Estimating Mountain System Recharge Using Recession Flow Analysis In The Sierra Nevada, California

Abstract:

Mountainous catchments, such as the Sierra Nevada in California, play an important role in providing freshwater resources in semiarid regions. Quantifying groundwater recharge in mountainous regions is required to sustainably manage water resources. However, limited information is available about mountain system recharge processes and their rates in response to precipitation variability in the Sierra Nevada. As streamflow represents the integrated catchment response, we apply streamflow recession analysis to quantify dynamic storage changes in the subsurface. We derive seasonally distinct storage-discharge relationships in eleven undisturbed catchments throughout the Sierra Nevada, based on streamflow observations and baseflow estimates. We perform a sensitivity analysis to test the impact of multiple assumptions required to derive the storage-discharge functions. Results demonstrate that average annual recharge efficiencies (annual recharge divided by annual precipitation) in the study catchments range from 0.05 to 0.24 and 0.08 to 0.32 based on streamflow and baseflow datasets, respectively. Streamflow-derived recharge is generally lower than the baseflow-derived recharge.
A sensitivity analysis exploring the number of dry days required to start the recession analysis demonstrates that both streamflow and baseflow recharge efficiencies decrease by 0.02 per day by increase in the number of days excluded after a rain event. Results of the sensitivity analysis further illustrate that the recharge efficiency is most sensitive to the selection of number of days after a rain event to start the analysis in comparison to the baseflow separation parameters. In addition, sensitivity analysis of the Eckhardt baseflow separation algorithm demonstrates that the recharge efficiency is more sensitive to the maximum baseflow index than the recession constant parameter. Our results suggest that storage-discharge functions are useful tools to quantify groundwater recharge in mountainous catchments particularly when observational data are limited. However, the contribution of groundwater to streamflow should be meticulously analyzed given the uncertainties exist in the hydrometric observations and recession flow analysis.