Artifical Recharge of Ground Water in Colorado

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