Analysis And Research On Sediment Mud Particles In The Rainwater Outlet In Downtown Area Of Beijing

Nowadays,the utilization rate of rainwater resources in cities is relatively low,and the problem of environmental pollution of water resources is particularly serious.Urban water logging occurs frequently.Therefore a series of researches have been carried out on the construction of "Sponge City" in China and conducted pilot projects in cities such as Beijing.The core of the implementation of "Sponge City" is the drainage infrastructure that implements the operation process of rainwater infiltration,storage,drainage,purification,and release;Rainwater will be discharged into the urban water system after the initial overflow and purification,so the urban water system is the critical key to water drainage and the source of sponge city,as well as the connected skeleton of it;the rainwater and sewage drainage system is the foundation and key method to realize the sponge city.The rainwater outlet is the basis of urban drainage facilities and the establishment of a rainwater and sewage system.It is a necessary condition for the infiltration,storage,drainage,purification,and release of rainwater,and also a link to connect the urban water system.In the process of rainfall,sediment and other objects will be deposited in the sediment to form sewage sludge.The sediment in the rainwater sludge reflects the condition of rainwater catchment,which is helpful to determine whether the area is prone to water accumulation,whether the drainage system is normal or not,and the degree of pollution that overflows into the water system.In this paper,we investigated the Beijing urban area(inside the fourth ring road)and obtained the sediment samples for the the particle fraction experiment.The sampling and investigation follow the principles of repressing and generality.The survey records the latitude and longitude,number,description of the sample,the elevation of the site,and the description of the surrounding environment of the sample point.The survey route is divided into three phases,which are along the third and fourth ring roads:four lines across the urban area and the four representative areas(along the Lotus River,Zhong guancun business district,Anwanli residential area,Ritan Park).A total of 195 sites were set up and 159 actual samples were collected.The particle fraction experiment adopts the sieve analysis method combined with the hydrometer method to obtain the particle grading distribution,draw the particle gradation curve,find the non-uniformity coefficients,and classify according to the US soil classification standard.The study found that the degree of gradation of sediment particles is related to the surroundings of the rainwater outlet,that is,the environment determines the formation of sewage sludge.Combined with the situation at the time of the investigation,it is concluded that the better environment and road conditions,and the areas with low human influence factors are mostly loam soils;on the contrary,they are mostly sandy soils and sandy loam soils;The areas with lower elevation have more sewage sludge,and the areas with more human influence,such as the commercial and residential areas,have more sewage sludge and more large particles,mostly belonging to the sandy soil category.The sedimentation gradation of adjacent rainwater outlets is similar because of the same formation environment.Aiming at the conclusions obtained and combining with the "Sponge City" theory,some feasible suggestions are put forward.Including: the reconstruction of the rainwater and sewage diversion drainage system in Beijing,that is the proposal to set up the initial rainwater treatment device,the connection of the Beijing's urban water system and the construction of reasonable planning.