Importance of river water recharge to the San Joaquin Valley groundwater system

Abstract

Groundwater is not a sustainable resource, unless abstraction is balanced by recharge. Identifying the sources of recharge in a groundwater basin is critical for sustainable groundwater management. We studied the importance of river water recharge to groundwater in the south‐eastern San Joaquin Valley (24,000 km2, population 4 million). We combined dissolved noble gas concentrations, stable isotopes, tritium, and carbon‐14 analyses to analyse the sources, mechanisms, and timescales of groundwater recharge. Area‐representative groundwater sampling and numerical model input data enabled a stable isotope mass balance and quantitative estimates of river and local recharge. River recharge, identified by a lighter stable isotope signature, represents 47 ± 4% of modern groundwater in the San Joaquin Valley (recharged after 1950) but only 26 ± 4% of premodern groundwater (recharged before 1950). This implies that the importance of river water recharge in the San Joaquin valley has nearly doubled and is likely the result of a 40% increase in total recharge, caused by river water irrigation return flows and increased stream depletion and river recharge due to groundwater pumping. Compared with the large and long‐duration capacity for water storage in the subsurface, storage of water in rivers is limited in time and volume, as evidenced by cold river recharge temperatures resulting from fast infiltration and recharge. Groundwater banking of seasonal surface water flows and expansion of managed aquifer recharge practices therefore appear to be a natural and promising method for increasing the resilience of the San Joaquin Valley water supply system.

Characterization of Groundwater Recharge and Flow in California's San Joaquin Valley From InSAR‐Observed Surface Deformation

“…In fact, all winter uplift features on the eastern side of the valley (e.g., P w 2, P w 4, and P w 6) are associated with lower δ 18 O concentrations. While we do not observe a similar, distinct winter uplift feature along the Kings River, the region of lowest δ 18 O content in the Visser et al (2018) study, this could be due to the perennial nature of the Kings (i.e., recharge occurring with more regularity rather than just seasonally) and that the coarser-grain material underlying the region is less susceptible to high-amplitude deformation related to changes in pore pressure. The agreement between these two independent data sets underscores the potential utility of these new observations of uplift timing and evolution as a tool for understanding groundwater recharge and flow.…”

“…Water with a relatively lighter isotopic signature (depleted in the heavier isotopes) is then channeled and transported into the SJV by Sierra-sourced rivers. Visser et al (2018) found plumes of depleted δ 18 O concentrations in groundwater samples originating near the Kings, Kaweah, Tule, and Kern Rivers (their Figure 4b), emphasizing the role that these rivers play in the recharge of the aquifer system. In fact, all winter uplift features on the eastern side of the valley (e.g., P w 2, P w 4, and P w 6) are associated with lower δ 18 O concentrations.…”

Combined Impacts of Uncertainty in Precipitation and Air Temperature on Simulated Mountain System Recharge from an Integrated Hydrologic Model

“…In our simulations, the majority of this recharge comes from the MFR pathway, the ratio of MFR/(MBR + MFR) ranges from 0.85 to 0.99 across all simulations performed. Our results are consistent with observational studies (Visser et al, 2018), but there is considerable uncertainty related to characterizing the source of mountain system recharge. The simulated MFR depends on the subsurface permeability values assigned to the Central Valley aquifer in the piedmont slope region.…”

Global Isotope Hydrogeology―Review

“…Still other works have identified river waters that have been diverted for irrigation as important recharge sources (e.g., Bajjali, ). In California's Central Valley, river‐borne recharge has been identified in well waters with large proportions of recent recharge, signifying irrigation practices generate recharge (Visser et al, ; see also Criss & Davisson, ). In other aquifer systems underlying heavily irrigated lands, isotopic data show that irrigation return flows more likely derive from intensive groundwater‐fed irrigation than from diverted river waters (e.g., North China Plain—von Rohden et al, ; Sbeïtla Aquifer in Tunisia—Dassi, ; and portions of California's Central Valley—Davisson & Criss, ).…”