HR: 1340h
AN: H53F-1474    [Abstracts]
TI: Numerical study of the airflow in the unsaturated zone induced by sea tides
AU: * Guo, H
EM: hpguo@hkusua.hku.hk
AF: Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, (852), China
AU: Jiao, J J
EM: jjiao@hku.hk
AF: Department of Earth Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, (852), China
AB: Air pressure in coastal unsaturated zones fluctuates in response to tidal fluctuations, as does the ground water level in the aquifer. Air-water two-phase flow induced by sea tides in a coastal two-layered subsurface system is investigated through numerical simulations. The system consists of upper and lower layers with permeabilities of kU and kL, respectively. Water table exists in the lower layer. The tide-induced water level fluctuation may result in significant air pressure fluctuations above the water table in air-confined aquifers, i.e., the permeability of the upper layer is about two orders of magnitude lower than that of the lower layer. The air pressure fluctuations attenuate upward in the vertical direction, while the air pressure amplitudes tend to increase until reaching a maximum and then decrease in the horizontal direction. The simulation results show that the local hydraulic head, rather than the sea tide, is the direct driving force of the air pressure fluctuations in the unsaturated zones. When kU is reasonably great, the air pressure depends mainly on the changing rate of the local hydraulic head. When kU is low, however, the air pressure depends mainly on the amplitude of the local hydraulic head. The air flux fluctuations across the ground surface attenuate landward gradually. An interesting phenomenon is that the air flux amplitude tends to increase with kU at areas close to the coast, but to decrease with kU at areas far away from the coast.
DE: 1847 Modeling
DE: 1865 Soils (0486)
DE: 1875 Vadose zone
SC: Hydrology [H]
MN: 2007 Fall Meeting