Abstract
The Colorado River supplies water to more than 50 million people, irrigates 4 million acres of cropland in the U.S. and Mexico and serves as the source for hydropower plants generating a total of 10 billion kilowatt-hours per year. Groundwater is an integral component of the hydrologic system supporting this vastly relied upon water supply (Miller et al. 2016). Groundwater enters hydrogeologic units at the ground surface and eventually discharges to the river through springs in the canyon walls. Water from the Upper and Lower Colorado River basins is depended on by residents of Wyoming, Utah, Colorado, New Mexico, Arizona, California and Mexico and is the most over-allocated river in the world (Christensen et al. 2004; Miller et al. 2016). Projections show that demand could exceed supply by 4 billion cubic meters by 2060. On a smaller scale, water from a single groundwater-sourced spring in Grand Canyon National Park supported 6.3 million of the Park’s visitors in 2017. Annual visitation is projected to double by 2050 (Bureau of Reclamation 2002), which will intensify the strain on the National Park’s groundwater resources. Recent development of areas overlying the Grand Canyon’s major aquifers has increased the demand for groundwater pumping which has resulted in declining groundwater levels and spring discharge. Many people consider springs to be culturally significant, including some local Native American tribes. Springs are generally appreciated for their aesthetics and support up to 500 times as much species diversity as the non-spring environments surrounding them. Water managers are continually pressured to increase water availability by proposed tourism-related development. Development causes increases in water demand that may not be feasible considering the region’s hydrologic setting. Climate change is an impending threat to the consistency of the Colorado River Basin’s water supply. Some projections estimate that with current operating policies, average reservoir storage in the Colorado River Basin will decrease by 40% by 2098 (Christensen et al. 2004). Due to the ecological and anthropogenic sensitivity to the Colorado River Basins’ groundwater, management decisions should be made with the utmost care and consideration of the potential for a once-sustainable hydrologic resource to become inadequate in meeting anthropogenic and ecologic needs.