Surface-water quality and flow Modeling Interest Group
1 U.S. Geological Survey, Urbana, IL
2 Marquette University, Milwaukee, WI
3 Reitz & Jens Inc., St. Louis, MO
For more information, please contact:
Timothy D. Straub
U.S. Geological Survey
221 North Broadway Avenue
Urbana, IL 61801
Internet: tdstraub@usgs.gov
Phone: (217) 344-0037x3024
FAX: (217) 344-0082
Printed copies may be obtained by contacting
U.S. Geological Survey
Branch of Information Services
Box 25286
Denver, CO 80225-0286
The printed copy of this report includes a CD-ROM containing the rainfall
and runoff data, HEC-1 input files and a digital copy of this report.
Citation:
Straub, T.D., Melching, C.S., and Kocher, K.E., 2000, Equations for estimating
Clark unit-hydrograph parameters for small rural watersheds in Illinois:
U.S. Geological Survey Water-Resources Investigations Report 00-4184, 30 p.
The rainfall and runoff data from gaged small rural watersheds (0.02-2.3 mi2) with insignificant amounts of impervious land cover in Illinois were used to develop the equations. Equations were developed on the basis of data for 121 storms that occurred in 39 watersheds. Data for 29 storms in 18 watersheds were used to verify the equations.
TC and R were determined by calibrating available rainfall and runoff data, using the U.S. Army Corps of Engineers Flood Hydrograph Package HEC-1. The mathematical relations between watershed and storm characteristics, and TC and R were determined by multiple-linear regression of the logarithms of the values. Main-channel length and slope were identified as important watershed characteristics for estimating TC and R. The estimation equations had coefficients of determination of 0.73 and 0.64 for the logarithms of TC and R, respectively. When storm characteristics were added in the regression of hydrograph parameters utilizing length and slope, only minimal increases to the coefficient of determination resulted. Thus, storm characteristics were not considered further in development of the equations.
Simulation of the measured discharge hydrographs for the verification storms utilizing TC and R obtained from the estimation equations yielded good results. The error in peak discharge for 21 of the 29 verification storms was less than 25 percent, and the error in time-to-peak discharge for 18 of the 29 verification storms also was less than 25 percent. Therefore, applying the estimation equations to determine TC and R for design-storm simulation may result in reliable design hydrographs, as long as the physical characteristics of the watersheds under consideration are within the range of those characteristics for the watersheds in this study [area: 0.02-2.3 mi2, main-channel length: 0.17-3.4 miles, main-channel slope: 10.5-229 feet per mile, and insignificant percentage of impervious cover].
Download the complete report [PDF, 914 Kb].
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