The dynamics of 60Co- labelled sediment particles in the Seine estuary

From 1990 to 2000, 60Co, a radionuclide released into the English Channel by the La Hague reprocessing plant, has been measured in the deposited sediments of the Seine estuary. Since 1990, the 60Co concentrations have slowly increased from some tenths of Bq.kg-1to ca 10 Bq.kg-1. This transient signal was used to bring the evidence of the input of marine particles far upstream in the estuary, ca 80 km from the river mouth. The dynamics of this process have been deciphered by comparing several sets of data obtained in the years 1990 to 2000. An average velocity of about 10 km.y-1was found for this incoming sediment pool. These observations are conformable with calculated of suspended sediment fluxes performed along the river.