Hydrologic Model for Water Resources Planning in Arid Southern Arizona.

Eylon Shamir

Hydrologic Research Center

A set of hydrologic models for the southern region of the Santa Cruz River was developed as a water resources management and planning tool for the Santa Cruz Active Management Area (SCAMA). These models are utilized in conjunction with groundwater models that have been developed by the Arizona Department of Water Resources as a probabilistic tool to determine safe and reliable levels of groundwater development in the SCAMA. The models consist of: 1) a stochastic model of hourly precipitation scenarios that maintains the characteristics and variability of a 45-year hourly precipitation record from a near by raingauge; 2) a process based conceptual model that transforms the precipitation into daily streamflow using varied infiltration rates and estimates the basin’s antecedence moisture conditions; and 3) a simplified groundwater model for four microbasins downstream the gauge that accounts for alluvial groundwater recharge, and ET and pumping losses. To maintain the large inter-annual variability of flow as prevails in Southern Arizona, the model is constructed to produce three types of seasonal winter and summer regimes of flows (i.e., wet, medium or dry season).

Long term (i.e., 100 years) realizations (ensembles) are generated by the above described model that reflects two different regimes. The first regime is that of the historic rain gauge record. The second regime is a paleoclimatic reconstructed precipitation regime derived for this location from tree-ring data. These two ensembles are used to evaluate the risk the four microbasins to decline below a storage threshold that represents an aquifer stress under different operational schemes. The risks of both the frequency and the consecutive occurrences of aquifer storage to drop below a given threshold were evaluated under different monthly pumping scenarios.

Acknowledgments: Support for this work was provided by Arizona Department of Water Resources (ADWR) Santa Cruz Active Management Area under contract # 2005-2568. Special thanks are extended to the ADWR personnel Frank Corkhill, Gretchen Erwin, Keith Nelson and Alejandro Barcenas for collaboration in data interpretation and research direction.