Use of fallout 137Cs in investigations of overbank sediment deposition on river floodplains

River floodplains have been recognised as important sinks for storing suspended sediment and associated contaminants mobilised from the upstream catchment. However, information on contemporary rates of overbank sedimentation is difficult to obtain using conventional methods. Measurements of the 137Cs content of floodplain sediments provide an alternative approach to obtaining; estimates of medium-term rates (ca. 40 years) of overbank sediment deposition. The 137Cs approach requires only a single site visit and minimum sample preparation. Furthermore, it is capable of providing information on spatial patterns of sediment deposition on floodplains, which is needed to improve our understanding of the processes involved in overbank flow and sediment deposition. This paper reviews the basis for using 137Cs measurements in floodplain sedimentation studies and presents improved procedures for interpreting 137Cs profiles in floodplain sediments and for obtaining estimates of sedimentation rates from single measurements of the total. 137Cs inventories of bulk sediment cores. The results obtained from a case study undertaken on the floodplain of the River Stour, Dorset, UK, are presented.