4.7 Article

River entrenchment and terrace formation in the UK Holocene

Journal

QUATERNARY SCIENCE REVIEWS
Volume 76, Issue -, Pages 194-206

Publisher

PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.quascirev.2013.05.026

Keywords

River terraces; River incision; Holocene; Flood events; Environmental controls

Funding

  1. Welsh Assembly Government
  2. Higher Education Funding Council for Wales of the Centre for Catchment and Coastal Research at Aberystwyth University
  3. Natural Environment Research Council [NE/G019916/1] Funding Source: researchfish
  4. NERC [NE/G019916/1] Funding Source: UKRI

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A meta-analysis of a large database of C-14 dated fluvial units is used to assess the chronology and controls of episodic Holocene river entrenchment and terrace formation in the UK. Most Holocene terraces are of a 'fill-cut' type developed in Pleistocene sediments, in places now reaching down to pre-Holocene bedrock. Holocene terraces are widespread in higher-relief areas of the UK and peripheral higher-energy rivers, and include up to 7 levels in some valley floor reaches. Using C-14 constrained data subsets for incision episodes, the onset, vertical ranges, formation times, and rates of entrenchment are examined, together with geographical distributions. The height range of terrace separation is relatively small (0.5-3.5 m) with a long-term averaged incision rate over the late and mid-Holocene of 0.43, 0.5, 0.67, 0.7 and 0.81 m/ka in the Tweed, Rheidol, Severn, Ouse and Ribble catchments, and a regional similarity in the scale of incision events. The periods 4200-3700, 3100-2900, 2100-1900, 1800-1500 cal. BP and most notably the last 1000 years (with prominent peaks at 900-800 and 700-600 cal. BP) were times of accelerated incision. It appears likely that extreme flood events triggered the formation of incision 'slots', rather than entrenchment being a direct response to glacio-tectonic uplift, or the result of incremental valley-floor lowering by combined incision and lateral reworking. River entrenchment has also been rapid in recent centuries, reflecting the coupling of extreme-events with anthropogenic effects on catchment hydrology. Incision results in changes of river channel flood power and overbank flood extent, and improved data on the long-term and large-scale vertical tendency of UK rivers are needed for flood risk management purposes. (c) 2013 Elsevier Ltd. All rights reserved.

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