The soil water characteristic is a measure of how tightly water is held in the soil matrix in the unsaturated state.  The soil water characteristic is a basic soil property which is second in importance to only hydraulic conductivity in modeling soil water movement.  It is usually determined in the laboratory using tension tables or pressure plates.  Several values should be obtained between 0 tension and bar (cm), with the greatest concentration of values between 0.0 and 150 cm, for example at 0 cm head, 20, 50, 100, 150, 300, 500, 1,000 and 15 bar.

 

Soil water characteristic (THETA, cm3/cm3) values are entered for the top layer of the soil profile along with the corresponding negative pressure head (HEAD, cm) in the Soil Water Characteristic tab of the Soil input screen.  The last value of the pressure head should be -1000 cm or less; i.e. a larger negative number.