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<br />Artificial Recharge of Ground Water in Colorado <br />A Statewide Assessment <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Backt!round <br /> <br />Colorado is a semi-arid state with a rapidly growing population that is straining a limited water- <br />resource base. Compounding the situation is the geographic imbalance of water supply with <br />water demand. The greatest amount of precipitation, and hence the greatest runoff of surface <br />water, occurs on the Western Slope of Colorado's Rocky Mountains, yet the greatest number of <br />people live on the Eastern Slope ofthe Rockies. A second imbalance exists in the relative timing <br />of supply and demand. The greatest supply falls in the late winter and spring, while the greatest <br />demand occurs in the summer well after the supply has peaked. These factors mandate careful <br />management of the limited resource to provide a sustainable supply. In Colorado, management <br />ofthe water resource has evolved into a complex system of water law, which attempts to allocate <br />the limited resource fairly, and a complex infrastructure system to distribute the limited resource. <br />The infrastructure system includes numerous water storage facilities and a series of trans-basin <br />diversions that generally move water from west to east, across and under, the Continental Divide. <br /> <br />Sustainable water management relies on the ability to store water. The traditional method of <br />storing water has been to construct dams and develop reservoirs (Fig 1-1). However, the high <br />cost and long timeframes combined with adverse ecological, environmental, and socio-cultural <br />impacts have hindered construction of new large reservoir projects in the west. In addition, <br />surface reservoirs lose tremendous amounts of water to evaporation (especially in the semi-arid <br />west); require expensive maintenance due to sediment accumulation; have the potential of <br />structural failure; are vulnerable to contamination, whether accidental or by criminal acts; <br />increase breeding areas for disease carrying insects; and interfere with river ecology. A viable <br />alternative is the storage of water below ground in aquifers, which are natural reservoirs. <br /> <br />Ground water has long been an important water resource in parts of Colorado, particularly on the <br />Eastern Slope where surface-water supplies are limited. In fact, many regions and communities <br />are completely dependant on ground water for agricultural and municipal supplies. Much of the <br />rapidly growing southern Denver Metropolitan region is currently dependant on non-renewable <br />ground water extracted from the Denver Basin aquifer system. As a result ofthe extensive <br />development of ground water to meet a rapidly growing population, ground-water supplies are <br />being depleted and water levels are declining. For example, water levels in the Denver Basin <br />Arapahoe aquifer southeast of Denver are dropping at rates up to 30 feet per year (ft/yr) (DWR, <br />2000). <br /> <br />In addition to water supply, aquifer storage can be utilized as part of an overall water <br />management strategy. This storage potential can be used in the short-term, season-to-season <br />balancing act between natural supply and demand, or to provide a cushion for periods of drought. <br />Referred to as conjunctive use, surface water is used as the primary source of water in periods of <br />abundance, while ground water is reserved for times when surface water is limited. When <br />necessary, natural ground-water recharge can be enhanced to take advantage of peak surface- <br />water flows. Aquifers represent tremendous opportunities for underground storage of water with <br />essentially zero evaporative losses. <br /> <br />3 <br />