On the Main Factors Controlling Anthropogenic Land Subsidence in the Northern Plain of the Chaobai River, North Beijing, China
Wednesday, 17 December 2014
Anthropogenic land subsidence is a widespread phenomenon threatening several cities in China. One major area of land subsidence is the Beijing city. The city continues to grow and unofficial estimates put the population at around 21-22 million in 2013, with an increase by 40% from 2000 to 2010. Along with the increasing urbanization, demands for water resources become larger. Approximately 2/3 of the water need is supplied by groundwater. To cope with the pressure for water supply, a first “over-sized emergency groundwater resource region (EGRR)” was built in 2003 at the Huairou district, where is the upper and middle plain of the Chaobai River, few tens km to the north of the metropolitan center. Other four EGRRwell-fields have been established in different districts surrounding the city in the next years. The long-time over-exploitation of groundwater resulted in water level fall and land subsidence. Persistent Scatterer Interferometry (PSI) on ENVISAT images has been used to detect land subsidence in the northern Beijing plain from 2003 to 2010. The PSI outcome, which was calibrated using ground-based measurements including levelling and extensometers, reveals that the largest subsidence rate reached 52 mm/yr, with a cumulative maximum sinking equal to 342 mm, in the Houshayu city at the southwestern part of the study area where the capital international airport is situated. Land subsidence in the northern zones, where the main well-fields are located, was much smaller in the order of 60 mm. Hydro-geologic investigations have showed that the distribution of groundwater depression cones only partially resembles the land subsidence pattern. The subsidence rates are strongly correlated with the distribution of compressible clay units. In the south-westernmost zone, at the bound of the metropolitan area, the cumulative thickness of cohesive soils amounts to 250 m in the upper 390 m sedimentary sequence. Conversely, sands and gravels prevail in the northern portion of the plain.