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• <br />However, consistent with best management practices, if the access stem <br />is properly designed, laid out, and drained, the intercepted water should <br />be distributed back over the basin surface and allowed to re-infiltrate <br />into the soil mantle if storage is available. phis minimizes the impact <br />on the hydrograph to the point where the true effect of the access <br />system per se, is questionable and certainly beyond the state-of-the-art <br />to predict as part of this exercise. <br />The most significant impact that mining activities can have on storm <br />flow is through their modification of antecedent storage. As the <br />intensity of disturbance increases, the deficit or storage capacity at <br />any point in time, decreases. With less storage capacity, more of the <br />precipitation appears as stormflow. <br />There are many techniques for estimating storm runoff. for the <br />~~• <br />purposes of this report, one technique has been used, not because it is <br />necessarily the best, but because it is universal in application. The <br />"SCS method" is one of the more widely used techniques and principles <br />of the method are surtQnarized here since: (1) it is applicable to <br />ungaged watersheds, where at best, rainfall data are available on a <br />daily basis from non-recording gages, and (2) it is a standard and <br />recognized engineering approach for predicting storm runoff (U.S. Soil <br />Conservation Service, 1972). <br />It should be emphasized that if the method is used to determine <br />hydrologic impacts from mining activities, care should be taken to <br />relate the rainfall/runoff relationships to processes insofar as possible. <br />I• <br />