The Arkansas River in southeastern Colorado and westernmost Kansas is one of the most saline rivers in the U.S. The salinity of river water entering Kansas derives from substantial concentration of dissolved solids by consumptive losses in Colorado. Water levels have declined in the High Plains aquifer in southwest Kansas from consumptive use of ground water and decreased recharge from smaller river flows. Starting in the 1970s, the Arkansas River ceased continuous flow during most years along as much as 150 miles in southwest Kansas. The saline river water enters the subsurface along the river bed; water is also diverted and used conjunctively with fresh ground water for irrigation.
Heavy snow melt from the Rocky Mountains and rainfall in eastern Colorado filled reservoirs of the Arkansas River basin in Colorado in the summer of 1995. Colorado released large amounts of water to Kansas during July, causing the first complete throughflow in the river since 1988. Nearly 90% of the July 1995 flow into Kansas remained in southwest Kansas; most of the water seeped into the aquifer underlying the river. The river again ceased flowing completely through the state by the latter part of August.
The river water is sodium-sulfate chemical type; sulfate concentrations can reach 2,400 mg/L during low flows. The lowest sulfate observed during the high flow of July 1995 was about 700 mg/L. Based on current conditions, in about 40 years river water seepage has the potential to contaminate all of the High Plains aquifer underlying a 500 square mile corridor of the valley to a sulfate concentration over 400 mg/L (the maximum level proposed by the U.S. for drinking waters). However, lower permeability clay, silt, and caliche layers restrict the subsurface movement of the contaminated water. The ground waters which could become contaminated are the sole sources for several towns and cities. Management and protection of fresh ground waters will be critical to maintain water quality for municipal and special agricultural and industrial uses.
Kansas Geological Survey
Updated April 17, 1997
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