Water intake at the atmosphere-earth interface in a fractured rock system near Patagonia, Arizona

Abstract

Surface water intake into a fractured rock system provides water for downward percolation and transport of contaminants. This study involves the measurement and simulation of water intake across the atmosphere-earth boundary, for an exposed densely welded tuff, near Patagonia, Arizona. Water and air intake rates were measured using a fractured rock infiltrometer (FRI). Calculated fracture apertures using water and air agreed Well. Fracture apertures determined using water range from 1.0 to 33.7 pm and are shown to be log-normally distributed. Rainfall events are reconstructed in a model to simulate flow across the atmosphere-earth boundary. As an example a ten-year simulation resulted in a mean annual intake rate of 2.1 millimeters (mm), and is shown to be more dependent on storm duration than intensity. Developed methods provide a means of characterizing water intake rates into a fractured rock surface based on rainfall characteristics.