Construction Of Farmland Utilization System For Desilting And Mud Sewage In Small Rivers In South China

At present,the rapid development of the social economy,the increase in the population base and the gradual improvement of the level of urbanization,the people pay more attention to the quality of water resources.However,due to various natural factors and human factors,the river channel has long-term acceptance of soil erosion in the farmland and surrounding environment and plant spoilage,and the silt is rich in various nutrients,heavy metals and other harmful substances,with the increase of siltation.The accumulation of pollutants has made the river water pollution increasingly serious,which not only seriously affects the river's normal function,but also makes the already scarce clean water resources more searce;therefore,improving water quality,restoring river ecosystems,and reducing pollution sources are ecological environmental protection.The fundamental requirement is to carry out river channel pollution control.In view of the characteristics of small rivers in the south,this paper proposes a system for dredging and muddy sewage farmland suitable for small rivers in the south,which mainly consists of funnel-shaped suction and suction pipes,sewage pipes,sewage pools,inlet pools and small electric irrigation stations.The composition of the water outlet,the channel,etc.,form a complete system of sewage dredging,transportation and utilization.The system is fixedly arranged in the river channel,and can regularly clean the flocculent sediments at the bottom of the river channel,and the sucked flocculent sediments are diluted with the water flow and then input into the farmland by the water pump,thereby simultaneously purifying the river water,beautifying the environment,and Conveying organic fertilizers for farmland to provide nutrients for the growth of crops.The purpose of this study is to change the current method of draining dredging or sucking(digging)mud boat dredging,which is laborious,time-consuming,and affecting the environment and ecology.It can also avoid the situation where it is difficult to store and use the cleared sludge.The main research contents and analysis results of this thesis are as follows:(1)Based on the analysis of sedimentation characteristics of small rivers in South China,Hakanson potential ecological risk index method and geological accumulation index method are used to assess the risk of river sedimentation and sedimentation,laying a foundation for river silt clearance and utilization.? Through investigation and analysis in many places,the sedimentation characteristics of small rivers in South China can be divided into flocculent sediment layer,silty sediment layer and solidified sediment layer from top to bottom.The thickness of flocculent sediments generally varies with the variation of river water temperature.In summer,the high temperature sediments float with the water.The flocculent thickness is 8?10 cm and the average bulk density is 1.15 mg/l.In winter,the water temperature decreases the sediment subsidence,and the flocculent thickness is 4?6 cm and the average bulk density is 1.45 mg/l.The thickness of muddy sediment layer increases with the increase of sedimentary years.The average thickness of muddy sediment layer is 20?50 cm,with an average annual deposition of 3-5 cm and an average bulk density of 1.9 mg/l.The bottom of solidified sediment is the bottom sediment,which is formed by decades of sedimentary superimposition,with an average bulk density of 2.5 mg/l.?The risk assessment of river siltation is mainly aimed at the assessment of more than 10 harmful heavy metal sediments.Hakanson potential ecological risk index method is used to determine whether the concentration of major heavy metal pollutants will pose risks to field crops.Without risk,organic fertilizer water can be directly transported to the field through silt removal and farmland utilization system;if there are risks,chemical transfer is necessary.Chemical method,bioleaching method and phytoremediation method can reduce the concentration of heavy metals.?In order to accurately collect sediment and water quality in small rivers,a new type of sediment and water sample collector has been developed in this paper,which can conveniently control the collection of surface,middle and bottom sediments of the whole water layer and bottom sediments,and realize the accurate collection of physical and chemical properties of each layer of sediments.(2)The dredging effect analysis and optimization design of the constructed small river channel dredging and mud sewage farmland utilization system in the south.In this paper,the theoretical method of three-dimensional turbulent computational fluid dynamics is introduced.The three-dimensional flow numerical simulation of the mathematical model of the water flow near the suction inlet at the bottom of the river channel is carried out for different design schemes.The governing equations are Reynolds mean Navier-Stokes equations(RANS)and standard equations,solved by SIMPLEC algorithm tinder given boundary conditions.Through the example analysis,the numerical simulation of the six sets of design schemes is carried out.The three indicators of the flow pattern of the suction system at the bottom of the river dredging system,the uniformity of the cross-section velocity distribution and the cross-section water flow are considered as follows.Scheme 6(B1=5m,N=1)is the optimal solution.It provides a scientific basis for the design practice of the system in the future.