Laserfiche WebLink
I• <br />• <br />r1 <br />LJ <br />snowmelt during April, May and June. According to Miller, at al. (1973), 1.7" of precipitation over 24 hours was <br />equal to a ten year, 24 hour precipitation event for the area. Subsequent determinations by the National <br />Oceanographic and Atmospheric Administration (NOAA) defined the 10-year, 24 hour rainfall event as 1.4" <br />and the 25-year, 24 hour rainfall event as 1.8". Trapper formally adopted these values with the approval of the <br />ZDivision during the 1992 RN-02 renewal application process. <br />Land use is discussed in Section 2.5. The area has been historically used for grazing sheep and cattle and for <br />dryland farming of winter wheat. Substantial areas have been put into cropland on slopes considered too <br />steep (>12%) by the U.S. Soil Conservation Service (1975). Contour farming has not been commonly <br />practiced and small ephemeral drainages are frequently tilled and seeded. Typically, all croplands are <br />mechanical (allowed every other year, resulting in barren fields about 75% of the time. <br />There is very little that can be done to influence the climate or the soils of the area, but both vegetation and <br />land management practices can be planned to minimize erosion on disturbed areas. Land management <br />practices can be further categorized as interim and long-term. Interim measures are those used initially, <br />mostly mechanical, to control erosion while perennial vegetation is establishing. Such practices may include <br />contour furrowing, land imprinting, deep ripping, chisel plowing, pitting or any other form of surface <br />manipulation to interrupt air and water flow and improve moisture retention and infiltration on site. All or <br />combinations of these various treatments are used to control erosion of retopsoiled areas at Trapper Mine. <br />Where necessary, more intensive controls as described in Sections 3.6.2.5 and 3.6.3.6 will be employed. <br />In all instances, the primary effort at Trapper Mine will be directed towards preventing channelization of runoff <br />and maximizing retention and infiltration on site. Where channelizing unavoidably occurs, efforts will be <br />directed towards achieving a channel that is stable. <br />3-58 <br />?j