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Summary <br />It is recommended th at flows of Q = 565-cfs, Q = 680-cfs <br />10 25 <br />and Q = 820-cfs can be used in evaluating effects of the Apex <br />100-' <br />Mine #2 fill area on Trout Creek. The fill area causes a constrir <br />tion of the flood plain that results in depth and velocity increases <br />through the constriction. Some additional bank protection may be <br />needed through the constriction by reworking the material already <br />in place or importing riprap material to resist erosion. The <br />velocities created by the constriction are not unusual for this <br />stream and the effects are confined to the fill area and the land <br />300-400' upstream and downstream from the fill area. Some channel <br />erosion may occur in and around the constriction but it will be <br />isolated. <br />SITE DRAINAGE <br />Hydrology <br />Effective precipitation resulting from a rainfall event with <br />a return frequency of 10 years and 25 years has been calculated <br />based on the procedure recommended by the Soil Conservation Service <br />previously cited. The hydrologic soil group D has been used, <br />both as being most representative of the local soils and area <br />usage, and as being most conservative. Table 2-2 of 'Drban <br />Hydrology for Small Watersheds', Soil Conservation Service,. Dept.. <br />of Agriculture, published in January 1975, recommends the following <br />curve numbers for Soil Group D. ~ , <br />i <br /> <br />.~ <br />I'~' <br />