5.2 ARKANSAS RIVER BASIN
The primary alluvial aquifer along the Arkansas River consists of unconsolidated river-deposited sediments. The sediments are more varied in size in the upper basin, upstream of Pueblo, ranging from glacial silts to large boulders. In many areas along the upper Arkansas the alluvium is missing where the river is actively eroding in deep bedrock canyons. Alluvium in the lower Arkansas valley is composed of a heterogeneous mix of interbedded sands, gravels, silts, and clays. Alluvium is not a significant aquifer along many of the Arkansas tributaries.
Well depths along the upper Arkansas River range from less than 10 feet to greater than 100 feet below ground surface, with a mean depth of 53 feet. The Division of Water Resources well permit database contains over 3,400 wells that have been completed in the lower Arkansas River valley alluvium. Over 90 percent of these wells are completed at depths less than 120 feet below ground surface with a mean depth of only 58 feet.
Recharge to the Arkansas River alluvium is primarily through infiltration of surface water through the streambed of the river. Infiltration from irrigation canals and surface application of irrigation water also provides a significant amount of recharge to the alluvium downstream from the Pueblo/Crowley County line.