Opportunities And Challenges Of Cooperation Between China And Algeria In The Mining Secto

The most important factor causing land subsidence is the overexploitation of groundwater.Groundwater exploitation for different purposes leads to different modes of land subsidence,among which the proportion of groundwater exploitation for agricultural irrigation is the largest（about 80%）.As one of the main production areas of winter wheat in China,the North China Plain is experiencing serious land subsidence,especially in Hengshui City.At present,there are no studies to make a reasonable analysis of the large-scale land subsidence model in Hengshui City.In this context,this paper combined InSAR and independent component analysis methods to analyze the ground subsidence model of Hengshui City.Based on the separated data of different ground subsidence components and water head changes,the changes of groundwater reserves that cause ground subsidence are quantitatively described.Specific research contents and results are as follows:（1）For the first time,a wide range of InSAR time series data and independent component analysis method were combined to separate the land subsidence models of Hengshui City from a global perspective,revealing the three main contributing components of land subsidence and their spatiotemporal characteristics,which provided the basis for effective prevention and control of land subsidence in Hengshui City.The first independent component（IC1）represents the irrecoverable long-term settlement caused by long-term groundwater overextraction.The time series showed a continuous downward trend,and the main spatial contributions were distributed in areas with severe groundwater exploitation,such as vegetable greenhouses and cultivated land far from water sources.This component is the main sedimentation model in Hengshui City.The second independent component（IC2）represents the subsidence caused by urban industrial and domestic water use,and the time series shows a trend of first decreasing and then increasing,and the spatial distribution is mainly in urban areas with high urbanization,such as Taocheng District and Jizhou District.The urbanization rate of each county and city,industrial water withdrawal and IC2 contribution value have high correlation coefficients（0.79 and 0.7）,which proves the existence of this component.The third independent component（IC3）represents seasonal subsidence,and the time series presents a cyclical trend,with a downward trend in winter and spring（February to June）,an upward trend in summer and autumn（July to January）,and the peak and trough values appearing in February and July respectively.This seasonal subsidence is directly related to groundwater extraction for winter wheat irrigation.IC3is mainly distributed in areas with obvious groundwater fluctuation,such as Taocheng District,Wuyi County and the north of Shenzhou City.The IC3 time series is highly correlated with the periodic components of the monthly variation of groundwater level,and it is found that IC3 lags the variation of groundwater level by 9-30 days.（2）Based on the results of independent component analysis,the change of groundwater reserves in Hengshui City from 2017 to 2019 was quantitatively estimated,providing an important basis for the scientific utilization of groundwater resources.The elastic bone water storage coefficient(S_ke)of Hengshui City was estimated from the elastic ground settlement and elastic change of water head,and combined with InSAR ground settlement,the recoverable and unrecoverable groundwater storage changes were estimated.The results show that the permanent loss of groundwater in Hengshui City increased gradually from 2017 to 2019,and the permanent loss of groundwater reserves in 2019 was the most serious,about 7.31×10⁸m³.The total permanent loss of groundwater in three years is 19.52×10⁸m³,and the average annual loss is about6.51×10⁸m³.The unrecoverable groundwater changes account for more than 98%of the total groundwater changes.