Water Resources Research Act Program

Details for Project ID 2015AZ540B

Water Sources Over Time for a Semi-Arid River- Implications for Water Resources and Groundwater Modelling

Institute: Arizona
Year Established: 2015 Start Date: 2015-03-01 End Date: 2016-02-28
Total Federal Funds: $9,985 Total Non-Federal Funds: $20,604

Principal Investigators: Thomas Meixner, Steve Leavitt, Kiyomi Morino

Project Summary: Recent results for several semi-arid rivers indicate that semi-arid rivers can derive their sustained baseflow waters from a variety of water sources including snowmelt floods, summer monsoon thunderstorm floods and mountain front recharge sources. The source of water to these semi-arid rivers has important implications for the ecosystems that derive their sustenance from sustained baseflows in the semi-arid regions of the world. The recent studies have demonstrated that traditional conceptions of semi-arid river baseflow being sustained by basin groundwater derived from Mountain System processes are not entirely true. It is an open question however whether the identified flood versus basin groundwater sources are due to a continuing natural process and recharge mechanism or whether the importance of floodwater sources is evidence of hydrologic stress on these rivers due to human land and water management practices or to climate change and variability. A way to assess what these water sources have been over time is to observe the water sources that vegetation has used over time to assess the changes in water source over the last 30-60 years. We propose to investigate the variability of water in the San Pedro River and associated groundwater system using Populis Fremontis(Cottonwood) tree rings. Using this approach as well as using available data from modern day sampling of water isotopes in the precipitation, streams and groundwaters of the San Pedro basin , we will assess how water sources have changed in the San Pedro basin over time. Additionally we will use a simple surface groundwater model to assess what the potential changes in river flows were that explain the observed water isotopes in trees. Critically we view this project as a proof of concept which if successful could lead to the use of paleohydrologic methods in assessing processes, mechanisms and management in semi-arid rivers in the southwest and around the world.