Rainfall infiltration characteristics for a semi-arid watershed soil

Abstract

Rainfall infiltration characteristics for a semi-arid watershed soil were studied. The soil examined was obtained from Page Ranch, 25 miles north of Tucson, Arizona. Laboratory infiltration tests were conducted on reconstructed soil profiles similar to those on the watershed. A mathematical model of infiltration, developed by Dr. Roger Smith, was used to simulate the infiltration process. Results from infiltration tests conducted on site at the watershed during a previous research study were also simulated using the infiltration model. Laboratory and field infiltration tests were conducted using a realistic rotating disk rainfall simulator. Single- and dual-source gamma ray attenuation techniques were used to obtain soil moisture measurements within the laboratory soil profiles. Direct measurement of surface crusting effects in the laboratory using the dual-source technique was attempted but was determined to be unworkable due to resolution and boundary effect problems. Using the measured saturated hydraulic conductivity values of the laboratory and field soils, and the unsaturated soil properties as measured for the field soil, the mathematical model of infiltration as developed by Dr. Roger Smith simulated the infiltration rates of bare test plots. By changing the saturated conductivity of the upper soil layer, it was also possible to simulate the infiltration process on a grass-covered field plot.