HR: 0800h
AN: H41C-0314    [Abstracts]
TI: Tidal Influence on Behaviour of a Coastal Aquifer Adjacent to a Low-Relief Estuary
AU: * Mao, X
EM: xmao@ed.ac.uk
AF: Contaminated Land Assessment and Remediation Research Centre, Institute for Infrastructure and Environment, School of Engineering and Electronics, The University of Edinburgh, Kings Buildings, United Kingdom, Edinburgh, EH9 3JL United Kingdom
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, The University of Edinburgh, Kings Buildings, United Kingdom, 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, The University of Edinburgh, Kings Buildings, United Kingdom, Edinburgh, EH9 3JL United Kingdom
AU: Li, L
EM: l.li@uq.edu.au
AF: Centre for Eco-Environmental Modelling, Hohai University, Jiangsu, Nanjing, 210098 China
AU: Li, L
EM: l.li@uq.edu.au
AF: Environmental Engineering Division, School of Engineering, The University of Queensland, St. Lucia , Queensland, Brisbane, QLD 4072 Australia
AU: Binley, A
AF: Department of Environmental Science, Institute of Environmental and Natural Sciences, University of Lancaster , England, Lancaster, LA1 4YQ United Kingdom
AB: Tide-induced groundwater flow will influence the degree of salt-water intrusion and contaminant transport in an unconfined coastal aquifer. However, the magnitude of such influence is uncertain, especially for a mildly sloping beach. Here a costal aquifer adjacent to a low-relief estuary at Ardeer (Scotland) is investigated both with field monitoring and numerical modelling, in order to ascertain the tidal influence on the groundwater dynamics, salt water intrusion, and chemical migration to the estuary. A field survey and aquifer monitoring were carried out to acquire data on the aquifer geology, water table fluctuations and salinity distributions. The observed groundwater fluctuations were asymmetric and skewed in time. Analysis revealed that the semi-diurnal fluctuations were not efficiently filtered out in the area near the beach, although their magnitude decreased greatly further inland. The measured salinity distributions indicated that salt-water intrusion occurred both in the bottom part of the estuary and near the beach surface. A numerical model (SEAWAT) was used to simulate flow processes in the cross-section perpendicular to the estuary. Results show that the simulated groundwater table fluctuation was in good agreement with the collected data. The case with a vertical beach (an extreme condition opposite to a low-relief beach) was also simulated for the purpose of comparison. It was found that tidal fluctuations affected significantly the hydrodynamics in the aquifer. Especially for the mildly sloping beach, a circulation cell was formed below the beach when the groundwater was retreating to the estuary, a feature that did not appear in the vertical beach case. Within the aquifer, the asymmetry in water table fluctuations was captured by the simulation with the mildly sloping beach, but was less obvious in the vertical beach simulation. Comparison of the predicted salinity distributions in the aquifers shows that the mild beach slope enhanced salt water intrusion. This occurred in two ways (at the mildly sloping beach): first, the salt water wedge in the lower part of the aquifer advanced further into the inland area and secondly, the infiltrated salt water induced a large mixing zone just under the sloping beach. Contaminant transport from the aquifer to the estuary was also affected. The mildly sloping beach tended to reduce the horizontal advection of the plume towards the estuary but accelerated the upward contaminant migration towards the beach surface, which potentially puts estuarine ecology at risk with beach pollution.
DE: 1800 HYDROLOGY
DE: 1824 Geomorphology (1625)
DE: 1829 Groundwater hydrology
DE: 1832 Groundwater transport
SC: Hydrology [H]
MN: 2004 AGU Fall Meeting