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<br />Step 1 - Log-Pearson Calculations from on-stream gauging station <br />Flood flows for the 2 streams for 10, 50, 10D-and 50D-year recurrence <br />intervals were obtained from reference no. 2 and no. 3 In the <br />2 references, peak flows have been calculated from a statistical analysis <br />of annual series data using the Log-Pearson Type III distribution, as <br />recommended by the Water Resources Council (reference no. 1 ). <br />Step 2 - Regional curve for selected area stream <br />A minimum of 10 years of record is recommended when the standard Log- <br />Pearson Type III method is used. To verify the calculated peak flows for <br />Henson Creek and the Lake Fork, a regional curve was prepared using peak <br />flows calculated from streamflow data for 19 additional gauging stations <br />within basins in the San Juan Mountains and the Gunnison area. Basins <br />were selected for comparison on the basis of similar elevations, drainage <br />area, precipitation and topographic characteristics. According to CWCB <br />Technical Manual No.1, high mountain basins west of the Continental <br />~ivide in the San Juan Mountains are subject to infrequent high intensity <br />rainfalls which may cause peak flows similar to that caused by runoff. <br />This fact was considered in preparing the regional curve. Peak flows for <br />each station were plotted versus drainage area on log-log paper as <br />suggested by Linsley (reference no. 4 ). <br /> <br />Step 3 - Regression Equations for Mountain Region <br />As a further check on our calculations, peak flows were calculated <br />using regression equations recommended by CWCB Technical Manual No. 1 <br />(reference no. ~). The regression equations represent regional <br />curves for the entire mountain region of Colorado. However, they are <br />site specific in that they require input of precipitation and drainage <br />areas applicable to the study area. <br /> <br />Several other hydrological methods were considered, but not used for <br />various reasons. The Soil Conservation Service rainfall-runoff methods <br />generally produce fairly accurate results. However, they require <br />relatively involved data collection and calculations, a procedure that <br />was beyond the scope (budget) of this study. The only other potentfally <br />applicable method was discussed in Reference No. 1 (comparison with <br />a similar water shed that may have a long period of records). However, <br />this method has an accuracy equivalent to that of analysis of a 10 year <br />station record (which was available on Lake Fork and Henson Creeks). <br />