diffusivity

Accurate information concerning soil hydraulic characteristics is needed for an understanding of the process of water flow and solute transport through soils. One of the soil hydraulic characteristics is its hydraulic diffusivity in unsaturated conditions. A simple method of determining soil hydraulic diffusivity is a simple procedure in which soil moisture measurement is not required and instead only by measuring the wetting front versus time, cumulative infiltration versus wetting front as well as infiltration rate versus inverse wetting front, soil hydraulic diffusivity function can be determined. In this method, the depth of soil column affects the accuracy of the results. Therefore, in this investigation one dimensional horizontal infiltration soil column was used to determine the minimum length (depth) of soil column for three soil textures (light, medium and heavy) employing the above mentioned simple method. Results indicated that for lighter soils, a deeper column of soil would be needed. So that a minimum column length (depth) for heavy and medium soils would be 8, and 15 cm respectively, and while for a light type of soil the column length must be more than 60 cm. Mean diffusivity coefficients for soils with varied initial moisture contents and for different soil textures (in different infiltration and evaporation states) have been presented. Mean hydraulic diffusivity coefficient decreased from light to heavy soil, the same way as did the hydraulic diffusivity coefficient.