Research On The Hydraulic Flap Gate And Filter Dam In The Field Ditch For Controlling Water Pollution

In recent years, the excessive use of agricultural fertilizers and pesticides have caused the non-point source pollution which has a serious impact on water quality. The engineering measures can control the agricultural non-point source pollution effectively. The field drainage ditch is excavated for the purpose of the excavation of the water channel. It is the necessary way for the dirt in the field to enter the river. Through constructing the flap gate which can filter water and intercept sewage in the field drainage ditch. It helps intercept the field emission runoff. From using the different filter combinations to retain the farmland of pollutants discharged can help reduce the agricultural non-point source pollution to downstream water hazards. In this paper, the design of the flap gate is divided into two parts in the structure, the upper part is the hydraulic automatic flap gate, the lower part is the filter dam. The main research results of this paper are as follows:1.Elaborating the functions and characteristics of the drainage ditch system in the field, discussing the migration process of nitrogen and phosphorus in the drainage ditch and its effects on nitrogen and phosphorus retention.2.Designing hydraulic automatic flap gate. According to the principle of moment balance, the static and dynamic working principle of hydraulic automatic flap gate are analyzed. According to the basic balance equation of the gate and the force condition of the dynamic process of the gate, it is concluded that the gate shaft is installed at the gate of about 3/10. Based on it, I design the fixed axis type of hydraulic automatic turning plate brake.3.Filter dam structure design and substrate selection. According to the need of the stability of the dam and water permeability, I can determine the dam structure:the middle is filler substrate, on both sides of the grade is gravel filter body, the outside is rockfill. Their particle sizes are determined by the theoretical analysis and the experiments. Based on it, the seepage flow of the filter dam is determined by the comprehensive seepage flow coefficient.4.Different substrate sewage interception test. In filter dams, by replacing the five preselected single substrates to do contrast interception test and drawing the conclusion that it is better for cinder and ceramsite to remove COD、TN and TP, activated carbon and zeolite decontaminate in general, the coarse sand is good at permeability and its guiding water ability is the best. In the mixed substrate interception adsorption test, according to the test results of the single substrate absorption, we can select different combinations of substrates consisting of different proportion of cinder, ceramsite and coarse sand. From determining its decontamination effects respectively, we can draw that cinder, ceramsite and coarse sand remove COD、TN and TP better than other mixed substrates and determine that 2:1:1 ratio of cinder, ceramsite and coarse is the best mixed substrate.