Big Chino Aquifer Monitoring Program
An agreement between two Yavapai County communities and SRP is ensuring that a critical water supply for the Verde River is protected for generations to come.
The agreement between SRP, city of Prescott and town of Prescott Valley ensures a continued flow from the Big Chino aquifer into the headwaters of the Verde.
This, in turn, helps increase the certainty of the Verde’s ability to support the wide range of recreational, agricultural and municipal uses along its 170-mile course — from its headwaters to its confluence with the Salt River near northeast Mesa.
Comprehensive Agreement #1 is a three part plan to monitor, model and mitigate, as needed, impacts in the Big Chino Sub-basin. The Big Chino is a massive underground aquifer believed to contribute 80–86% of the source water of the headwaters of the Verde River near Paulden.
A portion of Prescott and Prescott Valley’s future water supply may be derived from pumping water from the Big Chino aquifer under an exemption from the Groundwater Transportation Act. The agreement is aimed at ensuring that pumping under the exemption will not have detrimental effects on the historical flow from the outlet of the Big Chino aquifer into the Verde River.
The aquifer releases 14,000 to 18,000 acre-feet of water into the Verde River annually. During the dry summer months, this can account for 10–15% of the Verde’s baseflow as measured above Horseshoe Reservoir.
Under terms of the agreement, ongoing monitoring and data collection will help to develop a robust groundwater flow model to predict future impacts. This model will be also used to identify triggers to determine if mitigation is needed to offset impacts of pumping on the Verde River.
Prior to the arrangement, SRP, Prescott and Prescott Valley appeared headed for litigation. But the 2010 agreement ensured that all parties could address their primary concerns — enhancing available water supplies for the two municipalities while protecting the flow of the Verde River — without costly distractions.
The execution of a long-term monitoring plan in 2012, fully funded by the parties, has resulted in 12 additional stream flow sites; the collection of gravity and geophysical data; an assessment of existing wells for monitoring purposes; several annual crop surveys; and the hiring of a third party (Golder Associates) to develop the groundwater flow model.
As important: The plan has SRP, Prescott and Prescott Valley working on the same page — an important achievement critical to sustaining water supplies for all Arizona communities and users that rely on the Verde River and its complex watershed.