Post‐Irrigation Movement of Soil Water: 1. Redistribution

Water content measurements by γ‐ray attenuation in soil columns were made during redistribution following irrigation. Approximate solutions of the unsaturated flow equation are derived that describe the water content above the initial wetting front as a function of time. For times sufficiently large, these solutions reduce to the frequently used empirical expression W = a t^−b, where W is soil water content, t is time, and a and b are constants. These constants can thus be related to the capillary conductivity and soil water diffusivity.