Converting from Surface to Sub-Surface Water Storage: An Indirect Experiment in Kansas

In many parts of the U.S. surface flow is projected to decline because of global warming. This change will greatly increase the importance of groundwater-surface water interactions, and may force conversion from surface to subsurface storage of water resources in many cases. Delivery of surface-stored water via a stream to groundwater extraction wells near Russell, KS is an ongoing indirect experiment in just such conversion.

During the 2006 water year two intentional releases were made from Cedar Bluff Reservoir southwest of Hays, KS to transfer a total of 2000 ac-ft of water 36 river miles downstream for extraction at the Pfeiffer Wellfield. Previous geophysical characterization of the intervening alluvial aquifer at Hays' Smoky Hill River Wellfield(SHRW) allows estimation of the total increase in groundwater storage resulting from these releases. A total of 3988 ac-ft were released in December and August. SHRW, 24 river miles downstream from Cedar Bluff experienced a subsurface storage increase of 900 ac-ft, while the Pfeiffer wellfield recovered the expected 2000 ac-ft. 40-50% of the releases were lost to the intervening alluvial aquifer, but only 27% was "unrecoverable losses" infiltrated outside the wellfields. Releases were discontinued when reservoir levels dropped precipitously.

These losses are small compared to current surface storage losses. Since 1990 70% of inflows to Cedar Bluff Reservoir were lost to evaporation. Predicted future streamflow reduction indicates Cedar Bluff has a 50% chance of falling below gravity-accessible storage by 2050, resulting in 100% loss of inflows. Under these circumstances, permanent conversion from surface to groundwater storage may be the only viable choice to minimize storage losses and efficiently maintain water resources. This will require a difficult choice between preserving consumable water resources or recreational uses, and looms as a daunting challenge for Kansas and many other arid and semi-arid regions of the U.S.