Chalk regional groundwater models and their applicability to site scale processes

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Title: Chalk regional groundwater models and their applicability to site scale processes
Authors: Parker, Simon John
Item Type: Thesis or dissertation
Abstract: Chalk is an important aquifer in England. Because of the highly permeable nature of the subsurface, groundwater moves relatively quickly, so that source area for a Chalk stream can change significantly on a seasonal basis. This research looks at both the hydrogeology at site scale and regional scale ground- water models in the Berkshire downs. At the regional scale, two conceptualizations of aquifer transmissivity, a zone-based approach and an interpolated transmissivity field approach, were implemented in the regional groundwater model with multiple parameterizations for each approach. For the river Lambourn, one river within the regional system, model output from both conceptualizations was then used to construct time series of groundwater catchment area based on the piezometric surface. It was found that the ground- water catchment area was highly variable, with values for maximum areas almost double those for minimum areas. Delineation of the groundwater catchment using field data also demonstrated that the area was highly variable. The comparison of model-derived area and field-data derived area resulted in the elimination of some model configurations unable to be eliminated based on groundwater heads and streamflows alone. The variability in the catchment area also challenges the use of a fixed area that is implemented in conceptual models of these catchments. At site scale, an initial approach to make inferences about flow directions in streambed sediments based on piezometric head data was abandoned because the high permeability of such sediments prevents the detection of head differences. Instead, high frequency logging of water temperature and water electrical conductivity were used to build an understanding of the hydrogeology at site scale. Both variables were found to be excellent tracers. It was found, however, that they are best used in conjunction with one another and that high frequency logging is important, as flowpaths can rapidly switch on and off.
Content Version: Open access
Date Awarded: 2011
Copyright Statement: Creative Commons Attribution NonCommercial NoDerivatives Licence
Supervisor: Butler, Adrian
Wheater, Howard
Sponsor/Funder: Natural Environment Research Council
Department: Civil and Environmental Engineering
Publisher: Imperial College London
Qualification Level: Doctoral
Qualification Name: Doctor of Philosophy (PhD)
Author Permission: Not granted
Appears in Collections:Civil and Environmental Engineering PhD theses

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