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<br />Water Supply and Use <br /> <br />The water supply for the Gunnison River comes principally from the melting <br />of winter snawpacks on the high mountain peaks, augmented by summer precipi- <br />tation. There is considerable variation in watershed yield, reflecting <br />climatological and meterological differences in the different parts of the <br />Basin. Water yields range from 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 of the Basin. Even within the higher parts of the <br />Basin, significant differences occur in the watershed yield. <br /> <br />The dominant use of water within the Basin 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 />streamflows 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 Bas in. <br /> <br />The rate of streamflow diminishes during the late summer and in many instances <br />becomes insufficient to meet the crop requirements for irrigation water. <br />Shortages of late-season water are common on tributary streams in those areas <br />which depend on direct diversion of 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 number of small <br />reservoirs located on Grand Mesa and elsewhere, which furnish at least a <br />partial supply during the latter part of the irrigation season when the <br />natural streamflows are inadequate to meet the irrigation demands. <br /> <br />Additional stream 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 projects <br />would contribute materially to the stabilization of the irrigated agriculture <br />within the Basin. 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 project 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 from salt or sediment producing areas characteristically <br />contain undesirable amounts of sediment or dissolved salts. 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 />occurrence, and they have little influence on the quality of the water supply <br />of the Basin as a whole. <br /> <br />- 12 - <br />