Testing an adapted beerkan infiltration run for a hydrologically relevant soil hydraulic characterization

Abstract

Literature raises doubts about the usability of infiltrometer methods to characterize soils in a hydrological perspective since these methods often yield excessively high infiltration rates or saturated soil hydraulic conductivity, Ks, values. For a loam (AR) and a silty-clay (RO) soil, beerkan infiltration runs were adapted in the perspective to obtain usable soil data to predict rainfall partition into infiltration and rainfall excess. In particular, the initially nearly dry soil was sampled with different water volumes (15 or 30) and heights of water application (low, L, 0.03 m, and high, H, 1.5 m), and the BEST-steady algorithm was applied to determine sorptivity, S, and Ks. The H runs altered the surface soil layer more than the L runs but the response of the two soils to disturbance was different. For the AR soil, deterioration of the surface layer was almost complete close to the end of the run while, for the RO soil, it was concluded after applying one third of the overall used water volume. The least soil perturbing experiment (15L), that was carried out with the commonly recommended experimental protocol, yielded high S (91–118 mm/h0.5) and Ks (88–294 mm/h) values at the two sites, likely incompatible with formation of any rainfall excess. A soil perturbing experiment (30H) yielded significantly and substantially smaller S (26–40 mm/h0.5) and Ks (4–6 mm/h) values, that appeared potentially compatible with formation of rainfall excess. The gravitational potential energy, Ep, of the water used for the infiltration run explained most of the variance of both Ks and S. In conclusion, the infiltration run can be adapted in an attempt to induce a soil disturbance likely similar to that expected for a rainfall producing runoff. In a relatively dry initial status, complete deterioration can require less water for a silty-clay soil than a loam soil. The saturated soil hydraulic conductivity is more sensitive than soil sorptivity to the applied experimental methodology. Finally, the gravitational potential energy of the applied water could be used to establish a link between the hydrological process that has to be explained and a soil hydraulic characterization appropriate to reach the desired objective.