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I I I I I I I I I I I I I I I I I I I Section 4 - E\i,\ting C%mi!o \Vater SlIpp/ie.\ "The total water supply available to the state is derived through a complex usage of supplies from several sources. Supplies pumped from deep and shallow aquifers usually have close relationship with the surface water supply"" "The annual surface runoff in any particular stream var- ies widely from year to year depending on the precipita- tion. Other factors that influence the runoff are the soils, topography, geology, and vegetative cover. The average annual runoff ranges from 20 inches in the high moun- tains to less than 0.25 inches in the arid parts of the pla- teau and plains sectors of the state"" "Approximately two-thirds of the runoff occurs over one- quarter of the year. The seasonal timing of runoff has resulted in the development of many surface reservoirs to capture the spring runofffor use later in the year". Water supplies usedfin' irrigation result in greater depletions than any other purpose. However, substantial return flows are put to successive uses. "Water depletions in the state occur as a result of the uti- lization of a complex surface and ground water resource system. Some uses such as the generation of hydroelec- tric power cause little, if any, depletions. Also, in most cases water depletions for fish and wildlife, and recre- ational uses are minor; however, there can be substantial non-beneficial evaporation losses from reservoirs kept full for these uses. Water supplies used for irrigation result in much greater depletions than any other purpose or com- bination of purposes. However, substantial return flows result from irrigation which are in turn put to successive uses. Other uses which result in lesser but substantial water depletion are municipal and industrial use, and min- ing and processing of minerals. "As of 1993, more than 10 million acre-feet of waterleave the state in an average year. Of that amount, approxi- mately 87% flows west from the Continental Divide to- ward the Pacific Ocean and 13% flows east toward the Atlantic Ocean. The location of the state's water supply is in direct contrast to the location of consumptive use in the state, with approximately 25% located west of the Continental Divide and 75% located east. The difference in location between water supply and demand has resulted in the development of 24 trans mountain diversions within the state". 4-2 ~. COLoraDo ,_. Farm Bureau