Late quaternary, palaeohydrology, palaeoecology and floodplain development of the lower river Severn
PublisherUniversity of Southampton
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Three principal approaches have been taken to the investigation of the Late Quaternary palaeohydrology of the Lower Severn: firstly historical hydrological analysis. secondly the analysis of floodplain sediments and palaeochannels, and thirdly palaeoecological analysis in order to reconstruct floodplain character and catchment conditions. Specific techniques used have included:- the interpretation of stratigraphic data. 14C dating. pollen and diatom analysis, and the multivariate analysisofgrain size profiles. During the Late-glacial and early Holocene the channel was of a bed load type carrying high and very variable discharges. but from the late Boreal onwards the channel was of a mixed - to suspended - load type and carried discharges similar to those of today. In historical times changes in mean discharge do not seem to have been as important as a decrease in flow variability. The principal palaeohydrological event of the Holocene was a dramatic increase In suspended sediment production during the early Iron Age. The floodplain underwent rapid vertical accretion often burying a peaty floodplain surface. Palaeoecological analyses of both floodplain and terrace depression sediments have shown that this accretion pcs t -da ted the deforestation of the lowland and terrace lime woods and was associated with arable agriculture. Both historical studies and floodplain stratigraphy consistently suggest late Holocene channel planform stability, and it is possible that this is due to rapid over bank accretion and natural levee construction, causing relative channel incision and preventing lateral migration. Within the last 1000 years man has reinforced channel stability and been responsible for decreased floodplain accretion.