Submarine groundwater, an alternative source of water supply for Hong Kong?

Abstract

Hong Kong imports about 70% of the drinking water from East River via an 83 kilometer closed aqueduct. The spectacular industrial and population growth of cities along and near the river catchment has made them into both major polluters and competing consumers over the river water. To find another source of drinking water for Hong Kong, the Hong Kong Government has again began to looking into desalination as a serious supply alternative. It is hypothesized that submarine groundwater below the seabed may be another possible source of water supply for Hong Kong. It is well known that fresh or relatively fresh groundwater may exist below the sea in some coastal areas due to complex geological environment and history. The sea level around Hong Kong has fluctuated significantly in recent geological time and the shallow seabed was then elevated and exposed to the ground many times. In about 10,000 years BP, the sea level was about 100 m below the current sea level and the coastal line was about 100 km away from the current coastal line. It is believe that the aquifers which are now below the current seabed but once exposed above the palaeo sea level may still preserve fresh groundwater or blackish water with salinity much lower than current sea water. The typical geological profile from top to bottom in coastal HK sea consists of soft marine mud, hard clay and sand and gravel aquifers and decomposed igneous rock. The aquifer thickness can be up to 50 m. The low-permeability mud and clay with thickness of up 20 m overlying the aquifers may effectively impede the hydraulic connection between the seawater and underlying groundwater and preserve the fresh water in the aquifers. Such a water resource may be used at least in times of emergency. Even the water is not fresh enough to be directly drinkable, desalination of the blackish water may be much cheaper than that of the seawater.