THREE-DIMENSIONAL GROUNDWATER MODELING OF THE REDWALL-MUAV AQUIFER ON THE KAIBAB PLATEAU, NORTH RIM OF THE GRAND CANYON, ARIZONA, BASED ON NEWLY COLLECTED DATA SETS

The Redwall-Muav aquifer, a karstified carbonate aquifer, discharges through large springs in Grand Canyon. Most of the large springs discharge from the North Rim and include Roaring Springs, the sole municipal water supply for Grand Canyon National Park. Roaring Springs supplies water to over 4 million annual visitors and year-round employees while providing significant perennial baseflow to Bright Angel Creek, a tributary of the Colorado River. Roaring Springs falls under federal water supply regulations, which do not include measurements of total spring discharge. Additionally, limited attempts to date the age of the spring water have been inconclusive. Consequently, the recharge area for Roaring Springs has never been delineated. Since the early 1970’s, the total daily discharge, pH and turbidity of water diverted from the springs (which is pumped through the trans-canyon pipeline) have been measured. In March of 2003, a temporary stream gaging station was established with a pressure transducer in the stream channel below Roaring Springs. Discharge was measured on a monthly basis through the summer monsoon, and a stage-discharge curve was constructed to allow the interpolation of spring discharge. Daily spring discharge was compared to daily turbidity, allowing for the extrapolation of spring discharge for previous years. In addition, monthly water samples were collected for d¹⁸O/d²H and tritium analysis in order to better understand recharge rates and groundwater flow paths. These data, combined with improvements in Grand Canyon geologic maps, were used to refine a 1970’s two-dimensional numerical groundwater flow model of the Redwall-Muav aquifer on the Kaibab Plateau. This new three-dimensional numerical groundwater model incorporates new data including: geologic maps, oil and gas exploration well logs, spring discharge data, and the results of geochemical analysis. The final model was displayed with a GeoWall (a digital three-dimensional projection system designed for classroom presentations) to test its applicability for hydrologic education.