Recent actions affecting the San Pedro River highlight key differences in state and federal laws for regulating water.
Arizona regulates surface water and groundwater independently, artificially dividing two resources that are naturally linked. Both stakeholders and the courts recognize that this approach is often imperfect, and they have been working for decades to find a better solution. The potential conflicts are particularly apparent in the San Pedro River basin, which is home to Sierra Vista, a growing population center, and Fort Huachuca, an important Army base.
As the last major, free-flowing, perennial river in the Southwest, the San Pedro has been studied extensively. Flows in this river are known to depend on shallow groundwater. Because the San Pedro and its riparian corridor are unique, stakeholders generally agree that these resources are worth preserving. In 1988, Congress designated 36 miles along the river, from the Mexican border extending almost to Benson, as a National Conservation Area.
Pumping in the basin has decreased over the past decade in response to conservation measures and the retirement of irrigated agriculture. Nonetheless, monitoring data show that baseflows have continued to decline in the San Pedro River. The causes include groundwater pumping for municipal supply, the ongoing drought, and the growth and expansion of riparian vegetation. Future population growth will put additional pressures on the basin’s limited water resources.
Earlier this year, ADWR issued a “designation of adequate water supply” for the proposed Tribute development in Sierra Vista. The development’s future water use is estimated to be nearly 5,000 AF/year, which would increase current groundwater pumping in the basin by about 30 percent. ADWR states that because the applicant demonstrated that the water is continuously, legally, and physically available for 100 years, it was required to issue the permit under state law. ADWR did not consider the impacts of pumping on surface water flows or on riparian and aquatic species because state statutes do not grant it authority to do so.
In response (and following an administrative law judge’s decision upholding ADWR’s authority), a coalition of environmental groups and the BLM filed an appeal in Arizona Superior Court. The plaintiffs claim that in issuing the permit, ADWR is interfering with the conservation area’s federally reserved water rights by allowing the depletion of the aquifer that supports the San Pedro River. Citing evidence that groundwater pumping is a major cause of declining streamflow, the suit claims that water for the development is not, in fact, “legally available” to the applicant. This claim cuts right to the heart of Arizona water law.
The stakes are high, both for protection of the river and for the future of Sierra Vista and Fort Huachuca. Furthermore, this case may serve as a precedent for federal lands with water rights that are unprotected by state laws. For these reasons, the ultimate outcome (which we are unlikely to see for a long time) certainly has the potential to shake up water governance in Arizona.