海河平原东部地区地面沉降机理与趋势

Mechanism and trend of land subsidence in the east Haihe River Plain

海河平原东部地区是中国水资源最紧缺的地区之一。地下水开采量占该地区供水总水量的60%以上。深、浅层地下水超采量均超过500亿m3。该区也是山前拦蓄地表径流最高的地区,大小水库达1820多座,拦蓄能力320亿m3,控制山区流域面积近90%。在地下水补给源减少与大规模超采地下水的综合作用下,造成平原区河流干涸、地下水水位持续下降、含水层疏干及地面沉降等环境地质问题。同时诱发了含水层之间强越流渗透以求动力场平衡问题,第四系松散地层出现垂向压密而导致地层塑性变形。在滨海平原区,区域性地层垂向压密变形存在缓慢发展趋势。研究表明,地面沉降致灾过程至少存在3个阶段,即自然沉降机制阶段、缓变劣变质变阶段以及快速衰变破坏阶段。缓变劣变质变阶段是采取措施减灾最佳时期。

The east Haihe River plain area is one of the regions which are short of water resources in China.The groundwater withdrawal amount is more than 60 percent of the total water supply amount in this area.The groundwater extra-exploration amount of both deep and shallow aquifer exceeds 5 billion m^3.At the mean time this area is the region which blocks the most land surface water of the mountain zone.There are more than 1820 reservirs in this area.The sluice ability is 3^2 billion m^3.It controls about 90 percent mountain zone valley area.The reduction of groundwater supply and large amount of extra-exploration of groundwater includes many environmental and geological problems such as river drying in plain area,continual decline of groundwater level,dredge of aquifer,land subsidence and so on.At the same time this induces the strong leakage penetrate of aquifers in order to achieve dynamic balance and plastic deformation induced by vertical compression of Quarternary loose strata.The study indicates that land subsidence inducing hazards includes 3 phases:natural subsidence phase,slow qualitative change phase and fast disintegration collapse phase.The slow qualitative change phase is the best period to reduce hazard.