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Section 7 Availability of Existing Water Supplies 7.3.1.2 Arkansas Basin Alluvial Aquifer The alluvial aquifer that is associated with the Arkansas River is limited to the area near the river and its tributaries. Alluvium in the upper Arkansas Basin is typically discontinuous due to areas where the river has cut down to bedrock. This is seen in areas like the Royal Gorge and Brown's Canyon (CGS 2003). Once the river passes Pueblo Reservoir, the alluvial aquifer exhibits more continuity and continues uninterrupted to the Colorado-Kansas state line. The alluvial aquifer has a maximum thickness of 250 feet on the valley floor. The alluvium in the tributary streams ranges from 0 to 50 feet (Byler et al. 1999). Like the South Platte River alluvial aquifer, this aquifer has a high hydraulic conductivity in its lower reach downstream of Pueblo Reservoir and is very productive. It is replenished by return flows from irrigation of adjacent lands and is ~~ considered a renewable resource. However, the groundwater in this aquifer is considered tributary to the Arkansas River and users of this resource are administered under the Prior Appropriation System. Except for domestic or other low-volume exempt uses, the use of groundwater in this aquifer requires a water court-approved augmentation plan that describes how depletions to the river will be offset to avoid injury to senior appropriators and to comply with the interstate compact with Kansas. Rulemaking by the State Engineer in 1996 requires all wells to have meters installed so that total amounts withdrawn can be better regulated. This may have the effect of reducing future withdrawals to comply with the interstate compact. The location and extent of alluvial aquifer in the Arkansas Basin is shown in Figure 3-6. ~~ Statew~itle Water Supply Inii'iative 7-14 S:\REPORT\WORD PROCESSING\REPORT\S7 11-10.04.DOC