Study On Rules Of Groundwater And Salt Dynamic Change In Luohui Canal Irrigation District

With the rapid development of irrigation agriculture in China, the irrigation area has been increasing continuously. However, the unreasonable exploitation and utilization mode and insufficient management pattern of water resources in irrigation districts have resulted in many serious local eco-environmental problems such as soil secondary salinization and alkalization, land desertification and groundwater quality deterioration. According to the serious problem of soil secondary salinization and alkalization reappeared in Luohui canal irrigation district in the past several years, by using the integrated methods such as field observation well on-site observation, field investigation and indoor experimental analysis on water samples and soil samples and so on, the groundwater water chemical properties and groundwater salt heterogeneity as well as the effect of groundwater table on groundwater water chemical properties were analyzed detailedly in the paper. In addition, the groundwater table and groundwater water quality and soil properties in Luohui irrigation district in the coming fifteen years were also predicted in the paper. The obtained results in the paper are of great importance to groundwater dynamic regulation and control, rational groundwater water resources utilization, etc. The main study contents and conclusions are as follows:Firstly, the exiting situation and reasons of the soil secondary salinization. The results showed that, the soil salt content is high in the north area while low in the south area of the irrigation area, and the soil salt content is high in the middle area while it is reduced gradually towards the both edges of the irrigation area, as a result, the soil salt content presents a fan-shaped spatial distribution characteristics in the irrigation area. However, compared with the soil salt content, the soil alkali degree presents a irregular spatial distribution characteristics in the irrigation area. In addition, the soil salt in the irrigation district is mainly composed ofsulphate and carbonate of sodium (potassium) and calcium, which indicated that the soil in the irrigation district has already been alkalized.Secondly, the analytical method of groundwater chemical composition, i.e.H.и.Τοлстнхинgraphic classification method was adopted to analyze the groundwater chemical compositions in the irrigation area, as a result, the groundwater chemical type in the irrigation district belongs basically to sodium chloride - sulphurate sodium type groundwater. In addition, according to the calculation results on groundwater sodium adsorption ratio and magnesium coefficient, the groundwater in the most area of Luohui canal irrigation district has an adverse effect on the growth of the crops and could lead to potential soil alkalization.Thirdly, according to the observe data from the observation well network in the irrigation district, by using space heterogeneity theory, the effects of groundwater table on groundwater conductance in different period and under different spatial distribution conditions were analyzed mainly. The resulted indicates that, there is a close relationship between groundwater conductance and groundwater table, and the relationship has a strong regional characteristics, i.e., the value of groundwater conductance in the terraces of the irrigation district increases with the rising of the groundwater table, and the high value of EC appears in the terraces with high groundwater table and the groundwater conductance in the No.1 terrace has a distinct variation characteristics.Fourthly, a bivariate linear regression model of groundwater table was obtained, through which the variation tendency of groundwater table in the irrigation district in the coming fifteen years was predicted, and the corresponding future variation tendencies of groundwater quality and soil properties were also predicted. The results shows that, the groundwater table in the irrigation area will fall gradually in the following 15 years, and the groundwater water quality will keep in a better condition, which will not lead to soil salinization and alkalization. Finally, according to the present situations of the irrigation district, the basic approach and thought for water salt regulation and control in the irrigation district was proposed in the paper, i.e. rational water diversion from Luohe river, rational groundwater exploitation, rational determination of the ratio of canal irrigation water amount to well irrigation water amount, rational control of total discharged water amount and detrimental or harmful salt amount and strict control of groundwater table under the critical buried depth, etc. Meanwhile, the principles such as adhering to the overall viewpoint and paying emphasis on water-saving.