HR: 0800h
AN: H21B-1007    [Abstracts]
TI: Response of a shallow sandy unconfined aquifer to tidal loading from a low-relief estuary
AU: * Enot, P
EM: patricia.enot@ed.ac.uk
AF: Contaminated Land Assessment and Remediation Research Centre, Institute for Infrastructure and Environment, School of Engineering and Electronics, King's Buildings, The University of Edinburgh, Edinburgh, EH9 3JL United Kingdom
AU: Mao, X
EM: x.mao@ed.ac.uk
AF: Contaminated Land Assessment and Remediation Research Centre, Institute for Infrastructure and Environment, School of Engineering and Electronics, King's Buildings, The University of Edinburgh, Edinburgh, EH9 3JL United Kingdom
AU: Barry, D A
EM: d.a.barry@ed.ac.uk
AF: Contaminated Land Assessment and Remediation Research Centre, Institute for Infrastructure and Environment, School of Engineering and Electronics, King's Buildings, The University of Edinburgh, Edinburgh, EH9 3JL United Kingdom
AU: Li, L
EM: l.Li@uq.edu.au
AF: Environmental Engineering Division, School of Engineering, The University of Queensland, St Lucia, QLD 4072 Australia
AU: Binley, A
EM: a.binley@lanc.ac.uk
AF: Department of Environmental Science, Institute of Environmental and Natural Sciences, Lancaster, LA14YQ United Kingdom
AB: A field study of the physical and chemical processes occurring in a sandy, unconfined aquifer (Scotland, UK), connected to a low-relief estuary was performed, with an emphasis on groundwater salinization and water table fluctuations. Data were collected from two adjacent monitoring transects located 20 m apart. These extended from the line of zero flux inland towards the estuary. Drill logs show that geological variations between the two monitoring transects are negligible. One transect consisted of three Multi-Level Sampling (MLS) boreholes, allowing detailed depth-specific pore water collection. Water level measurements were derived from pressure transducers located in fully slotted boreholes in the second transect. Water table elevations, pore water Electrical Conductivity (EC) and salinity data, concentrations of halogen ions Cl and Br as well as exchangeable cations Mg, Ca, K and Na were collected during 2001-4 along the monitoring transects. The aquifer response induced by high-low and neap-spring tidal estuarine oscillations was measured. Water level data indicate groundwater fluctuations are influenced by tidal loading from the estuary. Spectral analyses of ground and estuary water level time-series indicate the dominance of the principal lunar semi-diurnal frequency. For all frequencies, damping increases rapidly inland; phase shifts are also observed. The influence of the site settings (especially beach slope) on the tidal signal propagation is discussed. Pore water chemistry indicates a limited salinization zone at depth in the aquifer, and Br/Cl ratio calculations confirm its marine origin. Variations in EC and Cl concentrations do not follow any tidal pattern even near the shore, but are more likely influenced by seasonally varying groundwater recharge. Exchangeable cation concentrations in the aquifer salinization zone show no significant changes over time , except very near to the estuary. Here, the link between observed groundwater chemistry variations and tidal forcing is established by cross-analysis of physical and chemical data. This saline zone where exchange processes are influenced by tidal loading, has been identified as the landward front of the active estuarine intrusion in the aquifer.
DE: 1806 Chemistry of fresh water
DE: 1829 Groundwater hydrology
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting