| Large numbers of people shifted from inland cities to coastal cities because of the rapid development of social and economic in coastal regions. And this phenomenon leads to the shortage of land in coastal areas, so land reclamation has become one of the important methods to solve this contradiction. The land reclamation project leads to the rise of groundwater level in the original land regions. The initial groundwater of reclamation came from the capillary rise of seawater which has a high salinity, and it rises to a relatively stable state after the gradually transition of the groundwater in the original land area. Therefore, land reclamation also brought a series of entironment problems such as high salinity of groundwater and soil salinization when it has become a method to solve the land shortage in the coastal regions. In this paper, to analysis the mechanistic problems of such cases, after numerous investigations of land reclamation project aroundBohai areas, a model of land reclamation was constructed using the FEFLOW software to simulate the groundwater flow and salt transport situation. Then simulate the case when adding some measures which have the ability to dilute salt, analysis the effect of prevention and control measures by calculation, and give some recommendations for improving the situation. The main research contents and conclusions of this paper are as follows:(1) First, compare blowing sand reclamation with riprap reclamation in the aspect of construction methods, applicable conditions, soil structure and coastal types. Then make a summary of soil structure, plant types and chemical characteristics of groundwater in riprap reclamation regions after investigating and analyzing Lingshui Bay of Dalian.(2) By analyzing the reclamation fill types and structures, combining the correlation coefficient from physical experiments from the research of our group and level observation data from observation wells of the original land area, a conceptual model was set up which is conformity with the practical background, then simulate the trend of groundwater and salt transport in the five years after the completion of the reclamation project. The results show that the background of simulation region has a strong evaporation capacity and small precipitation, the situation is very serious that there is no fully groundwater recharge, salt can not be diluted and salt in the soil also can not rinsed when the model under the condition of rainfall infiltration and evaporation excretion.(3) Analysing the change degree of groundwater level and chloride ion concentration under the influence of this parameter by making a rainfall infiltration coefficient sensitivity analysis of ± 10% and ± 20% change. The results show that the change of rainfall infiltration coefficient can lead to a certain extent of ground water level. But the little changes of infiltration capacity can not reverse the severe situation under the background of small precipitation and strong evaporation capacity. Therefore, it is a good choice to add the rainfall infiltration by changing land-use situation. But in order to achieve the goal of leaching salt, raising the level of groundwater and relieve the seawater intrusion tension, other measures must be taken at the same time.(4) Analysing the of degree of improvement of groundwater environment under different measures by simulating rainwater collection and utilization measures, so as to provide reference for the reclamation project around Bohai Sea to take some relevant measures. The results show that when taking the freshwater recharge measure, the amount and position of recharge is very important which have significant effect on the desalination of the salt. The construction of underground diaphragm wall can effectively regulate underground storing and improve water quality. The improvement will be more obviously when taking the underground diaphragm wall and recharge wells at the same time especially for the area where the groundwater level is lower. |
PDF Full Text Request