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This article presents the results of an experimental study on the transportability of soil particles by runoff water in the early stages of a rainfall event. The soil under consideration comes from three ravines in the city of Antofagasta known to have been affected by detritus flow events in the past and made up of mainly cemented sands and gravels with soluble salts. A parametric study was carried out using a laboratory infiltrometer with a rain simulator with variable intensity and a soil sample also with a variable slope. With this apparatus it was possible to analyse the effect of rain intensity and slope on the progress of the wetting front, the quantity of runoff and the quantity and grading characteristics of the soil removed by the runoff. Also analysed were the grading characteristics of the soil from each ravine and their in situ densities before and after the addition of water, in order to study the changes that this can induce on the arrangement of particles when dissolution of the salt cement occurs. The results show that the grading of a soil can affect two principal aspects of its transportability. Firstly, the grading affects the capacity for infiltration of the soil and the occurrence of runoff. Secondly, it affects the in situ soil structure which in turn affects the resistance of the particles against drag forces exerted by the runoff. The study also shows that within the ranges considered, the angle of the slope did not affect the generation of runoff nor the quantity of material removed. [ABSTRACT FROM AUTHOR]

The vertical infiltration of water is a variable saturated flow process until the soil under an inundated area is completely saturated. However, in several modelling studies that regard the river-aquifer interactions, the vertical infiltration under ponded conditions is modelled as a saturated soil flow process. In order to find out whether the assumption of saturated conditions under an inundation area is suitable or not, the saturated time of the soil below an inundated area is determined. This is realised by evaluating an analytical infiltration model with two example soils under different initial conditions and for different ponding depths. The model results show, that saturation of several meters of sandy soil under ponded conditions takes place within a period of hours. For the clay example, the saturation process happens within the order of days, and if the clay is initially dry, it can take even weeks. This leads to the conclusion that saturated model approaches are suitable for sand and gravel aquifers if they are not covered with a clay layer. While the ponding depth influences the infiltration rate and the progression of the saturation front in the sandy soil, for initially wet clay the infiltration rates were found to change only marginally with the ponding depth. [ABSTRACT FROM AUTHOR]