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Hydrodynamics of floodplain wetlands in a chalk catchment: the River Lambourn, UK

Grapes, T.R. and Bradley, C. and Petts, Geoffrey E. (2006) Hydrodynamics of floodplain wetlands in a chalk catchment: the River Lambourn, UK. Journal of Hydrology, 320 (3-4). pp. 324-341. ISSN 0022-1694

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Official URL: http://dx.doi.org/10.1016/j.jhydrol.2005.07.028

Abstract

Variations in floodplain channel water levels and valley floor groundwater levels (measured in piezometers and boreholes) are examined at selected points along the course of the River Lambourn, a chalk river in southern England. A local alluvial gravel aquifer in the valley bottom is associated with numerous small wetlands that extend over much of the river's perennial profile. Variations in hydraulic gradient between local borehole levels and/or floodplain channel water levels are described for three sites in the seasonal section of the channel at Bockhampton, East Garston and West Shefford. The results indicate that observed groundwater levels are closely associated with flows from discrete springs at the margins of the channel and floodplain. However, as the floodplain widens and the alluvial gravel aquifer increases in size, the gravel aquifer accounts for a substantial down-valley component of groundwater flow with a diffuse vertical water flux. In the lower catchment, the exchange of flows between the gravel aquifer and the river enables some attenuation of floodplain water-table variability, providing a stable hydrological regime for valley-bottom wetlands. Catchment controls upon the local, valley-bottom, wetland regime are demonstrated with the application of a simple groundwater model developed using MODFLOW. The model is used to simulate groundwater discharge to the river in the upper and lower catchment, in addition to the water level regime at selected points in the valley bottom in the lower catchment. The results demonstrate the importance of taking catchment-scale water flow into account when managing isolated wetlands in a permeable catchment.

Item Type:Article
Research Community:University of Westminster > Life Sciences, School of
ID Code:9121
Deposited On:16 Feb 2011 14:40
Last Modified:16 Feb 2011 14:40

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