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The West Lateral irrigation ditch is an unlined open channel. Where the ditch courses along the <br />ridge top separating Tuttle Draw to the north and the Calamity Draw Valley to the south, the <br />ditch has been excavated through shallow soils into the highly fractured and weathered <br />sandstone. Over time, the ditch channel bottom has been subsequently scoured and eroded, <br />resulting in significant reaches of exposed and fractured sandstone. Further down the ditch <br />course, the ditch channel is constructed through deeper soils, and features a sandy channel <br />bottom. In most reaches, vegetation grows so heavily on the banks that the Colorado <br />Cooperative Company performs routine cutting and cleaning to ensure the integrity of the ditch <br />channel. Occasionally, where the ditch courses through the deeper soils, the ditch bottom is <br />periodically cleaned out (dredged). The overall gradient of the West Lateral irrigation ditch is <br />approximately .014 ft/ft <br />Flow in the West Lateral irrigation ditch is exclusively controlled by the Colorado Cooperative <br />Cvmpaiy. I1v ditch is "luiiled oil" usually in lllld-Api11, ails cG1IL1 ueS tG operate up until about <br />mid-October, depending on the length of each year's growing season. During the remainder of <br />each year, the ditch is turned on temporarily to provide water for filling cisterns and stock ponds. <br />Water delivered via this lateral and the rest of the surrounding ditch system provides a water <br />source for irrigation, drinking water and livestock use, and is the dominant seasonal influence of <br />the hydrologic regime in the vicinity of the New Horizon Mine. <br />Most reaches along the West Lateral lose irrigation flow to diversions, evapotranspiration and, of <br />course, seepage. The reaches that showed a loss in flow had water being withdrawn along each <br />reach through diversions on the day the study was performed, as well as significant lengths of <br />heavily vegetated bank sides. Seepage of irrigation water occurs along the entire reach of the <br />West Lateral, probably occurring at higher rates and volumes along the "ridge-top" reach where <br />the ditch was excavated through the shallow soils into the highly fractured sandstone. <br />The two reaches where the ditch featured gains in flow are portions of the general "ridge-top" <br />segment of the West Lateral. The ditch channel bottom in this reach is largely fractured and <br />weathered sandstone, and likely results in relatively large amounts of seepage. This seepage, in <br />combination with localized intensive "flooding-type" irrigation, travels laterally through the <br />shallow soils and fractured sandstone eventually flowing back into the West Lateral slightly <br />downstream. The combination of fractured, weathered sandstone channel bottoms in the ditch <br />and localized "flood-type" irrigation along these two gaining reaches likely resulted in the <br />measured gains in flow. <br />Flows in Calamity Draw, which is roughly parallel to the southern boundary of Mine 2, generally <br />reflect local irrigation practices. Water from the West Lateral Ditch's return irrigation flow is its <br />primary source. Very little supplemental flow is derived from precipitation and snowmelt <br />runoff. In 1987, measured flow rates in Calamity Draw varied from 0.605 cfs in April to 13.4 cfs <br />in July. Flow in Calamity Draw varied from 1.04 to 2.06 cfs during the non-irrigation period. <br />Shallow ground water alluvial sources provide a large portion of this low flow period's water. <br />This ground water flow is related to local irrigation practices but is consolidated into a more <br />uniform and regular flow by the permeability of these near surface alluvial deposits. Sediment <br />Pond 007 for the New Horizon Mine 2 mining site will contribute water to the Calamity Draw <br />system. The drainage system at the Mine 2 site has been designed to provide adequate capacity <br />12