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• must be addressed. Disturbance from mining may impact all of these factors <br />except time and climate. The potential influences from the remaining five fac- <br />tors at the Trapper Mine need to be considered before formulating an effective <br />erosion control program. <br />Drainage characteristics are described in detail in section 2.7 of this applica- <br />tion. Briefly stated, the area is characterized by a series of south to north <br />parallel ephemeral and intermittent drainages with dendritic patterns. The drain- <br />ages are generally dip slope controlled, Several of the drainages have head cuts <br />and gullies that developed prior to any mining in the area. Towards the lower <br />ends, the drainages freouently have broad (5-20') and flat gullies with sharply <br />incised sides ranging a few to several feet in height. In such areas, Che bottoms <br />are typically heavily vegetated with grasses and occasional reeds and rushes. <br />The geology of the proposed mine plan area is discussed in detail in Sections <br />2.7.1.2 and 2.7.1.3. It can be generally described as being the south Elank of a <br />syncline with strata dipping north, northwest slightly steeper than the land sur- <br />face. The surficial strata primarily consist of coals, shales and sandstones <br />with the latter two being generally discontinuous. These have yielded soils of <br />moderate to high clay and silt content as discussed in Section 2.6. <br />The vegetation fur the proposed mine plan area is described in Section 2.3. IC <br />consists of big sagebrush and grasses on the lower and western areas that gradu- <br />a11y give way [o dense stands of mountain shrub on the upper and eastern areas. <br />Aerial plant cover has been recorded as ranging from less than 50% to nearly <br />100%. Schumm (1976) provided data from a small watershed in Utah showing that <br />erosion control from vegetative cover was imperceptible when cover was less than <br />10% and that very little additional control resulted as cover increased beyond <br />70%. <br />A detailed description of the hydrology of the proposed mine plan area is pro- <br />vided in Section 2.7. Approximately one-half of the precipitation received is in <br />the form of snow. This snow usually accumulates during Che winter months on [he <br />north facing slope where the proposed mine plan area is, yielding runoff from <br /> <br />3-57 <br />REVISED fE613 '87 <br />