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Keywords:

  • lowland permeable catchments;
  • channel bed sediment storage;
  • sediment budget

Abstract

Lowland permeable catchments in the UK are particularly prone to sedimentation problems, on account of the increased fine sediment loadings generated by recent land-use change and their stable seasonal hydrological regimes, which are frequently depleted by groundwater abstraction. Fine-grained sediment storage on the bed of the main channel systems of the Frome (437 km2) and Piddle (183 km2) catchments, Dorset, UK, has been examined at 29 sites using a sediment remobilization technique. Measurements encompassed the period February 2003–July 2004. At individual sites in the Frome, average values ranged between 410 and 2630 g m−2, with an overall mean of 918 g m−2. In the Piddle, the average values for individual sites varied between 260 and 4340 g m−2, with an overall mean of 1580 g m−2. Temporal variations in fine bed sediment storage at each site were appreciable, with the coefficients of variation ranging between 43 and 155% in the Frome and between 33 and 160% in the Piddle. Average reach-scale specific bed sediment storage increased markedly downstream along each main stem from 2 to 29 t km−1 (Frome) and from 4 to 19 t km−1 (Piddle). Total fine sediment storage on the channel bed of the Frome varied between 479 t (5 t km−1) and 1694 t (17 t km−1), with a mean of 795 t (7 t km−1), compared with between 371 t (5 t km−1) and 1238 t (14 t km−1) with a mean of 730 t (9 t km−1) in the Piddle. During the study period, fine bed sediment storage was typically equivalent to 18% (Frome) and 57% (Piddle) of the mean annual suspended sediment flux at the study catchment outlets. Copyright © 2006 John Wiley & Sons, Ltd.