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Miguel River to the First Park area (Mercer, 1967). For a more historical discussion on the <br />Colorado Cooperative Company's development of the regional ditch system, the reader should <br />refer to Section 2.04.3 of the permit, Site Description and Land Use Information. <br />The West Lateral splits off the main ditch near the northern boundary of the Nucla Townsite. <br />The West Lateral follows a ridge -top course westward from Nucla through the New Horizon <br />Mine 2 area to the main north -south county road (2700 Road), then winds south and southwest <br />until the conveyed irrigation water is used by the various shareholders located along the ditch's <br />course. A total of 18 diversions were identified on this lateral; many consist of wooden "splitter <br />boxes" that divert a consistent proportion of the irrigation water from the lateral to fields via <br />small ditches and channels. Some diversions simply consist of pipes and hoses that also route <br />irrigation water to fields which are slightly lower in elevation. <br />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 .0 14 ft/ft <br />Flow in the West Lateral irrigation ditch is exclusively controlled by the Colorado Cooperative <br />Company. The ditch is "turned on" usually in mid - April, and continues to operate up until about <br />mid - October, depending on the length of each year's growing season and the availability of flow <br />in the San Miguel River. During the remainder of each year, the ditch is turned on temporarily to <br />provide water for filling cisterns and stock ponds. Water delivered via this lateral and the rest of <br />the surrounding ditch system provides a water source for irrigation, drinking water and livestock <br />use, and is the dominant seasonal influence of the hydrologic regime in the vicinity of the New <br />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 "flood- type" irrigation, travels laterally through the shallow <br />soils and fractured sandstone eventually flowing back into the West Lateral slightly downstream. <br />12 <br />