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<br />00312l <br /> <br />Page 20 <br /> <br />(I) Annual precipitation for the treatment area on the Arapaho National <br /> <br />Forest was estimated for each of the 72 years of reconstructed flow for the <br /> <br />Colorado River at Glenwood Springs. This was accomplished with a <br /> <br />precipitation-runoff relationship developed from data for St. Louis Creek on <br /> <br />the Fraser Experimental Forest. St. Louis Creek is a typical site within the <br /> <br />study area and offers the best set of comparable precipitation and runoff <br /> <br />data. These data yielded the following relationship of annual precipitation <br />2 <br />(P) to annual runoff (RO) (n=17, R =0.45, standard error=2.77, <br /> <br />significance=0.002): <br /> <br />P = 9.72 + 1.19 RO. <br /> <br />Annual precipitation of the treatment sites was estimated from this <br /> <br />relationship under assumption (1) that St. Louis Creek was representative <br /> <br /> <br />the treatment area as a whole and (2) that annual runoff at St. Louis Creek <br /> <br />was proportional to annual flow on the Colorado River at Glenwood Springs. <br /> <br />Proportionality was specified in relation to mean annual flow, which was <br /> <br />1,442,000 acre feet for the 72 years of data from the Colorado River at <br /> <br />Glenwood Springs and 15 inches for the 37 years of runoff data from St. Louis <br /> <br />Creek. (Note that annual runoff at St. Louis Creek also averaged 17 inches <br /> <br />for the 17 years for which precipitation records were available.) For <br /> <br />example, annual flow on the Colorado River at Glenwood Springs was 2,286,170 <br /> <br />acre feet in 1912, or 1.556 times mean annual flow. Thus, annual runoff from <br /> <br />St. Louis Creek was assumed to be 1.56 times mean annual flow on St. Louis <br /> <br />Creek. Such a year would, via the precipitation runoff relationship, be <br /> <br />assumed to experience an annual precipitation of 9.72+(1.19)(15)(1.56) = 37.5 <br />/ <br />inches. Table 111-1 lists predicted annual precipitation (Column 2) for the <br /> <br />l <br />~ <br /> <br />I <br />