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Keywords:

  • hillslope hydrology;
  • artificial tracing;
  • sprinkling experiment;
  • infiltration;
  • French South Alps;
  • landslide

Abstract

Few studies exist on infiltration processes in badlands, although infiltration and subsurface lateral flows are known to contribute to soil erosion and to control slope instability. Our investigation was carried out in a 100-m² plot located in a 0.5-ha landslide in black marls (south-east France). An artificial sprinkling was performed with an intensity of 10 mm h−1 during 66.4 h interrupted with 8.4 h breaks. KBr and KCl were used as tracers.

A pseudo-steady state was reached after 25–35 h and 250–350 mm of rainfall. The runoff coefficient was 40% (ratio total runoff volume/total sprinkling water amount). Pre-event water (PE) contributed to the groundwater recharge at the very beginning of the experiment, but PE contribution dropped steadily while the soil was saturating. After around 200 mm of cumulative rainfall, PE contribution started to rise steeply before reaching a nearly constant value. This original mechanism implies an efficient transfer process of PE. It was assumed from the description of the material structure and from hydrological evidences that PE was mainly drained from a structure porosity made of marl's flaked nature. Total PE contributions ranged from 25% to 79% (PE contribution was over 50% in 2/3 of the observation wells). Over the recession phase, release of PE occurred from the drainage of texture porosity. The study showed that at the plot scale, infiltration processes proved to be well organized despite the high heterogeneity and anisotropy of the material. It was possible to propose a general conceptual model explaining the hydrological processes over time and area. The peculiar structure of regolith originating from black marl is preserved over a large part of the weathering time so that the material structure (type, orientation of grains, small/large pores) remains a first-order control of water flow generation in black marl soils. Copyright © 2012 John Wiley & Sons, Ltd.