In situ characterization of preferential flow by combining plot- and point-scale infiltration experiments on a hillslope

This study focuses on the identification of the lateral preferential flow at the hillslope scale and the estimation of the saturated hydraulic conductivity for the fast-flow region, Ks,f, based on infiltration experiments carried out at different spatial scales (point- and plot-scales), and at different soil depths. The discrepancies between the considered scales were mainly attributed to macropore flow and the difficulty in adequately embodying the macropore network on small sampled soil volumes. Conversely, at the plot-scale, the sampled volume was sufficient to activate the macropore network. This information helped establish the usability of a given technique to determine the parameters describing the hydraulic properties of the soil in the matrix and fast-flow regions. While Ks data obtained from the Beerkan method with the Beerkan Estimation of soil Transfer (BEST) parameter algorithm (point-scale) were used to describe the matrix (Ks,m), the saturated hydraulic conductivity for the fast-flow region was estimated using the soil block method (plot-scale). Estimated Ks,f values were one to three orders of magnitude higher than Ks,m. The overall decrease of Ks,f with the soil depth supported the hypothesis that the macropore density decreased as a function of depth, yielding higher macropore flow variability. The soil block method, in association with the Beerkan infiltration runs, allowed the estimation of the saturated hydraulic conductivity for the fast-flow region based on a relatively simple field procedure.