The purpose of this study is to introduce a modification of the Taylor and Schwarz method of synthesizing unit hydrographs whereby the Taylor and Schwarz equations may be used for urban watersheds. Brief reviews and discussions of the rational method, the Snyder method, and the Taylor and Schwarz method are presented. An investigation and discussion of the effect on the unit hydrograph of variations in Manning's coefficient of roughness, n, and the hydraulic radius, r, as caused by channel rectification is presented. The proposed method consists of determining the lag time of a hypothetical instantaneous unit hydrograph and computing a synthetic slope factor for the watershed. These parameters are substituted into the Taylor and Schwarz equations, and the unit hydrograph is computed. An example problem is included to demonstrate the procedure.