Sedimentary and geochemical balances in the Wettingen reservoir, Switzerland
The dam of Wettingen, located on the Limmat River downstream of the city of Zürich, is a run-of-river dam without sediment flushing. Its sedimentation history since its construction in 1932, has been established by transverse depth profiles periodically monitored on behalf of the Confederation. A regular sampling of the suspended matter and the sediments of the major tributaries (rivers and sewage treatement plant) during one year, as well as the entry and the outlet of the reservoir have enable to establish the sedimentary and geochemical balances. Suspende matter has been analyzed for two classes of organic micropollutants (PCBS, PAHS). The particle size distribution, organic matter and analysis of 12 metals have been carried out on all samples.
Today, 45% of the reservoir volume is filled in with sediments, including a layer dating from the 1950's to about 1975. This layer is severely contaminated by heavy metals and organic micropollutants. The current sediment loads are characterised by a deposition rate of 50% in the reservoir during average discharge periods, but reaching 90% during floods. The reservoir sedimentation is very strongly related to the history of floods. The contribution of the various tributaries represents only one percent of the total contaminant inputs and becomes almost insignificant in a period of flooding of the Limmat River. The main contribution of pollutants originates from upstream of the reservoir, probably in the city of Zurich. The presence of contaminated sediments raises the problem of the remobilization of pollutants by leaching, by plants and other living organisms, or even by erosion.
Framework/Financing : l'EWZ (Elektrizitätswerk der Stadt Zurich) and the University of Geneva.
Supervisor and colleagues directly involved :
Supervisor of thesis : Walter Wildi.
Collaboratrice involved: Stéphanie JUSTRICH, PhD candidate