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I <br />~. <br />`~, <br />1~ <br />ll~~~~\ ~ - c.• - ~ .Z <br />PROBABLE HYDROLOGIC CONSEQUENCES OF MINING OPERATION <br />Surface Water <br />The Bourg property is located on Mann Draw, a left bank <br />tributary of the Canadian River (see Figure 1). Mann Draw is <br />intermittent with flows normally occurring only during the <br />spring runoff season. During the rest of the year, flow <br />occurs only in response to heavy rainfall events. The <br />drainage area at the Bourg site is 2.35 square miles, and at <br />the confluence with the Canadian River is 3.39 square miles. <br />The average annual runoff from the Mann Draw watershed was <br />estimated using a U.S.G.S. gauge on a similar draw in the <br />Canadian River Basin. The gauge is located on Williams Draw, <br />also a left bank tributary of the Canadian, located <br />approximately 4 miles southeast of the Bourg site. Runoff <br />records are available for only one complete season, 1980. <br />There are no other gauges in the vicinity located on a <br />hydrologically similar watershed. To approximate the average <br />annual runoff, the runoff in 1980 was adjusted using long- <br />term average precipitation at the Walden Climatological <br />Station, located 8 miles from the gauge. The adjusted unit <br />runoff for Williams Draw was .047 acre-feet/acre. Applying <br />this value to the Mann Draw Basin resulted in the following <br />average annual runoff values. <br />Tributary Average <br />Ares Annual Runoff <br />Site (mi ) (acre-feet) <br />Mann Draw at mouth 3.39 100 <br />Mann Draw at <br />Bourg Mine 2.35 69 <br />Bourg Mine Area 0.47 14 <br />Leonard Rice Consulfirg Waler Engineers. Inc. <br />I-36 <br /> <br />