Effectiveness of groundwater extraction in Beijing since the ingauration of the first phase of the South-to-North Water Diversion Project, China

This study assess the effectiveness of groundwater pressure extraction in Beijing since the opening of the first phase of the South-to-North Water Diversion Project,using survey and evaluation methods.Firstly,an analysis of water consumption structure and the usage of diverted river water in Beijing in recent years was conducted.Secondly,the volume of groundwater pressure extraction in Beijing after the 33 project's inauguration was examined,revealing a decrease from 1.96 billion m^(3) in 2014 to 1.35 billion m^(3) in 2020.The proportion of water supply reduced from 52.3%in 2014 to 33.3%in 2020,leading to an optimized water supply structure.By the end of 2020,groundwater pressure extraction in Beijing is estimated at 446 million m3,with a substantial reduction in over-exploitation of groundwater.Groundwater resources have been effectively replenished,and the strategic reserve capacity has been enhanced.Furthermore,this study evaluates the change in groundwater levels as an indicator of the effectiveness of pressure extraction.The declining trend of groundwater levels in Beijing has been effectively mitigated,and there has been a consistent rebound in groundwater levels over the past five years.

Land subsidence induced by groundwater extraction and building damage level assessment—a case study of Datun, China

As in many parts of the world, long-term excessive extraction of groundwater has caused significant land-surface sub- sidence in the residential areas of Datun coal mining district in East China. The recorded maximum level of subsidence in the area since 1976 to 2006 is 863 mm, and the area with an accumulative subsidence more than 200 mm has reached 33.1 km2 by the end of 2006. Over ten cases of building crack due to ground subsidence have already been observed. Spatial variation in ground subsi- dence often leads to a corresponding pattern of ground deformation. Buildings and underground infrastructures have been under a higher risk of damage in locations with greater differential ground deformation. Governmental guideline in China classifies build- ing damages into four different levels, based on the observable measures such as the width of wall crack, the degree of door and window deformation, the degree of wall inclination and the degree of structural destruction. Building damage level (BDL) is esti- mated by means of ground deformation analysis in terms of variations in slope gradient and curvature. Ground deformation analysis in terms of variations in slope gradient has shown that the areas of BDL III and BDL II sites account for about 0.013 km2 and 0.284 km2 respectively in 2006, and the predicted areas of BDL (define this first) III and II sites will be about 0.029 km2 and 0.423 km2 respectively by 2010. The situation is getting worse as subsidence continues. That calls for effective strategies for subsidence miti- gation and damage reduction, in terms of sustainable groundwater extraction, enhanced monitoring and the establishment of early warning systems.

SAR-based Subsidence Monitoring and Assessment of the Factors Involved in the Occurrence of Subsidence,Lahore City

The judicious use and management of natural resources is vital to achieve sustainable development.Land and water are prime natural resources,and their depletion and degradation can lead to serious threats like land subsidence.Land subsidence is a phenomenon of the alteration of elevation at a point on the earth through the sinking of the surface.It occurs when the earth’s surface loses its support.The major causes of land subsidence include groundwater extraction,mining,construction overload,and other similar factors that increase pressure on the surface and eventually subsidize the land.Urban centers with excessive groundwater extraction and infrastructure development are at a high risk of subsidence.Lahore,the second-largest city in Pakistan,is undergoing an enormous increase in population density,uncontrolled urbanization with very large-scale construction projects,and intensive groundwater extraction which are responsible for subsidence directly or indirectly.Therefore,studies on groundwater status and unplanned urban appraisals have seriously urged monitoring of the subsidence in Lahore.Herein,we used freely available Sentinel-1 data for one year(from August 2018 to August 2019),with a high spatial and temporal resolution,to monitor subsidence in Lahore.The data were processed using the SNAP/Sta MPS approach for Persistent Scatterer Interferometric Synthetic Aperture Radar(PSI)analysis,which is an advanced InSAR technique.The displacement velocity map from InSAR processing shows a significant land deformation in the area with values ranging from-114 to 15 mm yr^(-1).Along with the Sentinel-1 data,we also used supplementary data obtained from various government agencies of Pakistan to study the land cover map,transportation network and waterways of Lahore,soil types,population density,and field points for assessing the results and understanding the roles of various factors in the occurrence of uplift or subsidence.A strong correlation was established between subsidence and various parameters such as groundwater extraction and lowering of the water table,soil type variations,land cover changes,surface water channels,and population density.The deformation map confirms the greatest subsidence in the central part of Lahore,while the uplift is observed in the less populated and rural areas situated near Ravi River.The land subsidence and uplift could be attributed to groundwater extraction and recharge through the canal system and the river,respectively.