Rainfall is one of the major triggering factors of landslides, and its pattern controls their temporal behaviour. Characterization of the groundwater processes and possible preferential infiltration of rainfall is necessary, challenging and very relevant for landslide hazard analysis. The objective of this paper is to identify the groundwater dynamics (matrix flow and preferential flow) within highly heterogeneous and fissured reworked black marl material, using a large-scale infiltration test. The artificial rainfall experiment over a 100 m2 infiltration plot monitored with several hydrological, hydrochemical and geophysical equipments was carried out on the Super-Sauze mudslide (South French Alps). High resolution groundwater and water quality measurements were collected. Artificial rainfall was applied over a period of 14 days. Conservative tracers (Br− and Cl−) were used successively during the infiltration period. The mean rainfall intensity was 8·5 mm h−1 with a mean tracer concentration of 100 mg l−1. The hydrodynamic and hydrochemical responses of the tracing experiments allowed us to get a new insight into: (1) the horizontal and vertical variability of the rain infiltration in unstable black marl hillslopes; (2) the effect of shallow fissuration on the groundwater recharge; (3) the role of piston flow on the rate of water level changes and the increase of pore water pressures and (4) the effect of material heterogeneity in the development of preferential water flows and local perched water tables. Copyright © 2011 John Wiley & Sons, Ltd.