Coastal Region Of The Lower Reaches Of The Yangtze River Underground Pipe Down Stains Desalination Technology

The job of agricultural drainage is to accelerate removing of the excessive water and salt in soil,control the underground water table at favourable depth,so that it can assure crops growing well and avoid salinization. PVC subdrainage is one kind of advanced drainage techniques developed in recent years in the world. It will have a promising future of wide application.This paper studied the effect of soil water content on barley at different growth stages,through the study,we found the sensitive stages of barley to water and salt is the stem elongation and spike formation stages. Based on this,the upper controlling index of soil water content is 80.4% and the days of waterlogged and salinization tolerance is 3.2 days.The moisture and salinization movement mathematical model in the field under subdrainage condition is based on the assumption of neglecting the effects of horizontal hydraulic gradient,It can analogy the changes of soil water content and salinization which are changed with times and depth. Compared with the reality,it shows that this model and its parameters are defined reasonablly. To analyse the arrangement of drainage system with different spacings and depths,with unsteady flow formula and benefit index,this paper gives a two-dimensional non-linear programing model for arrangement of drainage system in the barley field,which can be solved by the Method of Projected Gradient.By this model,we make out the optimum solution of spacings and depth of PVC pipe in littoral area of Changjiang River that is S=21.5 8m,h=l.lm. Because of being given to both the growth demand of crops and engineering cost,this model can be applied on actual conditions.