Ž . Geomorphology 24 1998 209–223 The spatial variability of overbank sedimentation on river floodplains D.E. Walling ) , Q. He Department of Geography, UniÕersity of Exeter, Exeter, EX4 4RJ, UK Received 25 May 1997; revised 7 November 1997; accepted 16 November 1997 Abstract River floodplains are important landforms, and information on rates and patterns of overbank sediment deposition is essential for understanding their development. Such information is also needed for validating existing overbank floodplain flow and sediment transport and deposition models. The use of bomb-derived 137 Cs for documenting rates of overbank sediment deposition on river floodplains offers the potential for assembling data for a large number of points on a floodplain and therefore for investigating the spatial patterns involved. This approach also overcomes some of the operational and sampling problems encountered in traditional monitoring techniques. The study reported uses 137 Cs measurements on sediment cores to investigate the spatial variability of sediment deposition on selected floodplain reaches of five British lowland rivers. Attention is given both to the overall reach and to more detailed investigations of small areas. The observed spatial patterns of sediment deposition are interpreted in terms of the major controls involved, which include the floodplain microtopography and morphology. The relationship between the grain size composition of deposited sediment and sedimentation rate is also considered. q 1998 Elsevier Science B.V. All rights reserved. Keywords: Cs-137; floodplains; overbank deposition; sedimentation rate; spatial variability 1. Introduction River floodplains have attracted increasing atten- Ž . tion in recent years cf. Anderson et al., 1996 . This interest reflects, at least in part, the ecological signif- icance of floodplains and river corridors within the landscape, their importance as a buffer between the river and the surrounding land, and their role in providing storage for flood control. There is also a growing awareness of their potential significance as sinks for river-borne sediment and associated nutri- ) Corresponding author. ents and contaminants. Because of their dynamic nature, sediment deposited on river floodplains may be reworked in the future and may thus also consti- Ž tute a problem for future river management cf. . Leenaers and Schouten, 1989 . Against this back- ground, there is clearly a need for an improved understanding of the geomorphological evolution of floodplains and their role as sediment sinks. When considering the evolution of floodplains and their role as sediment sinks, attention commonly focuses either on the coarse channel deposits and the interaction between channel migration and floodplain Ž construction and destruction cf. Wolman and 0169-555Xr98r$19.00 q 1998 Elsevier Science B.V. All rights reserved. Ž . PII S0169-555X 98 00017-8