On the soil erosión in ravines of Antofagasta and its influence on the onset of a mudflow event

Abstract

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.