Prepared in cooperation with the Nebraska Department of Roads Peak-Flow Frequency Relations and Evaluation of the Peak-Flow Gaging Network in Nebraska Water-Resources Investigations Report 99–4032 U.S. Department of the Interior U.S. Geological Survey U.S. Department of the Interior U.S. Geological Survey Peak-Flow Frequency Relations and Evaluation of the Peak-Flow Gaging Network in Nebraska By Philip J. Soenksen, Lisa D. Miller, Jennifer B. Sharpe, and Jason R. Watton Water-Resources Investigations Report 99–4032 Prepared in cooperation with the Nebraska Department of Roads U.S. DEPARTMENT OF THE INTERIOR Bruce Babbitt, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government. Lincoln, Nebraska, 1999 For additional information write to: District Chief U.S. Geological Survey, WRD 406 Federal Building 100 Centennial Mall North Lincoln, NE 68506 Copies of this report can be purchased from: U.S. Geological Survey Branch of Information Services Box 25286 Denver, CO 80225 CONTENTS Page Abstract .............................................................................................................................................................. 1 Introduction ....................................................................................................................................................... 1 Background ......................................................................................................................................... 2 Purpose and Scope .............................................................................................................................. 2 Acknowledgments ............................................................................................................................... 4 Quantification of Drainage-Basin Characteristics ............................................................................................. 4 Morphometric Characteristics ............................................................................................................. 4 Soil Characteristics .............................................................................................................................. 5 Precipitation Characteristics ................................................................................................................ 5 Peak-Flow Frequency Analyses ........................................................................................................................ 5 Standard Analyses ............................................................................................................................... 6 Adjustments for Historic Data ....................................................................................................... 6 Adjustments for High and Low Outliers ....................................................................................... 6 Generalized Skew Coefficients............................................................................................. 7 High-Permeability Regional Skew Equation ....................................................................... 9 Northern and Western Regional Skew Equation ................................................................. 10 Northeastern Regional Skew Equation ................................................................................ 10 Southeastern Regional Skew Equation ................................................................................ 12 Low-Permeability Skew Map .............................................................................................. 12 Composite Analyses ............................................................................................................................ 12 Peak-Flow Frequency Relations ........................................................................................................................ 16 Unregulated Streams ........................................................................................................................... 16 Regional Equations ........................................................................................................................ 19 High Permeability Region ................................................................................................... 21 Northern and Western Region ............................................................................................. 23 Northeastern Region ............................................................................................................24 Central and South-Central Region ....................................................................................... 25 Eastern Region ..................................................................................................................... 26 Upper Republican River Region .......................................................................................... 27 Big Blue River Region ........................................................................................................ 28 Application of Equations ............................................................................................................... 28 Regulated Streams ............................................................................................................................... 29 Niobrara River ............................................................................................................................... 29 North Platte River .......................................................................................................................... 29 South Platte River .......................................................................................................................... 33 Platte River .................................................................................................................................... 33 Salt and Antelope Creeks .............................................................................................................. 33 Republican River ........................................................................................................................... 33 Frenchman Creek ........................................................................................................................... 38 Red Willow Creek ......................................................................................................................... 38 Network Evaluation ........................................................................................................................................... 41 Station Selection .................................................................................................................................. 41 Analyses and Output ........................................................................................................................... 41 Discussion of Results .......................................................................................................................... 44 Summary and Conclusions ................................................................................................................................ 44 Selected References ........................................................................................................................................... 46 CONTENTS iii CONTENTS--Continued Page Appendixes A—Descriptions of Selected Drainage-Basin Characteristics Quantified Using Basinsoft, ARC-INFO, and Related GIS Programs .............................................................................................A-1 Morphometric Characteristics ....................................................................................................... A-2 Modifications to Basinsoft .................................................................................................. A-2 Areal-Size Quantifications .................................................................................................. A-2 Linear-Size Quantifications ................................................................................................ A-2 Shape Quantifications ......................................................................................................... A-2 Relief Quantifications .........................................................................................................A-2 Aspect Quantification ......................................................................................................... A-3 Stream-Network Quantifications ........................................................................................ A-3 Relief-Stream Network Quantifications .............................................................................. A-3 Soil Characteristics ....................................................................................................................... A-3 Precipitation Characteristics ......................................................................................................... A-4 B—Tables of Drainage-Basin Characteristics and Peak-Flow Frequency Data ...................................... B-1 C—Graphs of Composite Peak-Flow Frequency Curves for Selected Stations ....................................... C-1 Figures