SPRING HYDROGRAPH AND RECESSION CURVE ANALYSIS OF EXTREME WEATHER FOR ROARING SPRINGS, IN DEEP KARST R-AQUIFER OF THE GRAND CANYON

Buried deep within the Kaibab Plateau of the North Rim of the Grand Canyon, the Redwall-Muav aquifer (R-aquifer) is a well-developed karst system that allows for quick response to extreme weather events occurring over 1,000m above. As observed through constructed spring hydrographs and recession curve analysis, the majority of R-aquifer recharge occurs in pulses following snowmelt, making it particularly vulnerable to extreme weather.

The R-aquifer is a thick, karstic system (up to 400m) consisting of Redwall Limestone, Muav Limestone, and lenses of Temple Butte Dolomite. Through sinkholes, faults, and fractures in a separate and partially disconnected karst aquifer above, it is recharged mostly by snowmelt, and to a lesser extent by extreme summer monsoon events. Past studies have shown that recharge can be rapid through large dissolved conduits in the karst, implying short aquifer residence times for extreme precipitation responses. Groundwater is then discharged after significant horizontal (10s of km) and vertical (>1,000m) travel at springs, which provide important oases for wildlife, and base flow for the Colorado River. Roaring Springs is the main source of potable water for both rims of Grand Canyon National Park (GRCA), supplying over 5 million visitors annually.

Despite its importance to people and ecosystems, the inner workings of the deep karst R-aquifer are poorly understood. Recent hydrological data have been collected at Roaring Springs, providing a continuous measurement of temperature, conductivity, and stage. With manual monthly discharge measurements, a new stage-discharge relationship was created including recent high flow events, to more accurately represent a spring hydrograph. High discharge peaks were evident after both snow and monsoon events. The recession curves following these peaks were analyzed to quantify the drained aquifer volume, for a better understanding of storage and transit time. With increasing uncertainty from a changing climate, water stored in aquifers is essential in dessert ecosystems with limited surface water. Understanding different flow inputs and transit time will assist in a comprehensive management plan to protect the water supply in GRCA and other karst aquifers.