Flood series data for the later Holocene: Available approaches, potential and limitations from UK alluvial sediments

Abstract

Flood sediments characterise the alluvial record, though the series of floods these deposits record is a complex one because of variable deposition in different alluvial subenvironments. To date, flood sequences in the UK have been analysed using upland boulder berms, vertically accreting fills in contracting channels, cutoff fills and flood basin deposits. These cover different timespans ranging from c. 100—300 yr (berms and channel fills) to a limited set of the most extreme of Holocene events. Collation of future site data may allow record splicing to generate longer or more continuous series. Other sequences are potentially available from alternative depositional environments, including lateral accretion deposits, slackwater sediments in bedrock channels and palaeochannels. However, these have not produced UK results as yet, and there are reasons for them being less useful in this environment than has proved to be the case elsewhere. Finally, a new approach to overbank sedimentation sequences is presented. Analysing such deposits in much greater detail than hitherto gives flood series on a millennial timescale, and it is suggested that the prevalence of such sediments on UK floodplains may allow longer and more complete flood series data to be obtained than has otherwise been possible.