SUSTAINABILITY OF THE GRAND CANYON NATIONAL PARK SPRING WATER SUPPLY

The quantification of the long-term sustainability of the current water supply for Grand Canyon National Park (GRCA) was improved through new hydrograph recession analyses on precipitation events from 2017—2020 from two major springs: Roaring and Emmett Springs. The potable water supply at GRCA is currently sourced entirely from Roaring Springs, which discharges from a cave in the Redwall-Muav (R) aquifer on the north side of the canyon and into the perennial Bright Angel Creek (BAC). As GRCA management develops new plans for potable water intake from the BAC system, it is imperative to characterize the current water supply and forecast future water security of R aquifer water sources. A modified Maillet equation for exponential curve fitting is used to calculate fitted curves and recession coefficients (a measure of change in discharge over time) for recession events. The method was applied to the Roaring and Emmett Springs hydrographs based on an updated stage-discharge relationship and additional events to those analyzed in 2017. These new recession coefficients were evaluated with those calculated from two previous hydrologic years and with tracer studies used to isolate groundwater flow paths from source to spring. Preliminary recession analyses for Roaring Springs yielded recession coefficient (α) values of the same order of magnitude as previous measurements, though the lengths of the recessions were variable. The average volume (V) discharged for any given snowmelt event from 2015 – 2019 was calculated to be 3.8 + 1.9 x m³. Further studies will include more events in the calculation of α and V and quantitative inflection point selection on recession curves for more accurate identification of aquifer flow paths.