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. ,. <br />Page 2 <br />• 2. Relative elevation 'y', the ratio of elevation at a specific <br />contour, h, to total basin relief, H (elevation at downstream <br />reference point -elevation at basin divide), is calculated <br />for successive contours and tahulated. <br />3. Relative area 'x', the ratio of horizontal cross-sectional <br />area at successive contours to total drainage area at the <br />downstream reference point, is calculated and tabulated. <br />4. On arithmetic paper x (ordinate) and y (abcissa) are plotted. <br />The points are connected to form a continuous function. <br />B. Surface slope distribution <br />Fre- and post-mining slope distribution maps are formed for the <br />affected area as Follows (Straiil.er, 1952, 1964): <br />1. A 100 x 100 grid square pattern per section (640 acres) is <br />overlain on the topographic map. <br />2. Tlic maximum slope tangent (rise over run) is determined at each <br />grid intersection. NOTE: tangent x 100 = percent slope. <br />3. The tangent values are contoured coith lines through point of <br />• equal value (isotangents). Tangent contour increments should <br />be 0.05 (5 percent slope). <br />4. The areas between successive tangent contours are planimetered <br />and summed for each slope class. <br />5. A histogram of slope frequency (abcissa) vs. slope class <br />(ordinate) is constructed.and"the mean and variance of this <br />distribution are computed. ~ <br />6. The map, histogram and statistics should be presented. <br />NOTE: The above method can he-done by band. Computer methods are <br />available and ;acceptable. <br />Rnf rranrFc <br />S[rahler, A.N., 1964, Quantitative geomorphology of drainage basins and <br />channel neCworks, In V.T. Chow (ed.) Handbook of Applied Hydrology, <br />McCraw }lill IIook Company, San Francisco, pp. 4-39 to 4-7G. <br />SCral~lcr, A.N., 1952, llypsometric (area-altitude) analysis of erosional <br />topography, Bulletin of Geological Society of America, l'ol. 63, <br />pp. ]11)-1142. <br /> <br />