A critical zone observatory dedicated to suspended sediment transport:
the meso-scale Galabre catchment (southern French Alps)
Abstract
The 20 km² Galabre catchment belongs to the French network of critical
zone observatories. It is representative of the sedimentary geology and
meteorological forcing found in Mediterranean and mountainous areas. Due
to the presence of highly erodible and sloping badlands of various
lithologies, the site was instrumented in 2007 to understand the
dynamics of suspended sediments (SS) in such areas. Two meteorological
stations including measurements of air temperature, wind speed and
direction, air moisture, rainfall intensity, raindrop size and velocity
distribution are installed both in the upper and lower part of the
catchment. At the catchment outlet, a gauging station records the water
level, temperature and the turbidity (10 min. time-step). Water and
sediment samples are collected automatically to estimate SS
concentration-turbidity relationships, providing SS fluxes
quantifications with known uncertainties. The sediment samples are
further characterized by measuring their particle size distributions
(PSD) and by applying a low-cost sediment fingerprinting approach using
spectrocolorimetric tracers. Thus, the contributions of badlands on
different lithologies to total SS flux are quantified at a high temporal
resolution providing the opportunity to better analyze the links between
meteorological forcing variability and watershed hydrosedimentary
response. The set of measurements was extended to the dissolved phase in
2017. Both the river electrical conductivity and its major ion
concentrations are measured each week and every three hours during storm
events. This allows progress in understanding both the origin of the
water during the events and the partitioning between particulate and
dissolved fluxes in the critical zone.