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'~ \ I " I ,. i i ; \' , I Water and Storage Needs Assessment SECWCDI Assessment Enterprise December 10,1998 . Providing at least 700 cfs (at the Wellsville Gage) during the July 1 - August 15 period primarily to support rafting. . Limiting daily changes in flows to 10 - 15 percent. The District has concurred with the flow management plan outlined above but has indicated that releases from Project storage should be limited to 10,000 af, unless the District approves more and releases should be subject to water availability and storage space limitations. 2.1.4 Ground Water Ground water in the Arkansas Basin occurs in the valley fill alluvial aquifer, alluvial aquifers along tributaries to the river, the High Plains aquifer, and bedrock aquifers. The valley fill and High Plains aquifers have characteristics that support significant development for large M&I and irrigation supplies. The High Plains aquifer is administered under the Colorado Ground Water Management Act of 1965, based on a modified doctrine of prior appropriation. Alluvial ground water is generally considered to be tributary to surface streams and is administered as such. Prior to 1996, ground water in the Dakota and Cheyenne Formations east of Canon City was not administered as part of the surface systems. Stream depletions caused by new wells require replacement pursuant to an administratively approved substitute water supply plan or a judicially approved augmentation plan. Ground water in the Denver Basin aquifers in the area of Colorado Springs is governed by rules and regulations and a permit system promulgated in 1985. As described later in Section 2, various water supply entities rely extensively on non-tributary .and tributary wells for their water supplies. The majority of ground water use in the Basin is, however, for irrigation. Development of the valley fill aquifer primarily for irrigation supplies increased steadily from 1940 to 1965 between Pueblo and John Martin Reservoir. Since 1965, the number of wells has held fairly constant. Mean annual pumping of the valley fill aquifer was estimated to average 100,000 af/yr between 1974 and 1985 from wells located between Pueblo and John Martin Reservoir, based on studies reported on by Boyle Engineering (1988). In 1995, the Colorado State Engineer amended the rules governing the diversion and use of tributary ground water in the Arkansas Basin. The amended rules were upheld by court decree in 1996. Under these regulations, well owners must furnish water to replace depletions with respect to senior ditches in Colorado and to usable flow at the Colorado-Kansas state line, pursuant to a decreed augmentation of substitute supply plan. These rules apply to the valley fill aquifer of the Arkansas River between Pueblo and the state line and the alluvium of Fountain Creek. As part of the rules and regulations, well owners have been required to submit monthly pumping or power use records. 97411\Final_l\TEXT_AWPD m GEl Consultants, Inc. 2-5