DELINEATION OF SOURCE WATER PROTECTION AREAS FOR TRIBAL WATER SUPPLIES, KAIBAB PAIUTE RESERVATION, ARIZONA

The 490,0002 km Kaibab Paiute Reservation is located on the Arizona Strip, a semiarid geographical province between the North Rim of the Grand Canyon and the southern border of Utah. The hydrogeological framework of the reservation is dominated by the generally south striking, west dipping Sevier-Toroweap fault, which bisects the area into two distinct groundwater systems. West of the fault, the groundwater system is controlled by a densely fractured zone in the Jurassic Navajo Sandstone aquifer where historical springs reportedly discharged as much as 19 l/sec . East of the fault, the conglomeratic Shinarump member of the Triassic Chinle Formation is the principal water-bearing unit from which only small locally recharged springs discharge.

Within the study area, water management is complicated because there are multiple land owners of the aquifer: the National Park Service at Pipe Spring National Monument, a private inholding within the reservation boundaries at the Mormon settlement of Moccasin, the Kaibab Paiute Tribe, and the adjoining states of Arizona and Utah. In an effort to assess the potential risks and benefits of taking over jurisdiction of its own water supply, the Kaibab Paiute Tribe began to implement a Source Water Assessment Program (SWAP). This study helped define capture zones of the various water sources for the SWAP.

A three-dimensional finite-difference groundwater flow model of the Kaibab Paiute Reservation was created and capture zones were delineated for each water source. The model was initially calibrated to historical conditions from 1965 to 1976 when the first wells were drilled in the area. Data for the unstressed static water levels at the time of drilling are available over this period. Results show that 85% of recharge to the aquifer within the reservation boundaries is not used by the tribe, of which 60% flows into Utah due to gradients and groundwater divides. This pre-development simulation of the aquifer provides valuable insight into the historical interactions of recharge and the groundwater flow system before any of the public and private stakeholders began withdrawing water from the aquifer.