Hydrological characteristics of slope deposits in high tropical mountains (Cordillera Real, Bolivia)

The hydrological processes within slope deposits are not well known, particularly for high tropical mountains with climatic conditions giving seasonal contrasts in the hydrological cycle. Measurements have been taken in a high Andean valley of the Cordillera Real (Bolivia) with the aim to determine the role of the slope deposits in the framework of a hydraulic modelling. Different transfer time measurements combined with morphometrical and sedimentological analysis were carried out on three talus slopes and two moraines during the rainy season. After injection of salt, the electrical conductivity of the water in slope deposits springs is monitored to estimate transfer velocities. The hydrological behaviour of these slope deposits depends on the season. In the dry season, all the water infiltrates and there is no visible outlet. During the wet season, one part soaks in and gives springs down slope. The lag times estimated by the measurement of tracer velocity demonstrate that these slope deposits delayed the flow depending on the type of deposit. The delay is at least 24 h in the case of the talus slopes and more than 48 h in the case of lateral moraines.