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Coupled water and nutriment modelling of an intermittent French river: The Vène

IWRA World Water Congress 2008 Montpellier France
5. Water Governance and Water Security
Author(s): Nanée Chahinian
Marie-George Tournoud
Jean-Louis Perrin
Bernadette Picot
HydroSciences Montpellier UMR CNRS-IRD- UM1-UM2, Université Montpellier 2, Case courrier MSE, Place Eugène Bataillon, F-34095 Montpellier Cedex 5, France. Tel : +33(0)4 67 14 90 21 Fax : +33(0)4 67 14 47 74 Email : chahinian@msem.univ- montp2.fr

Keyword(s): Modelling, Hydrology, Water Quality, Nutrient

AbstractIntermittent rivers have a specific hydrological behaviour resulting in long draught periods interrupted by floods of high intensity and short duration which also influence the water quality dynamics. Indeed during low flow periods pollutants accumulate in the river bed and are flushed away by the first floods. The stream’s water quality will thus by governed by the interaction between the hydrological conditions of the river and its chemical and biological status. These rivers are widespread in semi-arid countries and the temporal and spatial variability of their flows induce great management problems. They are also difficult to model because sharp variations in flow and river bed wetness are still not correctly represented in most models. In addition, errors on flow simulation, especially during low flow periods, have direct repercussions on water quality simulations. However, there is a great demand for models as they are good tools to predict the impact of management changes on both the river and the downstream water bodies. The objective of this work is to model the hydrological and water quality dynamics of an intermittent river. The latest version of the Soil and Water Assessment Tool (SWAT 2005) is used to simulate phosphorous and nitrogen transport on the Vène experimental catchment for which data is available since 1994. The results indicate that the model is sensitive to the prediction errors on flows and to the partitioning between particulate and dissolved form for a given nutrient. The results also highlight the need for a better representation of the channel rewetting processes.
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