SOIL-WATER DIFFUSIVITY DETERMINATION BY GENERAL SIMILARITY THEORY

A new and simple method is presented for estimating soil water diffusi vity. This method utilizes general similarity theory rather than the B oltzmann transformation to evaluate horizontal water infiltration-redi stribution processes, It uses the Brooks and Corey function of water d iffusivity and requires only measuring the wetting front advance with time, General similarity diffusivities for five soils were compared wi th those obtained by the Boltzmann transformation and with a third met hod that used a fitting function to approximate the water distribution data in the Boltzmann transformation method, The comparisons showed t hat soil water diffusivities for the three methods were in good agreem ent for the intermediate range of water contents, However, at low wate r contents the similarity water diffusivities differed from the other water diffusivities for the five soils, The new method has several adv antages over the other methods. It allows the inlet boundary water con tent to vary in time and initial water content distribution to vary wi th distance, which is more general than constant water content, The ne w method also does not require soil water diffusivity to be zero at th e initial water content. This represents an improvement over the earli er methods, which give a zero diffusivity at initial water content no matter how high this initial water content is.