HYDROGEOLOGICAL CHARACTERIZATION OF SPRINGS IN THE VERDE RIVER WATERSHED, CENTRAL ARIZONA

The demand for water resources is rapidly increasing in the Verde Valley region of Central Arizona, and the understanding of these resources is critical to the their management. Even though Arizona has the second highest density of springs of any state west of the Mississippi River, it is estimated that more than half of them are uncharacterized. These springs have a high value for the ecosystem services their water provides. The 200 springs discharging in the 7,000km2 Middle Verde River Watershed reflect groundwater conditions and surface-water contributions to the watershed. Previous studies have investigated the changes in baseflow for a few streams, but studies of the numerous smaller discharge springs are outdated or have not been done. An inventory of springs in this region was conducted to better understand them for future management. A large number of springs located in the study area between the confluence of Sycamore Creek and the Verde River to the Horseshoe Dam have been identified by physical, chemical, and ecological characteristics. These include location, discharge, basic water chemistry, geomorphology, vegetation and geology for each spring. From this inventory, a suite of springs located in different geologic formations was selected for a pilot monitoring study to understand spring discharge fluctuations and their relationship with the geology. In addition to the monitoring of the characteristics described above, stable isotope analysis of 18O and 2H will be completed once in the winter and once in the summer for each spring. Stable isotope analyses will be used to characterize the hydrogeology of different geologic formations and to determine the source of water from the aquifers influencing spring discharge. Information from this study will be useful in future studies and benefit future management of the water resources in the region.