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<br />By making the necessary correction to the USGS areas, all the TC&B areas matched <br />the USGS gage areas within 3 percent. Therefore, the TC&B drainage areas were <br />used because they are based on a more current source of information, were computed <br />digitally, and have been defined at points along the study streams where flows are <br />needed. <br /> <br />Peak discharge-drainage area relationships for Burgess Creek, Elk River, Walton <br />Creek, and Yampa River are shown in Table 1. <br /> <br />Butcherknife.. Fish.. Soda.. and Spring Creeks <br /> <br />The analyses were based on rainfall-runoff computations and statistical analysis of <br />stage and discharge records by the log-Pearson Type III method (Reference 10), with <br />modifications for the standard project and other rare flood events. The USACE <br />standard project rainfall and flood concept and the unit hydrograph method of <br />analysis were used in making rainfall-runoff computations. Snowmelt flood data <br />were derived from analysis of snowmelt flow records for the Yampa River. The <br />general mountain S-graph for Arizona, Colorado, Utah, and Wyoming was used to <br />produce unit hydrographs for the studied creeks. <br /> <br />As noted earlier, general rainstorms that generate major floods in western Colorado <br />usually occur during September and October. On the basis of available precipitation <br />records, a standard project storm for the Yampa River Basin was developed using a <br />flood-producing storm that occurred in September 1970 in the Four Corners area (the <br />area of the intersection of Arizona, New Mexico, Utah, and Colorado) as a model. <br />The Steamboat Springs regional 24-hour probable maximum precipitation is very <br />similar to that of the San Juan Mountains and the Grand Mesa area (Reference 16). <br />Therefore, a standard project storm centered over the Grand Mesa area east of the <br />City of Grand Junction was developed and transposed to locations on the White River <br />Plateau and the Park Range. This produced a 40-hour storm with a 3.35-inch rainfall <br />over the Yampa River drainage above Agate Creek and a 4. 13-inch average rainfall <br />on the Park Range. <br /> <br />Loss rates for the basin were estimated because of lack of reproducible rainfloods in <br />the area. Study of runoff in the Grand Mesa area during the 1970 Four Comers <br />storm indicated high (greater than 1.5 inches) initial losses. A study of streamflow <br />and precipitation data published by the USFS (Reference 17), for subalpine <br />watersheds (including West Walton, North Fish, and Soda Creeks) indicates that <br />approximately 2.0 inches of rain must fall in the August to October period for <br />appreciable runoff to occur. Loss rates selected for the 100- and 500-year general <br />rainfloods were 2.00 inches of initial loss and 0.15 inch per hour constant loss. <br /> <br />Little definitive data on cloudburst flood events are available for the Steamboat Springs <br />area. The June 1921 flood may have been the result of a cloudburst that augmented <br />abnormal snowmelt runoff. Contributing rainfall totaled more than 2.5 inches, but the <br />period of time in which the rain fell is not definitely known. A newspaper account <br />indicated that it may have been between 12 and 20 hours. However, 2.04 inches of rain <br />in 3 hours and a 24-hour rainfall of 3.24 inches have been recorded in the region. <br /> <br />26 <br />