MODELING THE WATER SUPPLY OF GRAND CANYON NATIONAL PARK—THE EFFECT OF CLIMATE CHANGE ON A KARSTIC AQUIFER

Roaring Springs is the sole water source for Grand Canyon National Park’s approximately 4.8 million annual visitors and 2100 residents, however, little is known about the behavior and character of the karst aquifer that drains through the spring complex. In the face of climate change (predicted increases in aridity and a shift from snow to rain), increased development, and potential contamination, it is essential to characterize the aquifer in order to both conserve downstream aquatic and riparian ecosystems and to manage the park’s water supply. Additionally, estimating the storage capacity of the aquifer allows the park to begin adjudication processes to claim and protect its water, ensuring better protection of the Canyon’s ecological resources.

To better understand the capacity, retention time, and flow paths of the aquifer we conducted hydrograph analyses, including recession analyses and hydrograph separations, and performed the first dye trace study in Grand Canyon National Park. Hydrograph analyses of 2013 and 2014 data show an approximate 18 percent reduction in both total annual discharge and total baseflow storage between 2013 (a dry year with winter snowpack) and 2014 (a dry year with minimal snowpack). However, baseflow recession slopes remains constant between years. Hydrograph separations show an initial piston flow pulse dominating early snowmelt while direct flow dominates remaining snowmelt input. These results indicate that increasing aridity reduces aquifer storage and show a relatively short retention time within the aquifer system. These trends suggest that this aquifer and associated downstream ecosystem may be vulnerable to significant reduction in flow in the face of climate change