Paper No. 185-1
Presentation Time: 8:15 AM
INNOVATIVE SPATIAL AND TEMPORAL MEASUREMENTS OF RECHARGE TO THE DEEP AQUIFERS OF THE GRAND CANYON REGION
The Colorado Plateau is comprised of multiple stacked aquifers, some of which have depths to water exceeding 1,000 m below land surface. Recharge to these deep, regional aquifers supplies springs discharging in the Grand Canyon and adjoining areas. Previously, recharge has only been determined with annual or decadal water balance estimates and approximations from numerical modeling techniques. Ongoing studies seek to observe and measure the temporal and spatial variability of recharge in this region. The climate is arid to semi-arid. Winter precipitation is typically distributed into frontal storms dominated by snow, while convective thunderstorms prevail in summer monsoon rains with dryer periods occurring in spring and fall seasons. Precipitation increases with elevation in the region. Recharge is episodic and focused through enhanced permeability faults, fractures, and dissolution enhanced features. A precipitation derived chloride mass balance study defined the seasonality of recharge by precipitation and the magnitude of recharge dependent on vegetation cover type. This study demonstrated the importance of upland vegetation management in influencing the timing and magnitude of recharge. A qualitative tracer study coupled with detailed measurements of temperature at springs emanating from the deep regional aquifers is helping to determine the locations and travel times of recharge focused in sink holes. These measurements indicated travel times of a few days from spring snow melt entering sinkholes on the surface of the Kaibab Plateau to discharge at springs over 1,000 m deep and 1,000’s of meter lateral flow. Together, these studies show that previous estimates of uniform spatially distributed, mean annual estimates of recharge in this region do not adequately reflect observation and direct measurement of recharge. These improvements in recharge measurements are laying the foundation for construction of models with better spatial and temporal resolution of recharge and improved management of limited groundwater resources.