Trapping and Tracing: Some Recent Observations of Supply and Transport of Coarse Sediment from Upland Wales

  1. J. D. Collinson and
  2. J. Lewin
  1. B. Arkell1,
  2. G. Leeks2,
  3. M. Newson2 and
  4. F. Oldfield1

Published Online: 29 APR 2009

DOI: 10.1002/9781444303773.ch8

Modern and Ancient Fluvial Systems

Modern and Ancient Fluvial Systems

How to Cite

Arkell, B., Leeks, G., Newson, M. and Oldfield, F. (2009) Trapping and Tracing: Some Recent Observations of Supply and Transport of Coarse Sediment from Upland Wales, in Modern and Ancient Fluvial Systems (eds J. D. Collinson and J. Lewin), Blackwell Publishing Ltd., Oxford, UK. doi: 10.1002/9781444303773.ch8

Author Information

  1. 1

    Department of Geography, University of Liverpool, Liverpool L69 3BX, UK

  2. 2

    Institute of Hydrology, Staylittle, Llanbrynmair, Powys, Wales, UK

Publication History

  1. Published Online: 29 APR 2009
  2. Published Print: 7 FEB 1983

ISBN Information

Print ISBN: 9780632009978

Online ISBN: 9781444303773

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Keywords:

  • trapping and tracing - supply and transport of coarse sediment from upland Wales;
  • drainage ditching and sediment yields;
  • magnetic tracing;
  • tracer methodology;
  • magnetic tracing within ditch systems;
  • downstream tracing with magnetic technique

Summary

The work reported is part of a project to investigate the relationship between upland land-use, sediment yield and river engineering problems in mid-Wales. Observations of bedload trapping in the forested uplands showed that the erosion of open drainage systems has increased yields; periods of supply-limited and transport-limited yield have been identified.

This paper describes the application of a new magnetic tracing technique to the study of sediment movement in the uplands, from the uplands into the piedmont zone, and from shoal to shoal in that zone. The technique, based on the enhancement of the magnetic susceptibility of the natural bedload provides an effective tracer material which can be detected in low concentrations, and in all particle size ranges. Special field and laboratory techniques associated with the method are described.

In rapidly eroding forest drainage ditches, tracing with particular size ranges from small shoals to bedload traps is improving both the theoretical and technical aspects of the technique. In these source areas, tracer recovery rates of 63% are demonstrated. Downstream from such source areas, the use of the natural bedload in tracing allows replication or replacement of local structure; armour or paving layers can be reproduced. Preliminary observations of the complexities of bed sediment movement at sites on the Rivers Wye, Severn and Llwyd are described.