Programme OS1n Water quality 2
Impact of the hydrologic behavior on the pollutant dynamics in an
intermittent Mediterranean river (Vène, France).
Author(s): Marie-George Tournoud, Jean-Louis Perrin, Christian
Salles, Audrey Caro, Bernadette Picot, Claire Rodier, Christine Grillot, Chu Yin
Montpellier 2 (UM2), HydroSciences Montpellier (UMR CNRS-IRD-UM1-UM2), F-34095 Montpellier Cedex
Tel : +33(0)4 67 14 42 72
Fax : +33(0)4 67 14 47 74
Email : marie-george.tournoud@univ-
Keyword(s): intermittent river, hydrological behaviour, pollutant dynamics, pollutant fluxes
Session: OS1n Water quality 2
Intermittent Mediterranean rivers show long draught periods interrupted by floods of high
intensity and short duration. Their channel network structure is also highly variable in space and time. Water quality
dynamics in these rivers is highly impacted by this specific hydrological behaviour.
During the dry period, the river
channel may dry up completely except in some reaches where anthropogenic point-source inputs (mainly waste
water treatment plant effluents) contribute to maintain some pools. Accumulation of pollutants is observed in these
reaches. During the first floods, flow is rarely continuous throughout the channel network, because of the existence of
transmission losses. At the start of a storm, the advance of flood waves is limited by channel infiltration but also by
localized storage in small pools. Total flood volumes therefore do not increase very much and even decreases
downstream. Some floods observed in the upstream part of the river are not transferred to the outlet. This, in turn,
influences the spatial and temporal dynamics of pollutant fluxes. Along the river course, pollutograph shapes show
significant differences. Intense autumn floods flush away suddenly the pollutants from the soils and the river bed, but
significant quantity of pollutants may remain trapped in the riverbed, if transmission losses are too high.
the hydrological regimes of intermittent Mediterranean rivers are known, more knowledge is needed about the
processes governing pollutant transport as well as the ranking of the origins of the pollutants. Thus, it is necessary to
set up a special observation network in order to determine the temporal and spatial variability of the water and
pollutant contributions to the river.
All these phenomena will be illustrated on the case of the Vène River (67 km²,
South of France) over the observation period : from September 2003 to August 2006, on suspended solids,
nutrients and faecal bacterias. The combination of continuous and event based monitoring coupled with the multi-
scale sampling strategy allows a global understanding of the factors and processes influencing water quality at the
catchment scale: concentration data is used to assess the contamination levels of the river and the bio-disponibility of
pollutants, while by analysing the instantaneous fluxes the various contributions to the river might be established.
Finally the total load is calculated in order to evaluate the exports at the catchment outlet. The multi-disciplinary
approach followed herein improved our knowledge of the integrated catchment response and its impact for