2018-04-06_GENERAL DOCUMENTS - C1981008

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that originates on the San Miguel River just upstream of Cottonwood Canyon (about 12 miles upstream of Naturita). Construction of the main ditch commenced in 1896, and water began flowing to the First Park area via the ditch in the spring of 1904 (Mercer, 1967). The main ditch, as well as the main laterals, is basically an unlined open channel excavated in shallow soils and sandstone. Where the ditch crosses drainages, pipes and aqueducts have been constructed to carry the flow. The main ditch has an average gravity run of four feet per mile from the San Miguel River to the First Park area (Mercer, 1967). For a more historical discussion on the Colorado Cooperative Company's development of the regional ditch system, the reader should refer to Section 2.04.3 of the permit, Site Description and Land Use Information. The West Lateral splits off the main ditch near the northern boundary of the Nucla town site. The West Lateral follows a ridge -top course westward from Nucla through the NHM area to the main north -south county road (2700 Road), then winds south and southwest until the conveyed irrigation water is used by the various shareholders located along the ditch's course. A total of 18 diversions were identified on this lateral; many consist of wooden "splitter boxes" that divert a consistent proportion of the irrigation water from the lateral to fields via small ditches and channels. Some diversions simply consist of pipes and hoses that also route irrigation water to fields which are slightly lower in elevation. The West Lateral irrigation ditch is an unlined open channel. Where the ditch courses along the ridge top separating Tuttle Draw to the north and the Calamity Draw Valley to the south, the ditch has been excavated through shallow soils into the highly fractured and weathered sandstone. Over time, the ditch channel bottom has been subsequently scoured and eroded, resulting in significant reaches of exposed and fractured sandstone. Further down the ditch course, the ditch channel is constructed through deeper soils, and features a sandy channel bottom. In most reaches, vegetation grows so heavily on the banks that the Colorado Cooperative Company performs routine cutting and cleaning to ensure the integrity of the ditch channel. Occasionally, where the ditch courses through the deeper soils, the ditch bottom is periodically cleaned out (dredged). The overall gradient of the West Lateral irrigation ditch is approximately .014 ft/ft Flow in the West Lateral irrigation ditch is exclusively controlled by the Colorado Cooperative Company. The ditch is "turned on" usually in mid-April, and continues to operate up until about mid-October, depending on the length of each year's growing season and the availability of flow in the San Miguel River. During the remainder of each year, the ditch is turned on temporarily to provide water for filling cisterns and stock ponds. Water delivered via this lateral and the rest of the surrounding ditch system provides a water source for irrigation, drinking water and livestock use, and is the dominant seasonal influence of the hydrologic regime in the vicinity of the NHM. Most reaches along the West Lateral lose irrigation flow to diversions, evapotranspiration and, of course, seepage. The reaches that showed a loss in flow had water being withdrawn along each reach through diversions on the day the study was performed, as well as significant lengths of heavily vegetated bank sides. Seepage of irrigation water occurs along the entire reach of the West Lateral, probably occurring at higher rates and volumes along the "ridge -top" reach where the ditch was excavated through the shallow soils into the highly fractured sandstone. The two reaches where the ditch featured gains in flow are portions of the general "ridge -top" 11