Depletion of streamflow by infiltration in the main channels of the Tucson basin, southeastern Arizona

Abstract

Estimates were made of the average annual volume of infiltration for the period 1936-63 along seven normally dry alluvial channels in the Tucson basin. The essential parts of the method used to estimate infiltration were (1) average relation between rates of inflow and infiltration and (2) flowduration curves of streamflow. The end product is an infiltration-duration curve from which the average annual volume of infiltration may be computed. The general empirical relation between inflow rates and infiltration rates for a reach of channel is infiltration rate=C (inflow rate) °-8 , in which C is a variable coefficient. In this report an average coefficient was determined or estimated for all flow moving through a given reach of channel. The equation is used in estimating the infiltration rate only when the inflow rate is greater than the computed infiltration rate. Estimates of flow duration for ungaged streams were derived from simple relations between measured daily streamflow and size of contributing basin for flow that is equaled or exceeded 0.1, 0.5, 2.0, and 10 percent of the time. The degree of correlation between measured streamflow and size of basin is fair for flows of rare occurrence but decreases with more common flows. The main channels in the Tucson basin are efficient natural infiltration galleries. The average annual streamflow depletion ranged from about 30 to 90 percent of the average annual inflow to the seven reaches for the period 1936-63. The average annual inflow to all the reaches was about 66,000 acrefeet ; of this about 47,000 acre-feet, or 70 percent, was depleted by infiltration, and about 19,000 acre-feet flowed out of the basin. The annual variation in infiltration volumes along the main channels is large and is mainly the result of variation In streamflow. On the basis of streamflow data, the extremes in the annual volumes of infiltration are estimated to range from near zero to more than four times the average annual volume. INTRODUCTION Inhabitants of the Tucson basin (fig. 1) are dependent entirely on ground water for their water supply. Since 1940, there has been