By Brett Walton
15 June 2016
(Circle of Blue) – Beijing, one of the world’s most water-scarce large cities, has long drawn on groundwater reserves to supply more than 20 million people. The unrelenting pressure for water, though, is causing the land to shift and sink and buckle, which puts subway and high-speed rail lines, buildings, and other infrastructure at risk of damage.
If the region’s water-related land shifts, technically known as “subsidence,” go unchecked, severe consequences could be in store. Scientists at a railway engineering laboratory at Beijing Jiaotang University concluded in a September 2015 study that groundwater pumping must be restricted near completed high-speed rail lines and that new wells near the lines should be prohibited.
The trains, which reach speeds of more than 300 kilometers (186 miles) per hour, require stable tracks to keep the cars from derailing. The high-speed lines from Beijing to Shanghai and Beijing to Tianjin, a heavily populated port city, both pass through the Chaoyang subsidence zone east of Beijing. The researchers said that continued subsidence will have a “strong impact on the safety of train operation.”
According to satellite measurements, the Beijing region is sinking at an increasing rate as the soil of the North China Plain, like a sponge wrung dry, compacts around depleted aquifers. The data were published earlier this month in the journal Remote Sensing.
A common symptom of voracious groundwater use, subsidence is taking a toll on the world’s largest urban areas. More than 50 Chinese cities are grappling with uneven soils. In Southeast Asia, Bangkok, Ho Chi Minh City, and Manila are all sinking. Parts of Jakarta, the Indonesian capital, are dropping as rapidly as Beijing’s Chaoyang district. [more]
ABSTRACT: Beijing is one of the most water-stressed cities in the world. Due to over-exploitation of groundwater, the Beijing region has been suffering from land subsidence since 1935. In this study, the Small Baseline InSAR technique has been employed to process Envisat ASAR images acquired between 2003 and 2010 and TerraSAR-X stripmap images collected from 2010 to 2011 to investigate land subsidence in the Beijing region. The maximum subsidence is seen in the eastern part of Beijing with a rate greater than 100 mm/year. Comparisons between InSAR and GPS derived subsidence rates show an RMS difference of 2.94 mm/year with a mean of 2.41 ± 1.84 mm/year. In addition, a high correlation was observed between InSAR subsidence rate maps derived from two different datasets (i.e., Envisat and TerraSAR-X). These demonstrate once again that InSAR is a powerful tool for monitoring land subsidence. InSAR derived subsidence rate maps have allowed for a comprehensive spatio-temporal analysis to identify the main triggering factors of land subsidence. Some interesting relationships in terms of land subsidence were found with groundwater level, active faults, accumulated soft soil thickness and different aquifer types. Furthermore, a relationship with the distances to pumping wells was also recognized in this work.