Santa Cruz AMA
The management goal of the Santa Cruz AMA is to maintain a safe-yield condition in the Active Management Area and to prevent local water tables from experiencing long-term declines. Safe-yield is defined in Statute as a long-term balance between the annual groundwater withdrawn and the annual natural and artificial recharge.
The Santa Cruz Active Management Area (SCAMA) covers 716 square miles in the Upper Santa Cruz Valley River Basin. It is principally concentrated around a 45-mile reach of the Santa Cruz River from the international border to the Continental gaging station, a few miles north of the Santa Cruz/Pima County line. Along this reach, the river is characterized as an intermittent desert stream that contains uninterrupted perennial and effluent dominated reaches. The drainage area of the Santa Cruz River upstream from Continental is about 1,680 square miles. From its headwaters in the San Rafael Valley, the river flows southward approximately 9 miles, where it enters Mexico. During its 35-mile course through Mexico, the river continues its southward flow for a short distance and then bends northward and re-enters Arizona 5 miles east of Nogales. Within the United States, the Santa Cruz River continues northward for 65 miles from Nogales to Tucson, where it continues beyond to the confluence of the Gila River.
New and innovative management tools for quantification and clarification of water rights and new sources of supply may need to be developed to achieve the AMA goals.
To meet the AMA goals, new uses of water within certain areas of the Santa Cruz AMA will need to be offset either by replenishment of water withdrawn, or through a corresponding reduction in water use by existing users. Replenishment could be achieved through a mechanism to purchase recharge credits, or, in some circumstances, by a demonstration that water pumped out of storage will be naturally recharged. Reduction in existing use could be achieved by discontinuing existing water use in the same local areas in which a new demand begins. Water that is conserved through increased efficiency could, in part, be taken up by a new use.
International Water Issues
The international nature of the Santa Cruz AMA's water resources requires binational coordination of water management efforts. The Santa Cruz River is one of the main water supply sources for Nogales, Sonora and for Nogales, Arizona. The water management policies of Nogales, Sonora, in regard to the use of the Santa Cruz River, may have a direct impact on the volume of water entering the Santa Cruz AMA. Additional pumping of Santa Cruz River well fields in Nogales, Sonora could reduce both small flood flows and sub-flow, thereby reducing the recharge in the Santa Cruz AMA.
The City of Nogales and Rio Rico are the two biggest water users in the municipal sector.
Greater development pressure may come from the north, as the expansion of existing development in the Green Valley area proceeds toward the south. This development is already at the northern boundary of the Santa Cruz AMA and is expected to continue.
Development of Assured Water Supply Criteria
A future effort will be to establish Assured Water Supply (AWS) Rule criteria for evaluating the statutory requirement that issuance of an AWS certificate must be consistent with AMA goals. In order to develop the appropriate criteria, it is necessary to have a better understanding of: (1) the impact of diversions at specific locations of the subflow water levels; (2) the impact of the effluent introduced into the system and its long-term availability; (3) how effluent, surface water flows, and mountain-front recharge affect shallow aquifer water levels; and (4) a formal determination of the nature, validity, and priority of surface water rights in the context of their usage in supporting an AWS determination.
Adoption of AWS criteria specific to the Santa Cruz AMA will reflect community and stakeholder input to the highest degree possible.
The hydrogeologic characteristics of the aquifers in the Santa Cruz AMA and their close relationship with surface water flow present a challenge to augmentation and recharge that needs to be addressed with innovative approaches. Effluent discharge from the Nogales International Wastewater Treatment Plant (NIWWTP) is a major source of recharge in the AMA, and it is a significant source of water available to support future AWS determinations. Additionally, the effluent plays a major role in maintaining water tables and riparian habitat in the Younger Alluvium downstream of the NIWWTP.