Research On Evolvement Of Shallow Groundwater System Impacted By Exploiting In North China Plain

For long-term and large amount exploitation in North China Plain, the groundwater system and its circling order have been disturbed, resulting in the amount and and quality of groundwater resource being changed greatly, and environment problems become severe more and more. So it is significative to study the evolving characteristic and change of hydrogeologic parameters, which is helpful to provide scientific supervision for rational utilizing of groundwater.Being supported by Investigation and Estimation of Groundwater's Continuable Utilization Potential in North China Plain, it is studied in this paper that the evolving characteristic of shallow groundwater system, from recharge, runoff, discharge, dynamical field of groundwater, and hydrogeologic parameters. And discussion is given about mechanism of influence to groundwater system's evolving by exploiting. The specific yield's change in fluctuation belt of water table is researched as one of emphasis, and its distribution maps are gotten in different exploiting period of time by utilizing modern software tools. Analysis of precipitation infiltration coefficient's change is the other emphases of this thesis. Field experimentation is taken, in which amount of precipitation infiltration and coefficient are calculated utilizing Natural Chloride Ion and Artificial Tritium Tracer Method under thick unsaturated zone.The results indicates that the years average equilibrium difference between recharge and discharge is -21.76×108m3/a, resulted from cosmically and high strength exploitation and resulting in water table's coming down persistingly. The decliner extent of shallow groundwater table from in 1959 to in 2003 is 20～40m in most region of piedmont plain, while in part of is astonishing 60～70m; And 1～10m in most region of mid plain, while 10～15m in part of; And 1～5m is the dominating in coastal plain. As a result of the great decliner, the groundwater system's recharge, runoff and discharge have evolved from charactered with rain-evaporation to with exploitation; and the natural flow field charactered with flowing from piedmont to coastal plain have changed into the new charactered with exploitation, and of which groundwater decrease cones as the convergers. Corresponding with unsaturated zone becoming thicker, going with the depth of table becoming deeper, some correlative hydrogeologic parameters are changed. Change extent of specific yield in fluctuation belt of water table is greater in piedmont plain, primarily in 0.018～0.06 and part of beyond 0.072, than in mid and coastal plain, in -0.018～0.018. Phreatic evaporation coefficient is approximate to 0 in most of piedmont plain, while become some greater in irrigating region along Yellow River. The result of feed coefficient of precipitation infiltration is 0.158 in Zhengding Proving Ground, almost no diminishing contrasted with 0.16 in 1980s, while 0.082～0.219 in typical districts of mid and coastal plain. In conclusion, cosmically and high strength exploitation, which resulted in shallow groundwater table's descending and the system's acutely evolving, is the primary factor that bring on hydrogeologic parameters'change and hydro-geological environmental problems.