Using Isotopes And Modeling To Determine Effects Of Rock Dams On Infiltration
Presenter: Diana Hsieh1
Advisor(s): Dr. Ty Ferre
1Department of Hydrology and Atmospheric Sciences, University of Arizona
Groundwater resources are under stress due to increased pumping observed in an increasingly arid American southwest. One possible mitigation strategy is the use of rock dam detention structures, which slow the flow of water and promote recharge beneath ephemeral springs. However, it is unclear whether these structures increase recharge at larger scales. Using HYDRUS 1-D, different soil compositions, rain events, and initial conditions will be modeled to determine the theoretical magnitude and timing of recharge that allow for recharge. If upon modeling it is determined that recharge is likely, then transducer data from a nearby monitoring well will be used to characterize the timing and rate of recharge. This information will also allow us to determine whether any recharge is rapid enough to result in physical mounding of groundwater at the rock dam. Additionally, groundwater and surface water samples were collected during the recent summer monsoon and analyzed for major anions and cations, stable water isotopes (δ18O and δD), and tritium (3H). These data will be used to determine the source, flowpaths, and residence times of the water. With this data we will be able to determine whether the groundwater near the rock dam contains monsoon precipitation and whether recharge occurred. The combination of the above mentioned data will be able to provide a more complete picture of the effectiveness of rock dams, and how best to use them to mitigate drawdown of groundwater.