题目：Subsurface air flow induced by tidal fluctuation, rain infiltration and pumping tests
报告人：  郭海朋
Department of Earth Science, The University of Hong Kong
时间：11月19日（周三）下午3:00-4:00
地点：方正大厦301会议室

报告内容摘要：
Ubsurface airflow has received much attention in hydrogeology. This work is the result of an attempt to investigate natural or artificial airflow in subsurface systems and consists of three parts. The first part is a numerical study of two-phase air-water flow in unsaturated zones induced by the sea tides. Simulations were made to investigate how the tide-induced air pressure fluctuations in the unsaturated zone change with the permeability of the porous media, distance from the coastline and depth below the ground surface. It is well known that the air flux across the ground surface can be affected by the fluctuation of the atmospheric pressure. However, the tide-induced air flux across the ground surface has not been addressed in the literature. The net effect of the tidal fluctuation on the air flux across the atmosphere-soil interface is explored. A case study is described to investigate tide-driven groundwater and air flows in a beach aquifer system in Dongzhai Harbor, Hainan, China. Monitoring results of the air pressure in the atmosphere and the unsaturated zone as well as the water level in the saturated zone are presented, and the relation between the air pressure and the water level is analyzed. In the second part, a transient, three-dimensional and variably saturated flow model was employed to study the air and groundwater flows in the soil under rain conditions. The objectives of this part are two-fold: to evaluate the reliability of the theory of the Lisse effect presented by Weeks (2002) to predict its magnitude in modeled situations that mimic the physical complexity of real aquifers, and to conduct parametric studies on the sensitivity of the water-level rise in the well to soil properties and the rain event. The simulation also explores the sensitivity of the Lisse effect to the van Genuchten parameters and the water table depth. The third part presents a numerical study of two-phase air-water flow induced by pumping tests. We believe that large negative pressures can be generated in a two-layered system when the upper layer is much less permeable than the lower layer, thus sealing off air exchange through the ground surface. Through numerical studies, this hypothesis will be tested and the scenario which generates the most significant negative pressure will be identified. It is also expected that pumping-induced negative air pressure may influence water level changes and consequently parameter estimation due to interaction between airflow and water level. The impact of air flow on drawdown of hydraulic heads in the aquifer and parameter estimation is also explored in this part.

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