Modification of Groundwater Regimes in Coastal Areas due to Extensive Urbanization

Abstract

Hong Kong has been well known for "concrete jungle" and a majority of the total 6.7 million people reside in a narrow strip of less than 1 km from the sea. The construction of the buildings and underground transport systems usually requires extensive foundation and ground engineering work, including deep excavation, bored piles, grouting, and diaphragm walls. It is believed that the natural soil in the shallow depth of tens of meters, which is usually a zone with the most active groundwater movement, is largely replaced by impermeable concrete materials. A review of the historical information indicates that numerous springs located in the lower part of the hillslope of Hong Kong Island were extinguished in the process of urbanization. An examination of the piezometric data in the urbanized areas shows that the groundwater flow is sluggish and has only weak hydraulic connection with the recharge area at the natural slope. A groundwater flow numerical model along a typical section is established and calibrated by comparing the simulated water levels with the observed ones. The modeling results show that the overall hydraulic conductivity in the shallow zone of the lower part of the slope is about one order of magnitude lower than that in the upper natural slope. The significant decrease in the hydraulic conductivity may reflect the modification of the natural aquifer system due to deep foundations of the extremely crowded buildings in the urbanized area.