Rainfall and runoff data from urbanized drainage basins in the Wichita area, Kansas, were used to evaluate the Soil Conservation Service synthetichydrograph method of computing flood hydrographsfrom rainfall data. The method was tested on six basins where the impervious surface ranged from 11 percent on the least urbanized basin to 40 percent on the most urbanized. Twenty-two of the largest storm events for which peak discharges had been observed were used in the test. After modification of the method for this particular area, results showed an average error of 20 percent, disregarding sign, with an apparent bias of 8 percent. However, uncertainties in some of the data make it impractical to adjust for bias.
Application of the modified method using data on rainfall, impervious surface, soils, land use, channel slope, length of main channel, and drainage area is described for a hypothetical basin. As an alternative to more complete and complex modeling by digital computer, a peak discharge for drainage design can be calculated by applying the SCS method to a standardized "design storm" for a specified recurrence interval. The method is sensitive to soil conditions and land use; therefore, accurate information on these factors is necessary.
