Spatial uncertainty analysis of the saturated soil hydraulic conductivity in a subtropical watershed

The high spatial variability of the saturated soil hydraulic conductivity (Ksat) and the effort required for its data sampling have been a challenge for soil scientists to obtain its representativeness at a scale resolution required by watershed management. The objective of this work was to simulate the spatial variability of Ksat and evaluate its uncertainties through sequential Gaussian simulation (SGS) in a subtropical watershed, Southern Brazil. Ksat data were obtained in an experimental grid of 179 points established in a watershed with shallow soils and relief varying from undulating to strong undulating. Experimental and theoretical semivariograms were calculated and the SGS was used to generate 100 equiprobable fields. Local and spatial uncertainties of Ksat were assessed. Lower Ksat uncertainty estimates were found in densely sampled areas. Higher Ksat uncertainty estimates were obtained in soils located at steeper areas of the watershed and on soils formed alongside the main watercourse. Spatial variability maps of Ksat are quite useful for supporting hydrological simulation of the floods in watersheds, identifying areas more prone to groundwater recharge and the effects of different tillage systems on soil water dynamics at watershed scale as well.