2012-01-06_PERMIT FILE - C1982057A (4)

Home Browse Search

• Before the advent of farming practices in these dryland areas, a delicate balance existed between the native vegetation and the average annual precipitation. Following the initiation of farming in these arid areas, it was recognized that there was a strong probability that there would be insufficient moisture to support annual cropping. Thus, summer fallowing is conducted on 50 percent of an operator's cropland acreage in any given year with the intent of maximizing soil water content for the highest possible crop yields. While fields are in fallow, recharge from snowmelt and rainfall in excess of the soil's water holding capacity flows downward under the influence of gravity, dissolving salts as it moves along. This is the principal mechanism for the creation of saline seeps. In wetter years, soil water may be in excess of crop requirements, further compounding the situation. Because the crops are not as efficient at using water as the native plants li.e., annual crops extract moisture from much shallower depths of the soil profile than perennial speciesl, cropped lands will also contribute to excess soil water build-up and downward unsaturated flow. These sources of unsaturated flow below cropped lands, though not of the magnitude of flow beneath (allowed areas, also contribute to the formation of saline seeps. Evidence of these salt deposits and saline seeps in dryland farming areas in the lower Dry Creek drainage can be seen in numerous aerial photographs of the area. Though the duration of the high TDS spoil flow into Dry Creek streamflow will be long-term and the • magnitude of the increases compared to background levels is high, no downstream water uses will be injured. The two farmed fields above J.C. Temple Reservoir #2 (see Exhibit 16-3, Section 91 are subirrigated and may be impacted by salinity increases in Dry Creek. However, these two small fields contribute to less than three percent of the owner's total income (personal communication with Jean Olson, March 1, 2004), and therefore, by CDMG guidelines, are insignificant. The fields below J.C. Temple Reservoir #1 are flood irrigated by water from J.C. Temple Reservoir #1, Emrich Reservoir, and Greasewood Flat Reservoir, not water from Dry Creek. Beyond this point, the irrigation return flows and dryland farming saline seeps degrade the Dry Creek chemistry to such a degree that separate effects from spoil discharges are unmeasurable and greatly exceeded in magnitude. Based on the above information, the spoil discharge impacts to the Dry Creek water quality have little significance. The magnitude of the TDS and chemical load increase in Sage Creek as a result of spoil discharge to Sage Creek is small (two percentl. The extent of the impact would probably be limited to within one mile downstream of the confluence of 009 tributary and Sage Creek as any additional dilution effects would render the changes unmeasurable. The small magnitude of TDS increase would have a long duration, but negligible significance 7R-50 53 Revised 11/04