Reconstructing Historical and Holocene Flooding in Welsh River Catchments

Project Staff

Principle Investigator

Dr Anna Jones

Co-Investigators

Professor Mark G. Macklin
Dr Paul Brewer

Brief Description

From PhD thesis (2007):

Abstract

In Wales, river flow gauge records rarely exceed 45 years in length and in sparsely populated rural Welsh catchments documentary flood records tend to be patchy prior to c. AD 1900. These records are rarely of sufficient length, and sometimes quality, to produce accurate estimates of present and future flood hazard in river catchments, particularly for low-frequency high-magnitude flood events. This study combines traditional geomorphological methods, including geomorphological mapping, sediment coring and radiocarbon dating, with novel analytical techniques, such as high-resolution XRF core scanning, and analysis of instrumental flow data to reconstruct records of historical and Holocene flooding in four Welsh river catchments: the upper Severn, Dee, Teifi and Dyfi.

Analysis of flow gauge data indicates that clustering of relatively high-magnitude flood events has occurred since the 1960s, although the timing of these clusters varies between the four catchments. High-resolution XRF analysis of five palaeochannel sediment cores from two contrasting reaches within the upper Severn catchment, coupled with the use of lithogenic element ratios Zr/Rb and Zr/Ti as grain size proxies, has been used to produce high-resolution records of flooding for the historical period. These analyses indicate that there have been six episodes of increased flood occurrence during the past c. 1000 years, including two during the period since AD 1845.

Seven episodes of increased flood occurrence since c. 7000 cal BP have been identified using the dates of fluvial discontinuities, and the estimated ages of major flood events, in the study catchments and in previous studies of valley floor development in Wales. These episodes of increased flooding in Welsh catchments coincide with episodes of significant flooding in the British Holocene alluvial record and with increases in mire surface wetness in northern Britain since c. 4400 cal BP.