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<br />C 16 9 <br /> <br />The aquifer system in the Albuquerque Basin is composed of Santa Fe Group (middle <br />Tertiary to Quaternary age) and post-Santa Fe Group (Quaternary age) valley and basin-fill <br />deposits. The Santa Fe Group aquifer system is hydraulically connected to the Rio Grande and <br />to a system of canals and drains through the alluvium in the Rio Grande inner valley (fig. 2). <br /> <br />Ground-water withdrawal in the Albuquerque Basin has increased dramatically since the <br />early part of this century. The City of Albuquerque is the largest user of ground water in the <br />basin. Annual ground-water withdrawal by the City increased from about 2,000 acre-feet in 1933 <br />(Bjorklund and Maxwell, 1961, p. 30), to about 59,000 acre-feet in 1970, and to about 123,000 acre- <br />feet in 1994 (files of the City of Albuquerque). More than half of the water the City of <br />Albuquerque has withdrawn from the aquifer since 1932 (a 62-year period) has been removed in <br />the last 15 years--1980-94 (Kernodle and others, 1995, figs. 39-41). Total ground-water <br />withdrawal in the basin was estimated to be about 97,000 acre-feet in 1970 (Thorn and others, <br />1993, p. 54) and about 171,000 acre-feet for the year ending in March 1994 (Kernodle and others, <br />1995, table 6). Of that estimated 171,000 acre-feet withdrawn, an estimated 157,000 acre-feet (92 <br />percent) was withdrawn in the Albuquerque area, 123,000 acre-feet (72 percent) of that <br />withdrawn by the City of Albuquerque. <br /> <br />Management of ground water in the Albuquerque Basin is related to the surface water in <br />the Rio Grande. Because the aquifer system is hydraulically connected to the Rio Grande and <br />water in the river is fully appropriated, any reduction inflow of the river caused by ground- <br />water withdrawal must be offset by owning water rights on the river or by returning water to the <br />river. Under current (1995) regulations, the reduction in flow ofthe river is calculated using the <br />analytical method described by Glover and Balmer (1954). To apply this method, the following <br />assumptions are made: the river is in full hydraulic connection with the aquifer and extends to <br />the same depth as the pumping well, the aquifer is homogeneous and isotropic, and the <br />drawdown in the aquifer is insignificant compared to the thickness of the strata from which <br />water is extracted. However, these simplifying assumptions are not representative of conditions <br />in the river/aquifer system and typically result in an overestimation of the reduction of flow in <br />the river (Sophocleous and others, 1995), Therefore, the flow of the river is augmented by <br />compensating for the flow-volume reduction calculated using the Glover and Balmer (1954) <br />method. This insures that the river flow is protected from the effects of ground-water <br />withdrawaL However, with increasing demands on ground-water resources of the Albuquerque <br />area and decreasing water-levels (Thorn and others, 1993, figs. 28, 30), it also serves to dedicate <br />water to the river that could otherwise be used to reduce stress on the aquifer system. The ability <br />to reliably estimate the effects of ground-water withdrawals on flow in the Rio Grande is <br />therefore, important to the overall management of water resources in the Albuquerque area. <br /> <br />Purpose and Scope <br /> <br />The purpose of this report is to (1) describe the components of the Rio Grande/Santa Fe <br />Group aquifer system, data availability, and data and interpretation needed relating to those <br />components; and (2) present a plan of study to improve understanding of and quantify <br />hydrologic relations between the Rio Grande and the Santa Fe Group aquifer system. Through <br />this quantification, the effects of ground-water withdrawals in the Albuquerque area on flow in <br />the Rio Grande can be estimated using the most up-to-date concept of the river/aquifer system. <br />Because about 92 percent of the ground water withdrawn in the Albuquerque Basin is pumped <br />from wells in the Albuquerque area, the Albuquerque area is the focus of this report. However, <br />the procedures and studies outlined in this report have transfer value to other areas of the basin. <br /> <br />Although the hydraulic connection between the Rio Grande surface-water system and the <br />Santa Fe Group aquifer system is in the inner Rio Grande valley, the interaction of water between <br />the two systems is influenced by movement of water in the aquifer system beyond the inner <br /> <br />3 <br />