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<br />· Obtain review from Division Offices of the Division of Water Resources. <br /> <br />· Obtain Colorado Water Conservation Board and other interested party review. <br /> <br />· Incolporate comments received. <br /> <br />· Prepare a fmal report. <br /> <br />1.3 Background <br /> <br />As an overview, the following discussion of Colorado's water supply is taken from the report <br />"Water for Tomorrow, Colorado State Water Plan", (USBR, CWCB, February, 1974): <br /> <br />The total water supply available to the state is derived through complex usage of supplies from <br />several sources. Supplies pumped from deep and shallow aquifers usually have a close <br />relationship with the suiface water supply. The normal water supply situation including state <br />water outflow and Transmountain diversions that prevailed in 1970 is summarized in Table 1.1. <br />(In order to update Table 1.1 from 1974, it required many assumptions to be made. Updated <br />infonnation was supplied where readily available, however, it highlights the need for updated <br />data to complete an accurate water budget for the state. The most difficult part of Table 1.1 to <br />detennine is the water depletions portion that requires significant data on diversions, <br />consumptive use and return flows. This component of the water budget is discussed in Section <br />3.0). <br /> <br />The annual suiface runoff in any panicular stream varies widely from year to year depending <br />upon the precipitation. Other factors that influence the runoff are the soils, topography, <br />geology, and vegetative cover. The average annual runoff ranges from 20 inches in the high <br />mountains to less than 0.25 inches in the arid parts of the plateau and plains sectors of the state. <br />By sub basins, the Upper Colorado sub basin experiences the highest runoff, the average annual <br />being 6.6 inches. The Republican River sub basin has an average annual runoff of 0.4 inches <br />which is the lowest in the state. <br /> <br />The water depletions in the state occur as a result of the utilization of a complex suiface and <br />ground water resource system. Some uses such as the generation of hydroelectric power cause <br />little, if any, depletions. Also, in most cases water depletions for fish and wildlife, and <br />recreational uses are minor,' however, there can be substantial non beneficial evaporation losses <br />from reservoirs kept full for these uses. Water supplies used for irrigation result in much greater <br />depletions than any other purpose or combination of purposes. However, substantial return <br />flows result from irrigation which are in turn put to successive uses. Other uses which result <br />in lesser but substantial water depletion are municipal and industrial use, and mining and <br />processing of minerals. <br /> <br />Interstate compacts require Colorado to pennit specified quantities of water to cross its <br />boundaries into other states for downstream use. In addition to the outflows required to satisfy <br /> <br />6 <br />