Study On Dynamic Simulation Of Water And Salt And Sustainablity Strategy In Hetao Irrigation District

The Hetao Irrigation District(HID)is a typical arid irrigated region in the upper Yellow River basin.It is an important food production area,where irrigation is essential for agriculture.The increasing water scarcity and non-agricultural water consumption have become the great limitations to the development of sustainable agricult'ure and eco-environment.Thus,the water conservation and water-saving practices should be implemented for alleviation of water scarcity.The water distribution,crop planting and salt distribution have changed accordingly with the change of water supply,these changes will have a certain impact on the hydrological cycle and the ecological environment of the regional scale.Therefore,studying the water-salt dynamics and water-saving ecological environment effects are helpful to realize the high efficient utilization of water resources and sustainable development of ecological resources.In this thesis,the statistical analysis,model simulation and GIS methods are used to quantitatively estimate the dynamics migration trend of regional soil salinity,to qualitatively analyze the main influence factors of the salt concentration of the Wuliangsuhai water based on the field investigation,regional data collection,and field monitoring experiments.Then the regional water and salt dynamics of the various water management measures have been analyzed according to the simulation results.In addition,the threshold of ecological environment water demand of Wuliangsuhai was considered,and a suitable irrigation and drainage development modes are proposed.Main contents and conclusions are as follows:(1)The soil salinity dynamic migration and the main influence factors in regional scale have been estimated and analyzed.The results showed that the annual salt accumulation is 571200 t/y,39.7%of which accumulates in 1-m-deep soil layer and the rest migrates to deep soil or groundwater.The soil salinity of 1-m-deep soil layer decreases by 11.21%in the cultivated land,while increases by 235.62%in salt wasteland.The salt has a tendency to migrate from cultivated land to salt wasteland.The groundwater depth,drain discharge and annual evaporation have greatest impact on soil salinity,followed by salt concentration of groundwater,irrigation water and rainfall.Stepwise regression analysis indicates that the soil salinity of the 1-m-deep soil layer in the cultivated land is significantly related to groundwater depth.(2)The main influence factors of the salt concentration of the Wuliangsuhai water was been analyzed.The results showed that the salt concentration of groundwater,drain discharge,the amount of water discharged into the Yellow River,salt concentration of the drain discharge,discharge of sewage and ecological amount of water replenishment have the greatest impact on the salt concentration of the Wuliangsuhai water,followed by rainfall and evaporation.The established prediction model has certain representativeness.(3)The Jiefangzha Irrigation System(JFZS)of the Hetao was used as a case study for analyzing the soil salinity dynamic of the cultivated land and salt wasteland under different water management measures.The root zone salinity of the cultivated land decreased by 1.03%after 10 years,whereas the salinity significantly increased in the salt wasteland.The salt wasteland has great potential for the distribution of salinity in the irrigation area.After comprehensive consideration of salt control,crop water demand and water saving effect,the simulation show that the summer irrigation water was decreased by approximately 15%,and the autumn irrigation water was increased by approximately 10%based on the present irrigation conditions.Furthermore,the soil salinity will decrease by approximately 6.2%,and the total irrigation water will decrease by approximately 95 m3/hm2.(4)Taking the entire Hetao Irrigation District as a case study,the distributed model(SahysMod)and GIS are combined for simulating study.Firstly,the study was divided into 299 unif'ormly distributed grid units.Then the model was calibrated and validated based on the monitoring experiments.The results showed that the distributed model(SahysMod)can take into account regional spatial variability and has a good potential for simulating long-term water and salt dynamic simulation on a regional scale.In the calibration period,the root mean square error RMSE of groundwater depth is between 0.17-0.55m,the average relative error MRE is between-1.35%?12.84%.In validation period,the RMSE is between 0.22-1.35m,and the MRE is-8.14%?31.07%.The relative error RE of annual drain discharge is between 0.30%and 9.08%,the determination coefficient is 0.945.The average RE is 6.83%of the salt concentration of the drain discharge.(5)The regional water and salt dynamics of the various water management measures were been analyzed based on validated SahysMod model.The results showed that the change of drain discharge and groundwater depth are relatively stable,the salt concentration of the drain discharge has a slightly increasing trend,and the salinity of cultivated land in the moddle and upper reaches of the irrigation area shows a slight decrease trend,while the salinity of cultivated land in the lower reaches of the irrigation area has a significant increase trend in the next 10 years under the current irrigation and drainage conditions.When total water diversion is reduced,the amount of water discharged into Wuliangsuhai is reduced,and salt concentration of the drain discharge is increased,which will have a certain impact on the salt concentration of the Wuliangsuhai water.In reality,it is necessary to comprehensively consider the minimum ecological water demand and the actual ecological amount of water replenishment for maintaining the ecological health and environmental safety of the Wuliangsuhai,although a certain amount of water can be saved through various measures.In the future,if the total water diversion continues to decrease,if the water utilization coefficient of the canal system remains unchanged,it is necessary to improve the water saving efficiency by improving the field water saving technology or adgusting the palating structure.The total water diversion from the canal system can be reduced by up to 15%,and the water consumption can be saved up 650 million m3 compared with the current value.Improving the field water saving measures or adjusting the planting structure can be prioritized to consider for reducing the amount of field irrigation during the growing period,when the water saving level is low.While the filed water saving measures and channel lining engineering measures can be considered comprehensively,when the water saving level is high.