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Title: Fine sediment deposition in the River Keer : geomorphological assessment
Author: Jim Walker
Document Type: Monograph
Morphologically the Keer is a typical example of an "upland" gravel bed river. Its headwaters and upper reaches (source to approx. 4 km. downstream) exhibit comparatively low sinuosity and high gradient, giving high velocities, erosive power and sediment transport capabilities. Consequently bank erosion is common, but the bed surface comprises coarse gravel and cobbles and finer material is transmitted downstream. In the case of the Keer two factors serve to polarise these characteristics, the drift geology and soil associations of the catchment largely comprise of recent Alluvial drift and Wick 1 brown earths, such materials are well-drained sands and gravels and sandy-loams, which give rise to relatively erodible river banks. Secondly catchment rainfall is high, and the river regime is flashy, fast rise times and high discharges serve to further increase erosive impact and sediment transport efficiency. Further downstream, (including the remainder of the study reach), channel gradient is reduced, average channel width increases slightly with increasing flows, and the sinuosity of the river increases. This affects a natural reduction in velocity, erosive power and sediment carrying capacity. Under natural conditions erosion will still occur, particularly under high flow conditions, but it is generally localised to the outside banks of meanders. Deposition will also occur locally, and with bedforms such as point, side and occasionally medial bars forming frequent features of the bed environment. However erosion occurs predominately under high flows, and thus sediment supply and sediment transport capacities retain a state of fluctuating equilibrium. Therefore, although some fine sediment may exist, particularly in depository features such as bars, the bed surface generally comprises of fine and medium gravels. Most fine sediment is transmitted fairly rapidly to downstream estuarine environments, where it naturally accumulates, in an eco-system adapted to a high fine sediment yield.
Publisher: Environment Agency
Publication Date: 1997
Publication Place: Warrington
Subject Keywords: RiversSedimentsGeomorphologyWater qualitySedimentationWater erosionEnvironmental managementRiverbanksRiverbank protectionErosion control
Geographic Keywords: Keer (Lancashire)LancashireLune catchment
Extent: 11; + appendix
Total file downloads: 32

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