USGS scientists reported the findings of a three-year study on Moab and Castle Valley groundwater in a public meeting on September 21. The results indicate that the safe yield for the area is likely between 12,000 and 14,000 acre-feet of water per year, rather than the 13,000 to 17,000 ranges previously estimated.
The study was initiated by the state of Utah in response to water rights applications in the Spanish Valley area. It is the first comprehensive evaluation of the Moab-Spanish Valley groundwater budget since the 1970s, said USGS hydrologist Melissa Masbruch, a member of the study team.
The study aimed to understand the water budget, a term for the annual recharge and discharge to the aquifer system.
“The groundwater budget is a more practical measure of groundwater availability ... than the total storage of the system,” USGS Scientist Victor Heilweil told The Times-Independent. “Total storage is generally not considered for sustainable development since groundwater withdrawals exceeding the total recharge or discharge ... from the system could cause widespread declines in groundwater levels.”
The USGS team focused on calculating water discharge, Masbruch said, which is related to recharge.
“No long-term declining trends in groundwater are currently being observed. This suggests that the groundwater system appears to be in equilibrium, and that recharge is approximately equal to discharge as far as we can tell,” Masbruch said.
Where does Moab’s water come from?
Moab relies on two aquifers for water: the valley-fill aquifer under Spanish Valley and the Glen Canyon Group aquifer northeast of town. It was previously thought that the Glen Canyon Group aquifer was the primary source of recharge for the valley but the recent study found signs that indicate that might not be the case.
“Pack Creek, rather than Glen Canyon Group Aquifer, is the primary source of recharge to the valley aquifer and most of the recharge to the Glen Canyon Group Aquifer is occurring at high elevation in the La Sal Mountains,” said USGS hydrologist Nora Nelson during the public meeting.
That means that Moab’s water is coming from the La Sal Mountains rather than being collected from the Navajo sandstone between Moab and Castle Valley.
The scientists proposed several next steps for Moab to take, including gauges, monitoring one of the large springs near the golf course and developing a groundwater model.
Arne Hultquist, director of the Moab Area Water Partnership, said that the study results mean that water conservation might be needed sooner than previously expected.
“[Conservation] was necessary prior to the study because current allocated water rights will not meet the demand of impending development. However, the City, [Grand Water and Sewer Service Agency], and [Spanish Valley Water and Sewer Improvement District] should realize that water conservation will be needed to meet the demand for water sooner than what might have been expected because the estimated sustainable aquifer development is less than previous estimates.”
Hultquist said that adding new water gauges to Pack Creek and Mill Creek would be necessary to develop an accurate groundwater model, which would be useful to “fine tune” the groundwater management plan.
“I would encourage local institutions to work together to fund the gauges for this purpose,” Hultquist said. “If these steps are not taken now I am sure they will be sometime in the near future because as available water becomes scarce its value will increase. The value of water in our area will eventually drive the acquisition of data and development of tools that can be used to maximize the use of the limited resource.”
A new groundwater
management plan for Moab
The Utah Division of Water Rights (DWR) will use the results of the study to develop a groundwater management plan for the area. Marc Stilson, southeastern regional engineer for DWR said that the goal of the plan would be to protect the aquifer.
“The objectives of the proposed groundwater management plan are to limit groundwater withdrawals to safe yield, protect the physical and chemical integrity of the groundwater aquifer and protect water quality,” Stilson said.
There are currently more than 20,000 acre-feet of water rights allocated on paper. Municipal usage, irrigation from groundwater and domestic wells add up to 3,900 acre-feet per year of water used currently, according to Stilson.
“Most of [the water rights are] held by Moab City, Grand Water and Sewer Service Agency and San Juan Spanish Valley Special Service District and is not currently in use … the remaining water rights are either being held for the future projected use of these municipalities or have been abandoned by small domestic users,” said Stilson.
The USGS report still needs to go through a review process before results can be determined to be final. Once the final report comes out, which USGS scientists said should happen within a year, the DWR will study the document, hold public meetings to receive water user and stakeholder input, develop policy recommendations and submit those recommendations to the state engineer, who will establish the groundwater management plan, said Stilson.
“The real value of the USGS report and development of a groundwater management plan is to put the focus on protecting this valuable resource and encourage the major municipal water right holders to invest in long term planning and management of their water rights,” Stilson said.