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<br />I' <br />C) <br />~ <br />,..~ <br /> <br />Water Supply and Use <br /> <br />The water suppcly for the GunniSQn River comes principally from the melting <br />af winter snowpacks on the high mountain peaks, augmented by summer precipi- <br />taticm. There is considerable variation in watershed yield, reflecting <br />clima~lQgical and meterological differences in the different parts of the <br />Basin. Water yields range fram more than 30 inches of runoff in parts of <br />the Anthracite Range, West Elk, and San Juan Mountains, to less than 1 inch <br />in the lower, drier parts .f;f the Basin. ~en within the higher parts of the <br />Basin"significant differences occur in the watershed yield. <br /> <br />The dominllnt use of water within the Rasin is for irrigation. The climatic <br />regime is such that . successful crop; production is impossible without supple- <br />menting the natural rainfall by irrigation. Total annual water yield of the <br />Basin exceeds total water-supply requirements within the Basin. Since the <br />streamf!aws are mainly derived from snow melting, they are quite variable. <br />The peak flows characteristically occur in the late spring and early summer. <br />Runoff during this period is generally in excess of immediate requirements <br />throughout the Rasin. <br /> <br />The rate of streamflow diminishes during the late summer and in many instances <br />be_s insufficient. to meet the crop requirements for irrigation water. <br />Shq.rtages of late-season water are cOlll1lWn on tributary streams in those areas <br />which depend on direct diversion ocf natural streamflow for their irrigation <br />supplies. These shortages are frequently quite severe, and limit the agri- <br />cultural development and production in several parts of the Basin. <br /> <br />There is only limited regulation of streamflow at present, with Taylor Park <br />Reservoir on the Taylor River being the most important regulating reservoir <br />within the Basin. Equally important to specific areas are a munber of small <br />reservoirs located on Grand Mesa and elsewhere,. which furnish at least a <br />partial supply during the latter part of the irrigaticm season when the <br />natural streamflows are inadequate to meet the irrigation demands. <br /> <br />Additional str.eam regulation is needed within the Basin to meet seasonal <br />requirements and to smooth out the annual variations of water supply. Projects <br />.presently authorized or proposed and under study will go far towards meeting <br />these needs for the major irrigated areas. Additionally, smaller prajects <br />would contribute materially to the stabilization of the irrigated agriculture <br />within the Basino Potential projects of this type are noted in succeeding <br />.sectionS of the report. there is a need for a. uniform acceptable criteria <br />for determining the suitability of land for irrigation and the selection of <br />new projeet lands. <br /> <br />The water supply of the Basin is of excellent quality. Generally, it is well <br />suited to long continued irrigation of the farmlands. There are, however, a <br />few places in the lower part of the Basin where return flows from irrigated <br />areas or inflows fram salt or sediment producing areas charaCteristically <br />c~ntain undesirable amounts of sediment or dissolved saltso These flows are <br />small in amount and are rapidly diluted by the larger streams into which they <br />flow. Their effect is therefore limited to the immediate location of their <br />o-ecurrence, ana they have little influenee on the quality of the water supply <br />of the Basin as a whole. <br /> <br />- 12- <br />