Preliminary studies on physical and chemical processes in the subsurface system in the land reclaimed from the sea

Land reclamation has played a significant role in the urban development process in coastal areas in many countries. Over the last 20 years, land reclamation has gained much popularity especially along coastal areas of the south and east China due to rapid development of industry and urbanization. While reclamation provides valuable land, it also creates various engineering, environmental and ecological problems in coastal areas. The direct impact of land reclamation on coastal engineering, environment and marine ecology is well recognized and widely studied. However, it has not yet been recognized that reclamation may change the regional groundwater regime, including groundwater level, interface between seawater and fresh groundwater, and submarine groundwater discharge to the coast. There may be various chemical reactions between the fill materials and the marine mud. These processes may result in chemicals which may have adverse effect to the coastal plants and organisms. This paper presents respectively two preliminary case studies about the possible modification of the regional flow system at Penny’s Bay, Hong Kong due to land reclamation and the possible chemical reactions in the reclamation site at Shekou, Shenzhen. This paper predicts the change of groundwater system around the bay area in response to the land reclamation and the possible pathway of the contaminated groundwater below Cheoy Lee Shipyard located on the north-eastern shores of Penny’s Bay. After reclamation the total groundwater head in the entire model area is increased. Due to the change of the flow system after land reclamation, the contaminated groundwater near the shipyard will not spread out much within Penny’s Bay, as many people expected, but migrate northeast toward the opposite coast. At the Shekou site, the fill materials, which are largely reddish or brown decomposed granitic rock excavated from nearby hills, are dumped over the grey to dark marine mud at the sea bed. Because the coast line is extended seaward, the original seawater and groundwater interface will also move seaward accordingly. The alkaline seawater initially in the site will be gradually displaced by acidic groundwater. It is hypothesized that various chemical and physical reactions will occur in the site. These reactions may release chemicals which may have adverse effects on coastal water quality and environment. However, further studies are required to investigate these hypotheses.