Hydrogeological analysis of groundwater flow in Sonoita Creek basin, Santa Cruz County, Arizona

Abstract

The Sonoita Creek basin lies in a north trending intermontane valley in southeastern Arizona. Mature dissected mountains rise abruptly from long alluvial slopes and culminate in peaks ranging from 1000 to 1300 feet above the valley floor. The mountains surrounding the alluvial sediments are of volcanic rocks of Miocene ? age, and have been subjected to tectonic disturbance which resulted in extensive faulting, folding, and the formation of joint systems. The alluvial sediments have been divided into five units based on their stratigraphic position, structural involvement, lithology, and permeability. The oldest unit in the basin is unit No. 5 and the youngest is unit No. 1. Groundwater supplies of the Sonoita Creek basin are developed largely from alluvial unit No. 4, and minor supplies from alluvial unit No. 1. The groundwater originates as precipitation on the mountain areas and on the floor of the valley. The average rainfall on the valley floor is about 20 inches per year while on the mountains it is more than 50 inches per year. A minor part of the groundwater recharge is from the discharge of Monkey spring into the northern part of the basin. Groundwater is discharged from the Sonoita Creek basin through evaporation, as effluent flow of about 7 cubic feet per second through Sonoita Creek, and by artificial discharge through pumping. The perennial streamflow in Sonoita Creek near Patagonia is due to the impervious volcanic rocks in the subsurface, which crop out 500 feet south of the town, forcing the groundwater to discharge at the surface. Groundwater in the basin is generally of excellent to good quality for irrigation use, and medium to good for domestic purposes. The groundwater contains high percentages of sulphate, calcium, and bicarbonates.