A COMPARISON OF SOIL SURVEY METHODS IN RELATION TO CATCHMENT HYDROLOGY

Eight primary catchments within the Western Australian wheatbelt were surveyed in detail to examine the abilities of conventional soil class ification and geostatistical analysis to provide detailed information of soil spatial variation for catchment-scale hydrologic modelling. Ni ne soil physical properties were measured. The results illustrate pote ntial difficulties with both methods. Classification by using the Fact ual Key was unable to describe the major component of soil property va riation. The relative variance accounted for by soil classes was usual ly <10%. Only the yellow duplex soils appeared distinct from other soi l classes. Potential difficulties with geostatistical analysis also ar ose because of fluctuations in the variogram models. Contrasts occurre d between variograms for the same property over different catchments a nd for different properties over the same catchment. Within tile areas studied, nugget and linear (unbounded) variogram models were more com mon than spherical or exponential models. It is proposed that the surv eyor would have to select a survey method on the basis of prior knowle dge about which model of variation is more likely to be successful for the scale and location of survey.