Groundwater from the (largely unconfined) Chalk aquifer constitutes a major water resource. The unsaturated zone plays a crucial role in the hydrological cycle, determining the timing and magnitude of recharge, and the transport and fate of nutrients. However, despite over 30 years of study our understanding of this system is incomplete. The objectives of this research were to investigate the aquifer characteristics of the Chalk and to clarify the physical processes controlling the movement of water in the unsaturated zone. Combining results from laboratory tests, geophysical logs, CCTV surveys and field instrumentation comprehensive insights into unsaturated zone processes are provided. Stratigraphical and geographical distributions of aquifer properties were investigated and marl horizons shown to provide the principal contrasts in hydraulic conductivity. Results from novel testing procedures allowed the Chalk soil moisture characteristic to be quantified and suggested surface storage and film flow to be significant unsaturated zone processes. CCTV and geophysical surveys provided supporting evidence of this and also highlighted the role of marl horizons in controlling saturated and unsaturated flow. Geophysical surveys also showed that the Chalk lithostratigraphy can be related to physical characteristics and fracturing which act to control recharge processes. Recharge was studied at two instrumented sites allowing matric potential to be monitored beyond depths previously attempted. At East IIsley, Berkshire, UK, recharge occurred throughout the year via the matrix, contrastingly, at North Heath Barn, Sussex, UK, the capacity for vertical drainage was low and evidence suggested that episodic lateral fracture flow would occur instead of vertical recharge. The instrumentation also showed that the water level in an unlined observation borehole can be influenced by processes in the unsaturated zone and may be an unreliable indicator of the water table. The findings of this study have important implications for the representation of recharge in groundwater models and the reliability of the parameterisation and predictions of these models. The presence of stratigraphically constrained recharge pathways suggests focused recharge to be a significant, although poorly understood, process controlling recharge to the Chalk.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:589950 |
| Date | January 2012 |
| Creators | Molyneux, Ian |
| Publisher | University of Brighton |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | https://research.brighton.ac.uk/en/studentTheses/b26168fa-c6bf-4bf4-851c-15a91d455525 |
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