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The shallower Alluvial Aquifer no longer contains the quantity of groundwater needed to irrigate all of the region's rice fields and water other agricultural crops. This aquifer is expected to be depleted for commercial use by the year 2015 and drilling wells deeper into the region's Sparta Aquifer accelerates depletion of the region's more valuable supply of drinking water.
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A young white-tailed deer sprints through flooded lowlands in the Grand Prairie area of eastern Arkansas.
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If the growing demand for groundwater can not be supplemented with an alternative source, the area's natural streams will continue to be pumped dry during the growing season and the aquifers' ability to retain surface water for recharge could be lost.
The Alluvial Aquifer lost its ability to fully recharge around 1915, when farmers began digging wells into this groundwater source for most of the region's annual rice and other agricultural crop irrigation needs. Once reachable at just 50 feet below the Grand Prairie's surface, this aquifer has now receded into what geologists say is a "cone of depression" reaching depths of more than 120 feet in some locations.
Recharge of the Alluvial Aquifer is dependent upon the White River to the east and the Arkansas River to the west. Together these two rivers account for about two-thirds of the aquifer's annual recharge capability. However, the prolonged lack of rainfall throughout the White River basin further limits this aquifer's capacity and its recharge ability.
While many of the Grand Prairie's commercial users are switching to the deeper Sparta Aquifer, most public works officials say this is not a long-term solution to the drying of the Alluvial Aquifer, because the area's municipal water systems rely on the Sparta Aquifer to provide drinking water. According to Arkansas Groundwater Law, they are correct because water use for drinking water holds priority rights over agriculture needs. The Alluvial and Sparta Aquifers below the Grand Prairie region meet the legal definition of "critical groundwater areas," as defined by state law.
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The saturated thickness of the shallow Alluvial Aquifer is projected to continue shrinking at a rate of approximately one foot each year, with less than 20 feet of water-bearing sand existing under most of the Grand Prairie by 2015.
Source: U.S. Geological Survey (USGS)
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