The hydro-mechanics of the ground water system in the southern portion of the Kaibab Plateau, Arizona

Abstract

The elevated Kaibab plateau in northern Arizona has an area of 88 0 square miles and lies adjacent to the Grand Canyon of the Colorado river. It is composed of a sequence of lithified Paleozoic rocks that are approximately 4000 feet thick and consist of marine sediments that contain very little permeability. The ground water system of the plateau has two principal components: 1) circulation through unfractured stratified rocks that range up to a few tens of miles wide and 2) fault controlled drains. In unfractured zones, most of the ground water circulation takes place in the upper 900 feet of the section. The water drains laterally through these rocks toward fault zones or seep faces along the canyon walls. Approximately 40 percent of the plateau surface (330 square miles) drains to canyon seeps. Fault zones provide laterally and vertically continuous large capacity conduits through the plateau. These function as drains for the ground water system as well as floodways for storm pulses that enter the faults directly from the surface. Fracturing has controlled the development of extensive karst networks in limestones that lie near the base of the Paleozoic section. These systems drain to 10 groups of karst springs that discharge an average of approximately 100 cubic feet of water per second. The karst springs drain approximately 60 percent of the plateau surface (550 square miles). The springs in Tapeats amphitheater on the west side of the plateau discharge from the extensive West Kaibab fault zone and account for approximately 70 percent of the measurable water leaving the plateau. This group of three springs drains about 40 percent of the plateau surface (380 square miles). Development of ground water supplies does not appear to be economically tenable in the unfractured portions of the plateau because the permeabilities of the rocks are very small and the depth to the small quantities of available water exceed 500 feet. Production from the large fault controlled drainage networks is equally unattractive. Although the occurrence of water is certain, the large supplies are more than 2800 feet below the land surface and exist in finite channels along the fault zones. These would be difficult to penetrate with conventional drilling methods.