Technical Memorandum Report No. 51
Simplified Techniques for Determining Water Conducting and Water Storage Properties of Soils
Lajpat R. Ahuja and Richard E. Green
October 1976
ABSTRACT
Four simplified methods of simultaneously determining both hydraulic conductivity and water characteristic functions of a soil from field tensiometric data for drainage were investigated. These soil-water properties were assumed to be described by certain simple power or logarithmic functional forms. Two of the function parameters were the near-saturated values of soil-water content and hydraulic conductivity, which were assumed to be known (from measurements during infiltration preceding the drainage). The other two unknown parameters were determined either by the least-squares optimization over the complete range of data, or by the algebraic manipulation of data for two consecutive time values. The latter option allowed for a change in values of the parameters in a piecemeal manner. In both cases, the Richards equation of unsaturated soil-water movement was either handled as such in the differential form or was integrated once, before functional substitutions and solutions. A cubic-spline fitting was used for finding derivatives. The schemes of computation were tested and developed on a set of test data with known input parameters, and then applied to a set of field data. The methods involving piecemeal function approximations showed good results.