Deep-karst aquifer spring-flow trends in a water-limited system, Grand Canyon National Park, USA

Better characterization of the water resources of the Grand Canyon National Park (GRCA) and World Heritage Site, USA, will inform management decisions regarding a proposed water supply intake from Bright Angel Creek (BAC) and will inform the associated forecasts on water security related to climate change and the impact on spring-dependent species. Characterization of the water supply for GRCA was improved through multiyear hydrograph analyses at five springs discharging from the Redwall-Muav (R) aquifer: Roaring Springs, Emmett Spring, At Last Spring, Tapeats Spring, and Abyss River Spring. Comparison of snowmelt response timing and mean recession coefficients among the five springs show no significant differences, indicating similar timing of snowmelt-related discharge and flow regimes across 50 km of horizontal and 1,000 m of vertical distance through the aquifer system. The mean water volumes discharged during snowmelt and the mean annual discharge are significantly different between Roaring Springs, Emmett Spring, Tapeats Spring, and Abyss River Spring. Linear regression analyses indicate no annual trends in any of the evaluated aquifer characteristics for any spring, except for more stable baseflow between recessions at Tapeats Spring. Water budgets calculated for Roaring Springs are imbalanced, suggesting missing outflow components, a need to refine the recharge region through dye trace studies, and inaccurate precipitation and evapotranspiration data, requiring model improvement. Continued hydrograph comparisons, trend analyses, and water budgets for additional years and springs will be useful for future groundwater modeling and for forecasting impacts on the R aquifer.