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I I 1. Report No. 2. Government Accession No. 3. Recipient'. Cotalog No. FHWA-RD-77-l58 4. Titl. and Subtitle S. Report Oat. Runoff Estimates for Small Rural Watersheds and October 1977 Development of a Sound Design Method 6. Performing Organlzotion Cod. Volume I Research Report 7. Author(s) 8, Performing Organization R.port No. Joel E. Fletcher,A. Leon Huber, Frank.W. Haws. and Calvin G. Clvde 9. Performing Organization Nome ond'A<lclrlltu 10. Work Unit Ho. Utah Water Research Laboratory FCP 35H3-012 Utah State University 11. Contract or Gront No. Logan, Utah 84322 DOT-FH-1l-7809 13. Type of Report and,Period Covered 12. Sponsoring Agency Name and Address . Federal Highway Administration U.S. Department of Transportation Final Report Wa~h1ngton, D.C. 20590 14. Sponsoring Agency Cod. 15. SUPt:tlementory Noto. , FHWA Contract Manager: Frank K. Stovicek t 6. ,Abstract Potter's method for runoff peak forecasting was examined on its original watersheds and it was found to be soundly conceived. The method was modified to extend it to other watersheds in the same States for which it was originally developed. The results after modifying Potter's C parameter were found to be satisfactory. The method was simplified and extended to all of the contiguous United States, Alaska, Hawaii, and Puerto Rico. After beginning with a 7-parameter method, it was found that 3-parameters, namely area, rainfall erosivity factor and difference in elevation from top to bottom of the watershed produced peak flow estimates of vir- tually equal reliability. The standard error of estimates of the ten year peak flow as computed by the different equations for a random sample of 51 watersheds from throughout the United States and Puerto Rico were: 39 percent for the 3-parameter all zone, 62 percent for 7-parameter all zone, 50 percent for 3-parameter zone, and 38 percent for 7-parameter zone equations. Consequently the three parameter equa- tions were selected for design purposes and nomographs for solving the equations were developed for each hydrophysiographic zone 'of the United States and Puerto Rico. The other volumes of this report are: FHWA-RD- Subtitle 77-159 Vol II Recommendations for preparing design manuals and Apps B, C, D, E, F, and H 77-160 Vol III App A "Data and Frequency Curves" 17, K.. W.rds H d 1 small watersheds, 18. Distribution Statement This document is availab~ y ro ogy, .hydrophysiographic zones, peak runoff, to the public through the National Techni- flood frequency, regression analysis, cal Information Service, Springfield, graphical correlation, estimating Virginia 22161- discharge, design, nQmographs. 19. Security Clossil, (of this report) 20. Security Clossif. (of thi s page) 21. No. of Pagu 22. Price , Unclassified 120 Uncia , TECHNICAL REPORT STANDARD TITLE PAGE Fo,m DOT F 1700.7 (....) L