Digital Flood Insurance Rate Map FEMA Federal Emergency Management Agency GIS geographic information system lidar light detection and ranging NWS National Weather Service USGS U.S. Geological Survey vi Acknowledgments The author wishes to thank the cities of Alpharetta and Roswell, Georgia, for funding operation and maintenance of streamgages used for this study. Special thanks are given to the National Weather Service for their continued support to the U.S. Geological Survey flood-inundation mapping initiative. 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 Abstract the highest recorded water level at the Alpharetta streamgage site (15.0 feet). The simulated water-surface profiles were Digital flood-inundation maps for a 12.4-mile reach of then combined with a geographic information system digital Big Creek that extends from 260 feet above the McGinnis elevation model—derived from light detection and ranging Ferry Road bridge to the U.S. Geological Survey (USGS) data having a 3.0-foot horizontal resolution—to delineate the streamgage at Big