1988-04-11_PERMIT FILE - C1981008A (23)

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return flow occurring in the area) with a narrowly incised channel up to four feet in depth. There are limited primary terrace areas directly adjacent to the channel. Valley bottom widths are from less than 100 feet to about 500 feet consisting of poorly reworked unconsolidated streamlaid deposits with isolated pockets of weathered colluvium. In the reconnaissance investigation study, about 20 acres along Tuttle Draw were found to be underlain by unconsolidated streamlaid deposits. These areas are not considered extensive enough for effective irrigation. The proposed Nucla East mining is located entirely within the Calamity Draw watershed (7.0 square miles) which is less than half the size of the Tuttle Draw watershed. Calamity Draw is also an upland drainage area that is tributary to the San Miguel River. The middle and upper portion of this watershed (the First Park) has been intensively irrigated and cultivated since about 1910. Presently, the watershed is comprised of irrigated pasture, rangeland, and the town site of Nucla. Agricultural and irrigation practices have resulted in a disjointed tributary drainage pattern which is almost completely controlled by the return ditches of the irrigation network. Most of the tributaries, especially in the mid and upper portion of Calamity Draw, are intermittent with flow being controlled by the timing and application of irrigation water. Calamity Draw, in the vicinity of`the Nucla East mining area, is a perennial, meandering stream with a narrow incised (up to three feet) channel. The banks are stable as a result of vegetation encroachment. Calamity Draw has the same valley bottom widths and geomorphic features as Tuttle Draw, but is less steep and confining. The perennial flows of both draws are due to irrigation return water and the limited baseflow is maintained by overburden ground water discharge. The overburden aquifer is recharged from the upland irrigation system. Irrigation. The area in the vicinity of Nucla and Nucla East has (since about 1910) had an extensive man-made irrigation system. The water used for flood irrigation is diverted from the San Miguel River approximately 15 miles east of the Nucla Mine by the Colorado Cooperative Ditch Company. The irrigation ditches transect basins and commonly run along the basin divides (see Exhibit 7-1 for the exact location of the irrigation ditches). The main irrigation ditches have a network of feeder ditches running from them for irrigating outlying fields. These ditches are a source of ground water recharge, causing ground water mounding in the shallow ground water aquifer system. The effects of mounding near the Nucla Mine are apparent from monitor well water levels and hydrographs (see Appendix 7-2). Perennial flow occurs in Tuttle Draw as a result of ground water discharge and 16-12 Revised 04/11/88