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<br />. <br /> <br />. <br /> <br />.::> <br />::> <br />~ <br />~ <br />o <br />00 <br /> <br />PROPOSED ANALOG MODEL OF THE ARKANSAS VALLEY <br />IN COLORADO <br /> <br />The irrigation system in the Arkansas Valley originally was developed around <br />surface-water supplies and storage, However, the amount of surface water <br />available varies appreciably in amount with climatic changes The supply is <br />not adequate throughout the irrigation season to all irrigated lands. Consequently, <br />wells have been developed to provide supplemental water to crops during periods <br />of deficient surface-water supplies, Most wells have been drilled since World <br />War II and the number has more than doubled in the past 10 years Irrigation <br />wells were drilled and used, however, with little evaluation of their effect on <br />the surface-water supply, Unplanned development of the ground-water reser- <br />voir has caused a decrease in streamflow and works a hardship on those having <br />surface-water rights downstream from tr.e wells, To minimize adverse effects <br />and to achieve maximum use of the available water supply, ground water and <br />surface water must be developed and managed as a single supply, but develop- <br />ment and management cannot be planned properly until the operation of the <br />hydrologic system is described quantitatively, <br /> <br />The U, S. Geological Survey in cooperation with the Colorado Water Conservation <br />Board and the Southeastern Colorado Water Conservancy District is studying <br />the Arkansas Valley in order to evaluate the hydrologic system so that the effects <br />of selected changes in water management can be predicted. Because of the <br />large area, complex hydrologic interrelations, and bulk of data, quantitative <br />evaluation of the hydrologic system would be extremely difficult without the use <br />of an analog model The model is a 'tool for integrating and analyzing the <br />hydrologic data Ground-water, surface-water, and climatologic data will be <br />simulated by the model to provide a comprehensive description of the hydrologic <br />system and to duplicate present water-management effects on the system. When <br />the model becomes a true analog of the system, then it can be used to predict, <br />quantitatively, the effects of proposed changes in water management. The <br />model will provide a basis for deciding what pattern of pumping and rate of <br />ground-water and surface-water use will be most efficient, <br /> <br />The 174 mile reach of the Arkansas Valley from Canon City to the State line <br />will be modeled, The width of the area studied ranges from 1 to 10 miles, de- <br />pending on the areal extent of the valley-fill aquifer, The basic framework of <br />the model is the ground-water reservoir (physical character and boundaries), <br />Superimposed on this framework are the irrigation canals, the river, and re- <br />charge to and discharge from the ground-water reservoir, Adequate represent- <br />ation of the ground-water system, the irrigation canals, and the Arkansas River <br />will require a scale of 4 inches per m:Je, <br /> <br />After the model is constructed, water-table contour maps at different points <br />in the time will be used to determine if the performance of the model approaches <br />- 3- <br />