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<br />39 <br /> <br /> <br />U018,,0 <br /> <br />shown in figure 1. Figurj!! 1, which was developed by, the S.oil Con- <br /> <br />servation S.ervice, is reasonably, accurate when the bulk of the <br /> <br />annual yield results from surface runoH derived Jrom rainstorms, <br /> <br />It does not give acceptable results in areas where' runoff is derived <br /> <br />from snowmelt. <br /> <br />Extr<Lpolation beyond the area limits of the nomogr<l:ph should <br /> <br />not be made as these relationships _were derived from s'mall water- <br /> <br />. <br /> <br />shed areas. The graph on"the right-hand side of the figure relating <br /> <br />annual yield to percent chance of oC,currence is independent of the <br /> <br />remainder of the nomograph and can be ~sed to estimate the prob- <br />/ <br />ability of obtaining ,a given supply a certain percent of the year. <br /> <br />For example, if the average annual supply is estimated to be 1 <br /> <br />inch of runoff, 7 years out of 10 at least 0.2.6 of an inch ofrunof~_// <br />// <br />can be expected and 9 years out of 10 at lea~t,O.l of an inch or' <br /> <br />. runoH can be expected. <br />