Suspended sediment and 137Cs fluxes during the exceptional December 2003 flood in the Rhone River, southeast France.

Titre de la revue : Geomorphology
Volume : 95
N° : 3-4
Pagination : 350-360
Date de publication : 15/03/2008

At the beginning of December 2003, one of the biggest floods for at least 150 years was recorded on the Rhone River. In the lower part of the river, the peak flood reached 11 000 m³ s-1. The geomorphological and radioecological consequences of such an event were investigated downstream all the nuclear installations by using measured and calculated fluxes and the total export of suspended sediment and associated 137Cs. Results pointed out the major role played by large floods in the annual suspended sediment load, as 3.70×106 tons of silts, 0.85×106 tons of sands and 0.84×106 tons of clays were transferred towards the coastal environment. Nevertheless, these solid loads were found to be lower than those expected as regards the liquid discharge reached during this event and suggested that previous floods which occurred on the river and on its main tributaries during the last decade have probably led to the removal of available sediment from the channels and their banks. Besides, the 137Cs activity measured within the suspended load was estimated at 14.9  0.4 Bq kg-1, which is a level characteristic of the suspended sediments from the Rhone catchment area and demonstrated that nuclear installations located along the Rhone valley do not significantly contribute to any increase in 137Cs activity in the water during the flood. The total 137Cs particulate export amounted to 77  17 GBq and was mainly associated with the silt fraction which contributes to around 70% of the total 137Cs export.