Book Description

The 280-square-mile lower Tonto Creek basin is in the Central highlands water province of central Arizona. The basin is drained by Tonto Creek, which flows southward and discharges into Roosevelt Lake. The mountains that border the basinare composed chiefly of igneous and metamorphic rocks, and the basin is underlain by more than 2,000 feet of unconsolidated to semiconsolidated sedimentary deposits. The channel and flood plain of lower Tonto Creek are underlain by as much as 65 feet of alluvium. In the lower Tonto Creek basin the principal sources of water are the precipitation, which ranges from 17 to more than 20 inches per year, and the streamflow that enters the area from the upper Tonto Creek basin. The precipitation that falls on the lower Tonto Creek basin produces about 20,000 acre-feet per year of streamflow. The streamflow that enters the lower basin from the 675-square-mile upper basin is measured at the northern end of the study area and averages about 80,000 acre-feet per year. An estimated 17,000 to 20,000 acre-feet of streamflow infiltrates annually into the highly permeable alluvium. The alluvium is the principal aquifer in the lower Tonto Creek basin. Water levels in wells drilled in this aquifer rise quickly in direct response to floodflow in Tonto Creek, which indicates that a large part of the flow loss is recharged to the ground-water reservoir. In the lower Tonto Creek basin water is discharged to Roosevelt Lake by streamflow and subsurface flow and to the atmosphere by evapotranspiration. The flow from Tonto Creek that enters Roosevelt Lake averages about 80,000 acre-feet per year, the subsurface flow that enters the lake from the alluvium averages about 4,000 acre-feet per year, and the evapotranspiration losses average about 13,000 acre-feet per year. Flow in Tonto Creek and ground water in the alluvium and the lower part of the basin fill are of excellent chemical quality and are suitable for most uses. The chemical quality of ground water in the alluvium and that of flow in Tonto Creek is similar because the alluvium receives most of its recharge from the creek. Water from a well drilled in the fine - grained facies of the upper part of the basin fill is unsuitable for drinking purposes.