Soil Water Movement and Recharge Through Sand at a Semiarid Site in New Mexico

A semiarid site near Socorro, New Mexico, has been instrumented with tensiometers and a neutron probe access tube to study soil water movement which may contribute to areal groundwater recharge under natural conditions. During the period of record which extends from November 1982 through May 1984, annual precipitation was approximately 17.9 cm yr−1. Below a depth of about 30 cm, pressure head ranged from about −129 to −35 cm and moisture content varied between about 0.05 to 0.09 cm3cm−3. The vertical hydraulic gradient was slightly greater than unity and indicated downward soil water movement. Unsaturated hydraulic conductivity was determined in the field by the instantaneous profile method. Recharge was calculated from Darcy's equation using in situ pressure head data below the root zone, calculated hydraulic gradient, and in situ hydraulic conductivity. Recharge was also calculated as being equal to the unsaturated hydraulic conductivity corresponding to in situ water content. Both approaches indicate that the annual recharge rate may be as much as about 3.7 cm yr−1, or about 20% of mean annual precipitation during this period of record.