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August 16, 2019

A new assessment of groundwater resources in the Spanish Valley watershed in southern Utah shows an amount that is about 30–40% lower than previously reported, according to a U.S. Geological Survey report.

Future growth in the Moab, Utah, area is dependent on adequate water resources. With surface waters fully appropriated, water needs to support future development must be met with groundwater resources. The last assessment to determine how much groundwater is available in the Spanish Valley area was completed in the 1970s.

“These findings will be useful to local and state water managers in evaluating how much additional development can be sustained in the Moab area with the groundwater available,” said lead author and USGS scientist Melissa Masbruch. “This information can also help decision-makers make informed choices as they develop a future groundwater management plan.”

The total amount of groundwater entering and leaving the aquifer system within the Spanish Valley watershed is estimated to be 13,000 to 15,000 acre-feet per year. This estimate is based on the amount of groundwater flowing out of the aquifer, which provides a more robust assessment of how much water is in an aquifer system than recharge measurements. This current estimate is about 30–40% lower than the 1971 estimate of 22,000 acre-feet per year.

The Spanish Valley watershed includes the valley-fill and Glen Canyon Group aquifers. Results show that there is no significant groundwater inflow from the Glen Canyon Group aquifer to the valley-fill aquifer. Rather, inflow to the valley-fill aquifer was found to come from the Pack Creek watershed. This is in contrast to findings from the 1971 assessment’s assumption that 14,000 acre-feet per year of groundwater enters the valley-fill aquifer from the Glen Canyon Group aquifer. Findings also show a groundwater outflow of 300 to 1,000 acre-feet per year from the watershed to the Colorado River. This amount is much lower than the 1971 estimate of 11,000 acre-feet per year.

For this study, scientists collected water-quality, water-level and flow data from wells, springs and streams in the Spanish Valley watershed from 2014 to 2016. Water-quality and water-level data were used to determine the sources of groundwater recharge and flow throughout the aquifers. Flow measurements helped to assess groundwater discharge to streams and springs and were used to determine inflow and outflow to the aquifers.

This study was done in cooperation with the Utah Division of Water Rights, City of Moab, Grand and San Juan Counties, Grand Water and Sewer Service Agency, Utah School and Institutional Trust Lands Administration, The Nature Conservancy, Utah Division of Wildlife Resources, Living Rivers, San Juan Spanish Valley Special Service District, U.S. Bureau of Land Management and the U.S. Forest Service.