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• (square miles) is an important indicator of the basin texture. Figure 2.7-181 is a plot of drainage <br />density versus basin slope defined as: <br />total length of 100' contours (feet) x contour interval (feet) <br />basin area (square feet) <br />The two dashed lines on the plot indicate the envelope into which the scatter fits. Tha plot shows <br />a lot of scatter indicating that drinage density in the Trapper area is dependent on more than <br />one variable. Drainage density is dependent on Gimate, vegetation, geology, age of basin and <br />basin slope. Basin slope, vegetation and age of the basins are not considered to be constant <br />within this region. The figure does indicate, however, that drainage density increases as basin <br />slope increases. This is consistent with other studies (Schumm, 1977). The drainage densities <br />given in Table 2.7-12b represent the sub-basins within the mine property. These values are <br />higher than those given in Table 2.7-19 which were obtained for the entire basin from a USGS 1' <br />= 2000' map. <br />The average slope of the main channel was examined for the eight basins. The sbpe varied <br />between .088 and .11. Longtudinal profiles through the mine plan area for the longest channel in <br />• the sub-basins which make up Flume and Pyeatt Gulches have been plotted on Figures 2.7-18j <br />through 2.7-180. Longitudinal drainage profiles are also given in Map M74, with watersheds <br />illustrated on Map M51. The profiles again show a typical decease in gradient in the downstream <br />direction. Within the profiles, there are reaches where the gradient is steeper. These reaches <br />are similar to other channels in the mine permit area mentioned previously where the streams are <br />lowering their gradients naturely by headcutting in the steeper reaches. This is occurting in both <br />alluvial <br />J <br />2~54b <br />-_ PR-~I <br />;: ; ;..`JIAY 1 3 199$ <br />