Prepared in cooperation with the Virginia Department of Transportation Peak-Flow Characteristics of Virginia Streams Culpeper Basin WASHINGTON, D.C. MARYLAND WEST VIRGINIA Chesapeake Bay KENTUCKY ATLANTIC OCEAN TENNESSEE NORTH CAROLINA Scientific Investigations Report 2011–5144 U.S. Department of the Interior U.S. Geological Survey Cover art. See figure 1 (map showing peak-flow study sites in Virginia). Peak-Flow Characteristics of Virginia Streams By Samuel H. Austin, Jennifer L. Krstolic, and Ute Wiegand Prepared in cooperation with the Virginia Department of Transportation Scientific Investigations Report 2011–5144 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior KEN SALAZAR, Secretary U.S. Geological Survey Marcia K. McNutt, Director U.S. Geological Survey, Reston, Virginia: 2011 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 To order this and other USGS information products, visit http://store.usgs.gov Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this report is in the public domain, permission must be secured from the individual copyright owners to reproduce any copyrighted materials contained within this report. Suggested citation: Austin, S.H., Krstolic, J.L., and Wiegand, Ute, 2011, Peak-flow characteristics of Virginia streams: U.S. Geological Survey Scientific Investigations Report 2011–5144, 106 p. + 3 tables and 2 appendixes on CD. (Also available online at http://pubs.usgs.gov/sir/2011/5144/.) ISBN 978 1 4113 3288 1 iii Contents Abstract ...........................................................................................................................................................1 Introduction.....................................................................................................................................................1 Purpose and Scope ..............................................................................................................................1 Background............................................................................................................................................1 Physical Setting.....................................................................................................................................1 Coastal Plain .................................................................................................................................3 Piedmont........................................................................................................................................3 Blue Ridge .....................................................................................................................................3 Valley and Ridge ...........................................................................................................................4 Appalachian Plateaus .................................................................................................................4 Previous Studies ...................................................................................................................................4 Approach .........................................................................................................................................................4 Site Selection.........................................................................................................................................4 Data Evaluation .....................................................................................................................................8 Flood-Frequency Analysis ...................................................................................................................8 Basin Characteristics ...........................................................................................................................9 Regionalization .............................................................................................................................................10 Definition of Regions ..........................................................................................................................10 Model Development ...........................................................................................................................10 Model Verification and Diagnostics ................................................................................................11 Weighting Multiple Estimates ....................................................................................................................12 Weighting of Independent Estimates ..............................................................................................13 Peak-Flow Characteristics .........................................................................................................................13 Other Methods for Estimation at Ungaged Sites ....................................................................................13 Examples of Calculating Peak-Flow Estimates .......................................................................................14 Use of Regression Equations ............................................................................................................14 Drainage-Area Ratio Method ...........................................................................................................14 Ungaged Site with Nearby Gage ......................................................................................................15 Gaged Site ............................................................................................................................................15 Summary........................................................................................................................................................15 Acknowledgments .......................................................................................................................................16 References ....................................................................................................................................................16 Glossary .........................................................................................................................................................20 Appendix 1. Curves and residual plots for candidate single-parameter regional regression equations for estimating peak flows of streams in Virginia ..........................................................................................................CD in pocket Appendix 2. Curves and residual plots for candidate multi-parameter regional regression equations for estimating peak flows of streams in Virginia ..........................................................................................................CD in pocket iv Figures 1. Map showing selected peak-flow study sites and physiographic provinces for application of peak-flow regional estimating equations ..................................................2 2. Example leverage plots showing significant explanatory power, insignificant explanatory power, and evidence of collinearity ..................................................................11 Tables 1. Sites used in the study and their identifying information ..................................CD in pocket 2. Peak-flow characteristics of streamgaging stations in Virginia ........................................21 3. Regional regression equations for estimating peak flows of streams in Virginia .............5 4. Statistics summarizing basin characteristics selected for regional regression of peak flows in Virginia .........................................................................................CD in pocket 5. Selected basin characteristics, their definitions, and datasources ....................................6 6. Selected basin characteristics at peak-flow streamgaging stations in Virginia ..................................................................................................................CD in pocket Conversion Factors Inch/Pound to SI Multiply By To obtain Length inch (in.) 2.54 centimeter (cm) inch (in.) 25.4 millimeter (mm) foot (ft) 0.3048 meter (m) mile (mi) 1.609 kilometer (km) Area acre 0.4047 hectare (ha) square mile (mi2) 259.0 hectare (ha) Volume gallon (gal) 0.003785 cubic meter (m3) cubic foot (ft3) 0.02832 cubic meter (m3) acre-foot (acre-ft) 1,233 cubic meter (m3) 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) Vertical coordinate information is referenced to the North American Vertical Datum of 1929 (NAVD 29). 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. Peak-Flow Characteristics of Virginia Streams By Samuel H. Austin, Jennifer L. Krstolic, and Ute Wiegand Abstract landscapes. Peak-flow estimates provide a basis for analysis of future streamflow response to changes in ecosystem and Peak-flow annual