地下水位升降和抽水对海水楔影响的实验研究

为掌握滨海地带无压含水层中的海水楔因地下水位升降及抽水引起的移动规律,采用室内实验的方法,考察了海水楔在不同的水面坡度和抽水位置下的移动特性.通过改变水面坡度的方法探讨了海水楔侵入和后退的规律.在入侵时,海水楔在形成明确的咸淡水界面的同时向着内陆移动.水面坡度越小海水楔内陆入侵的范围越大,达到平衡状态所需要的时间越长.海水楔后退时的速度比侵入时快,且海水楔后退后其入侵过的区域能完全恢复到入侵前的状态.在海水楔外部抽水初期,海水楔的长度略有减小.在此之后其长度急剧增加,但随着平衡状态的接近,这种增长率逐渐变小.抽水引起的咸淡水界面的隆起位置位于抽水位置和咸淡水界面的最短距离处.抽取的地下水中海水的比例随着抽水位置与海水楔的接近会急剧增大.在海水楔内部抽水时,海水楔的长度随着时间呈指数函数的关系减小,且较外部抽水时到达平衡状态时所需要的时间短.此外,还给出了能预测因地下水位的升降引起的海水楔前进和后退的数学模型.

Fluctuation in addition to the ground-water over-pumping

This paper takes as its target at exploring the regularities of the seawater wedge encroachment and attacking influence on the coastal line groundwater level change through laboratory experiments. As a matter of fact, the fluctuation of ground water level and agro-use and drinking water pumping in the coastal areas has greatly affected the non-compressive aquifer and the moving features of seawater wedge under different hydraulic pressures and water-pumping positions. Firstly, seawater encroachment and receding through water surface changing gradients can be observed experimentally in such areas. To be exact, during the initial stage, seawater wedge moves toward the inland while fresh-salt water interface has been formed, which takes on a linear shape. In later stages, the bounding line changes like a down-convex parabola. The less the water head drops between the groundwater surface and the sea-water level, the greater the encroaching scope of the wedge will be, and the longer it takes the time to reach equilibrium. However, on the whole, the wedge actually recedes more quickly than it encroaches, and in turn it is more likely for the encroached area to get fully recovered after the encroachment. Secondly, the effect of pumping and the pumping position on the changes of seawater wedge through pumping tests can also be observed through the experiments. If the tests are done outside the seawater wedge, the length of the wedge drops a httle bit initially, then rises rapidly at an increasing rate and declines slowly till the approaching equilibrium forms. The bulging position of the fresh-salt water interface under the pressure of the pumping lies in the point nearest to the pumping position. However, the wedge moves more quickly when pumping is carried out downstream than upstream from the wedge. For the pumping position, the more close to seawater wedge is, the higher the salt content in water pumped will be. Therefore, there will be a distance between the pumping position and the fresh-salt-water interface to ensure the salt content in ground water is low enough to meet the water supply standard. When pumping is carlied out in seawater wedge, length of the wedge will decrease with the time going on by the exponential function, and the time to reach equilibrium would be shorter than that of being outside the wedge. The research also builds a mathematical model to predict the encroachment and receding of seawater wedge, which may be brought about by the fluctuation of ground water level.