High Plains States Groundwater Demonstration ProgramParts1&2

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Groundwater and Recharge Groundwater resources are intensively tapped in the Western United States. Although the total potential volume of water in aquifer formations is vast, the inherent characteristics of groundwater, recharge processes, hydrogeologic conditions, and recharge technology can pose practical limitations on artificial (induced) recharge and recovery efforts. The National Academy of Sciences provides a concise perspective of issues facing water resource use and the importance of groundwater reserves. Ground water is a far more important resource than is often realized — excluding the water locked in glaciers and icecaps, about 97 percent of the world's fresh water is ground water, while streams, rivers and lakes hold only about 3 percent (Bouwer, 1978). In the United States, about one -half of the population and three - fourths of the public water supply systems rely on ground water. Ground water also provides a critical source of water for agricultural irrigation and industries. But as is often the case with critical resources, ground water is not always available when and where needed, especially in water -short areas where heavy use has depleted underground reserves (NAS, 1994). A report of the Western Water Policy Review Advisory Commission (WWPRAC) offers a brief discussion of groundwater overdraft in reference to sustainable water use. Even though it is widely understood that ground- and surface -water resources are interrelated, most states continue to manage ground and surface water by different legal regimes... The net result is that state laws commonly allow groundwater overdraft —the depletion of an aquifer at a rate faster than the natural rate of recharge (WWPRAC, 1998). Selected paragraphs from Leopold's basic primer on water further illustrate fundamental issues concerning groundwater use and recharge in the and West. In some areas of the United States, rainfall is so scanty that only occasionally does enough fall to add any appreciable amount to the ground -water table. In some and parts of the western United States water is being pumped that fell as rain during the ice age, at least 10,000 years ago... It should be kept in mind that water moves so slowly underground that replenishment by rainfall may take months or years... If the amount of water in storage is large, the water level may decrease slowly and a long time may be required to determine whether the aquifer is being overpumped (Leopold, 1974). These excerpts point to the need for proactive planning, both for effective implementation of local or seasonal recharge efforts and to avoid crisis water shortage conditions caused by inadvertent or unrecognized groundwater depletion. The linkage between surface and groundwater is unavoidable (Winter et al., 1998). Progressive drawdown of groundwater can reduce water flow into dependent streams. Conversely, surface water supplies must be sufficient to satisfy water uses, instream flows, and allow for recharge. Moreover, in many situations, the quality of groundwater and surface water are inextricably linked. Program Summary Report Part I — Overview, Results, and Findings 1•y