Investigation of the extent of fresh and brackish groundwater to inform better management of decreasing groundwater levels in the Willcox Basin, SE Arizona

Tiffani Cañez, Jennifer McIntosh, and Grant Ferguson1

Hydrology and Atmospheric Sciences
The University of Arizona

Adoption of the recent Lower-Colorado River Basin Drought Contingency Plan will make Arizona more dependent on groundwater to meet water resource demands. Knowing the extent and distribution of fresh and brackish groundwater in relation to existing wells and water table elevations would enable water managers and users better quantify how much water is feasibly available. This study focuses on the Willcox Basin in southeastern Arizona, where groundwater levels have experienced significant declines, yet there is continued high demand for groundwater for irrigated agriculture. In the early 1980s groundwater withdrawals decreased, however, in 2000 withdrawals began to increase again and have continued to increase since. The current water table is approaching depths of existing water wells in some locations. North of the Willcox Playa depth-to-water is about 400 ft at the deepest, about 350 ft south of the playa, and around the Willcox Playa closer to 150 ft. Freshwater extends to an average depth greater than 280 ft, except near the playa where brackish water extends to approximately 40 ft. It is still unknown how much deeper freshwater extends or if water becomes brackish with depth due to the lack of deep wells in the basin or geophysical surveys.

1Department of Civil, Geological, and Environmental Engineering, University of Saskatchewan, Saskatoon, Canada

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