VARIABILITY OF UNSATURATED ZONE WATER TRANSPORT PARAMETERS - IMPLICATIONS FOR HYDROLOGICAL MODELING .2. PREDICTED VS IN-SITU MEASUREMENTS AND EVALUATION OF METHODS

Two methods to estimate the saturated and unsaturated hydraulic conductivity of soil were compared in a catchment in south-west England. The catchment consists of three land use domains - arable, permanent grass and woodland. The methods used were in situ measurements using a Guelph permeameter and the predictive model of Rawls and Brakensiek, which uses percentage of sand, percentage of clay and porosity as input. In grassland and woodland no significant differences were found between the mean saturated and unsaturated hydraulic conductivity estimated by the two methods. It is suggested that a significant difference found for the arable land is due to the effect of farming operations on soil permeability. On a catchment scale there were no significant differences between the methods. The results obtained using the predictive model are encouraging and worth further investigation. The advantages and disadvantages of the two methods are evaluated.