DEEP-KARST AQUIFER SPRING FLOW TRENDS IN A WATER LIMITED SYSTEM, GRAND CANYON NATIONAL PARK

It is imperative to better characterize Grand Canyon National Park (GRCA) water resources to inform management decisions regarding proposed intake from Bright Angel Creek (BAC), forecast water security related to climate change, and forecast the impact on springs-dependent species. Characterization of the water supply for GRCA was improved through multi-year 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. Comparisons of snowmelt response timing and snowmelt recession coefficients among the five springs show no significant differences, indicating similar timing of snowmelt discharge and flow regimes across 50 km of horizontal and 1000 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, with the exception of the return to baseflow at Emmett Spring occurring later in the water year and 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 a need for accuracy improvements of modeled precipitation and evapotranspiration data. Continued hydrograph comparisons, trend analyses, and water budgets for additional years and springs will be useful for future groundwater modeling and forecasting impacts on the R-aquifer.