Considering the sedimentary diagenesis in models of radionuclides transfers in rivers
Titre du congrès :ASLO Summer Meeting
Ville du congrès :Saint-Jacques-de-Compostelle
Date du congrès :19/06/2005
When radioactive effluents are released into water, the pollutant is dispersed by the turbulent flow and it is distributed between a dissolved phase and a phase fixed on the suspended matter and the bottom sediment. Transfer between these two phases depends on flows of solid matter resulting from the sedimentary dynamics within the river. Particularly, the processes of deposition and erosion condition the formation of stocks of matter (and their associated pollutants) in some places of the river. These processes depend on both flow conditions and sedimentary diagenesis, i.e., on the degree of cohesion of the sediments which increases with the quantity and the age of the settled matter.
The subject of this work concerns the resuspension processes of the pollutant confined in the bottom sediment of rivers. It deals with the middle- and long-term becomings of the stocks. Which quantity of matter (and thus of pollutants) can be resuspended towards the water column, and under which conditions ?
The bibliographical study established that the deposition of suspended matter is accompanied by a structural rearrangement of the first layer of sediment (mechanical compressing), and then that a cementing process is relaying for the deeper layers (chemical consolidation). These elements will be used to set a first compression model which will consider the flow of deposition, conditioned by the flow conditions and the nature of the suspended matter. As an output, it will provide the exchange flow between interstitial water and the water column and a mechanical characterization of the main sedimentary layers. This sedimentary model will be coupled with a hydraulic model and a model of radionuclide transfers in rivers.
Within the framework of an application to the Rhone river, the parameterisation of this model will be carried out in laboratory, using cores of sediment sampled in-situ. These characterizations will rely on physicochemical analyses (oedometric profiles, granulometry, organic and mineral matter) and on the use of the flume HERODE (Hydraulic for EROsion and DEposit), built at the "Institut de Recherche sur les Phénomènes Hors Équilibre" (IRPHE, Marseille) in 2003 to study the erosion parameters associated with these cores. The qualification of the flume is reported on a companion poster