U.S. Department of the Interior U.S. Geological Survey Estimating the Magnitude of Peak Flows for Streams in Kentucky for Selected Recurrence Intervals By Glenn A. Hodgkins and Gary R. Martin Water-Resources Investigations Report 03-4180 In cooperation with the Kentucky Transportation Cabinet, Department of Highways Louisville, Kentucky 2003 U.S. DEPARTMENT OF THE INTERIOR GALE A. NORTON, Secretary U.S. GEOLOGICAL SURVEY Charles G. Groat, Director Any use of trade, product, or firm names is for descriptive purposes only and does not imply endorsement by the U.S. Government. For additional information contact: Copies of this report can be purchased from: District Chief, Kentucky District U.S. Geological Survey U.S. Geological Survey Information Services 9818 Bluegrass Parkway Box 25286 Louisville, KY 40299–1906 Denver, CO 80225–0286 http://ky.water.usgs.gov CONTENTS Abstract............................................................................................................................................................ 1 Introduction...................................................................................................................................................... 1 Description of study area................................................................................................................................. 2 Climate.................................................................................................................................................... 2 Physiography and geology...................................................................................................................... 4 Seasonality of peak flows ....................................................................................................................... 4 Data used for peak-flow estimates and estimating techniques ........................................................................ 8 Development of peak-flow estimates and estimating techniques....................................................................10 Peak flows at gaging stations.................................................................................................................. 10 Detailed Bulletin 17B analyses ..................................................................................................... 10 Generalized skew for Kentucky..................................................................................................... 11 Peak flows at ungaged locations............................................................................................................. 12 Defining flood regions................................................................................................................... 13 Choosing explanatory variables..................................................................................................... 14 Determining final regression coefficients...................................................................................... 17 Weighting gaging-station peak-flow estimates with regression-equation peak-flow estimates ............. 18 Estimating the magnitude of peak flows for selected recurrence intervals ..................................................... 18 Choosing the appropriate peak-flow estimation technique .................................................................... 18 Estimates of peak flows at U.S. Geological Survey streamflow-gaging stations................................... 19 Presentation of the estimates ......................................................................................................... 19 Limitations and accuracy of the estimates..................................................................................... 21 Estimating peak flows for ungaged sites on regulated streams or streams with diversions ................... 21 Estimating peak flows for ungaged, unregulated streams in urbanized drainage basins........................ 21 Estimating peak flows for ungaged sites on gaged, unregulated streams in rural drainage basins ........ 22 Application of the technique ......................................................................................................... 22 Limitations of the technique.......................................................................................................... 25 Estimating peak flows for ungaged, unregulated streams in rural drainage basins................................ 25 Application of the technique ......................................................................................................... 25 Limitations and accuracy of the technique.................................................................................... 26 Example applications of the estimating equations ................................................................................. 27 Summary.......................................................................................................................................................... 29 References cited............................................................................................................................................... 29 PLATE 1. Locations of Kentucky hydrologic region boundaries and streamflow-gaging stations used in the study............................................................................................................... (in pocket on inside back cover) Contents iii FIGURES 1–4. Maps showing: 1. Major drainage basins in Kentucky........................................................................................... 3 2. Shaded-relief image of landforms in Kentucky......................................................................... 5 3. Physiographic regions in Kentucky........................................................................................... 6 4. Generalized carbonate areas and surficial karst development in Kentucky .............................. 7 5. Flowchart for choosing the appropriate means of obtaining estimated peak flows in Kentucky .... 20 6. Graph of total drainage area and main-channel slope sampling spaces for the peak-flow regression equations for Regions 1 and 4 in Kentucky.................................................................... 23 TABLES 1. Estimated peak flows for 222 selected U.S. Geological Survey streamflow-gaging stations in Kentucky ....................................................................................................................................... 33 2. Total drainage areas and main-channel slopes for 238 streamflow-gaging stations used to develop the peak-flow regression equations for Kentucky ................................................................ 61 3. Regression equations and their accuracy for estimating peak flows for ungaged, unregulated streams in rural drainage basins in Kentucky..................................................................................... 15 4. Range in values of the basin characteristics used as explanatory variables in the regional peak-flow regression equations for Kentucky.................................................................................... 22 5. Coefficients (exponents) of the drainage-area-only regional peak-flow regression equations for Kentucky....................................................................................................................................... 24 CONVERSION FACTORS Multiply By To obtain inch (in.) 25.4 millimeter inch per hour (in/h) 0.0254 meter per hour foot (ft) 0.3048 meter foot per mile (ft/mi) 0.1894 meter per kilometer cubic foot (ft3) 0.02832 cubic meter cubic foot per second (ft3) 0.02832 cubic meter per second mile (mi) 1.606 kilometers square mile (mi2) 2.590 square kilometer Temperature in degrees Fahrenheit (°F) may be converted to degrees Celsius (°C) as follows: °C = (°F - 32) / 1.8 iv Contents Estimating the Magnitude of Peak Flows for Streams in Kentucky for Selected Recurrence Intervals By Glenn A. Hodgkins and Gary R. Martin Abstract One section of this report describes techniques for estimating peak flows for This report gives estimates of, and ungaged sites on gaged, unregulated streams in presents techniques for estimating, the rural drainage basins. Another section magnitude of peak flows for streams in references two previous U.S. Geological Survey Kentucky for recurrence intervals of 2, 5, 10, 25, reports for peak-flow estimates on ungaged, 50, 100, 200, and 500 years. A flowchart in this unregulated, urban streams. Estimating peak report guides the user to the appropriate flows at ungaged sites on regulated streams is estimates and (or) estimating techniques for a beyond the scope of this report, because peak site on a specific stream. flows on regulated streams are dependent upon Estimates of peak flows are given for 222 variable human activities. U.S. Geological Survey streamflow-gaging stations in Kentucky. In the development of the peak-flow estimates at gaging stations, a new INTRODUCTION generalized skew coefficient was calculated for the State. This single statewide value of 0.011 Estimates of the magnitude of peak (with a standard error of prediction of 0.520) is streamflows (such as the 50-year-recurrence- more appropriate for Kentucky than the national interval peak flow) are necessary to safely and skew isoline map in Bulletin 17B of the economically design bridges, culverts, and other Interagency Advisory Committee on Water structures that are in or near streams.