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• 8 <br />2.3.1 Runoff Due to Rainfall <br />Two methods were used to estimate the runoff due to a rainfall event. The <br />first method uses regression equations rhieh relate llood characteristics to <br />measurable basin and climate parameters for ungauged sites. Ths regression <br />1 equation is given in the 'Manual for Estimating Flood Characteristics for <br />Natural-Flow streams in Colorado, Technical Manual 1' (TM-1). The TM-1 manual <br />gives equations for peak discharges based on effective drainage area (AE) and <br />basin slope (S$) for the 10-. 50-, 100-, and 500-year return frequencies. To <br />(. obtain the 2- and 25-year peak discharges, a logarithmic-probability plot o! <br />l the 10-, 50-, 100-, and 500-year events was made and the graph used to estimate <br />r <br />the 2- and 25-year peak discharges. The 2-, 10-, 25-, and 100-year peak dis- <br />charges for Magpie, Newlin and the Tipple area drainages are given in Sable 1. <br />A subscript to the table gives the equations used and the area and basin slope <br />used for each drainage area. The data used for development of the equations <br />presented in TM-1 vas from drainage basins with much larger areas than the drain- <br />age areas being studied. Through our experience with small watersheds, TM-1 <br />tends to give a high estimate of the peak discharge fmm small watersheds. <br />The aernnd method used to estimate the peak discharge employs regression <br />equations developed for small rural watersheds in the Arkansas River basin of <br />Colorado. The development and use of the equations are given in 'Rainfall-Runoff <br />Modeling and preliminary Regional Flood Characteristics of small Rural Watersheds <br />in the Arkansas River easin•in Colorado.' A network of 17 runoff gauging stations <br />was used to evaluate the magnitude and frequency of flood discharges and wlumes. <br />The regional relationships were developed by combining and weighting statistical <br />analysis of the recorded data with a long-term synthetic annual flood series <br />. Fro3uced by a rainfall-runoff model. The regional relationships are given as <br />regression equations relating peak discharge to drainage basin area and relating <br />{ <br />