Analysis And Prediction Of Water And Salt Dynamic In Groundwater Under Drought Condition

Qingtongxia Irrigation District locates in the arid and semiarid region of northwestern China. Due to the lack of rain climatic conditions and the agricultural custom of spate flooding irrigation in a long time, there are some serious soil and water environment problems appeared in the irrigation district, and the soil salinization which is the main obstacles to the agricultural production and sustainable development of Qingtongxia irrigation District is one of them. The dynamic of groundwater and salt is the main properties and form factor, so finding out the dynamic characteristics and change rules of groundwater and salt is very important to the prevention and control of soil salinity in irrigation district.The paper will take the water and soil environment (soil salinity) in Qingtongxia Irrigation Distract as the research object, analyze and predict the dynamic characteristics of groundwater and salt based on systemic analyzing previous data of groundwater and salt in irrigation district and predecessors' achievements. The specific content as follows:(1) According to the soil salinity problem in Qingtongxia Irrigation District, the paper summarize the research progress of groundwater-salt transports, groundwater and soil salinity dynamic prediction model, analyze the advantages and disadvantages of existing research methods and research results, thus puts forward the research content, method and technology route.(2) The paper summarizes the status of salinity soil in Qingtongxia Irrigation Distract, and analyzes the factors of its formation.(3) The paper analyses the dynamic types of groundwater in Qingtongxia Irrigation Distract, and discusses emphatically the dynamic characteristics and change rules of groundwater and the dynamic characteristics of groundwater mineralization according to the previous groundwater material. The results show:①The groundwater level in one year of irrigation district exists the obvious seasonal change rules, in another words, it will rise in irrigation season and continually decline in non-irrigation season, and rise again in irrigation season of the next year; The groundwater level exists similarity between the many-years, it is in a stable state periodically, and the average groundwater depth changes in the range of 1.64~1.75m.②The water quality is bad with the increasing change rules of groundwater mineralization from west to east and from south to north, it exists same change rules with the irrigation season, the highest groundwater mineralization appeared in April generally, and the lowest groundwater mineralization appeared in June,August or November.(4) The paper analyzes the dynamic of soil salinity and the relation between soil salinity and groundwater. The result shows that the transport of groundwater-salt has obvious seasonal characteristics for years; the salt accumulates in spring, deposites in irrigation season and autumn and reserves in winter, and it exists similarity between the many-years.(5) Combining the BP neural network and the time sequence method, and taking the observations average annual underground water depth of 1985～2000 in irrigation as the time series data, I establish the Qingtongxia irrigation distract based on BP Neural Network of underground water level dynamic time series prediction model, and edit routine by MATLAB7.0 for predicting the groundwater level changes of Qingtongxia irrigation distract in 2015 and surface soil salinization changes. The results show that the groundwater lever will drop in 2015, and the surface soil will be sallity lighter, Qingtongxia Irrigation Distract will develop healthy by lighter soil salinization disaster.