The IERC is participating in a project to develop a computer simulation system of the Rhone Valley and the neighbouring coastal waters. The aim of this is to explore the possible impacts of economic and demographic development and of environmental policies on the water quality of the river and the coastal waters, as an input to socio-economic and environmental policies. The simulation links the changing pattern of human activities, settlement pattern and transportation links in the Rhone Valley to the many inputs, both dispersed and point sources, of organic matter, nitrates and phosphates to the different sub-basins of the river. These feed into a connected model of the different sub-basins, each one reflecting its own rainfall, evapotranspiration, slopes and soil types, so as to produce the flows of water, and the changing biological and chemical composition of the water in several stream levels and in the main branch of each sub-basin. The model consists of a coupled set of non-linear differentiql equations, which can be chosen to operate at different levels of spatial detail: a) as a single basin with a hierarchy of successive stream orders treated on average at each level, or b) as 11 connected sub-basins with each of these 11 treated as a hierarchy of stream orders, or c) as 221 connected sub-basins with each of these treated on average. The results have been compared with data and seem to generate water flows, nitrate and phosphate concentrations successfully. The results show clear "non-linear" effects such as existence of threcholds for the onset of eutrophication. The flows from the lower branches will be modelled as they flow into the Delta region and then out to sea. The output of the Rhone Valley will then be coupled to a 3-D ecological model of the Golfe du Lions, in order to estimate the possibility of eutrophication.
Using data concerning changing populations and jobs at the level of the 400 or so Cantons that make up the Rhone Valley, we have developed a dynamic framework to generate the geographical pattern of inputs to the river system, as a result of the past and possible future social and economic development and of environmental restrictions. The complex equations describing the microbiology, chemistry and physical processes in rivers were developed originally at the University of Brussels, and these have been adapted to the Rhone Valley system. The variables whose changing concentrations are described by dynamic equations include: nitrates, methane, dissolved and particulate phosphates and organic matter of different activity levels, oxygen, and ammonia as well as phytoplankton, zooplankton and bacteria. Processes of sedimentation and of reactions between the sediment levels and the water are taken into account according to the different flow rates and loads. The data concerning inputs to the Rhone, and the different decision makers and actors involved are being studied by a team at the Ecole Nationale des Ponts et Chausées, and the physical and ecological model of the coastal waters is being developed by the Institut de Biogéochimie Marine, of the Ecole Normale Supérieure, in Paris.
Issues that are important are not only those of direct environmental policy concerning pollution and discharge into the river, but also issues of agricultural growth or decline, since both over-exploitation and abandonment of land can lead to massive erosion and to changes in the geomorphology of the river basin, and to floods and disasters downstream.
Report in Preparation.
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Last Updated: 7th October 1996.