Study On The Pollution Control Of Combined Sewer Overflow For The Old Urban In Beijing Based On Mike Urban Model

The drainage structure in the old urban areas of China is a confluence system,along with the acceleration of urban construction,the urban impervious area in is more and more polluted,and the phenomenon of combined sewer overflow pollution have appeared.This paper is determined by means of drainage pipe network model software Mike urban and technology of auxiliary tools Arcgis,with Beijing longtan lake as an example.Through the research and analysis,this paper finds the most effective solutions to the problem of confluence overflow pollution in the researching area,it provides the basis of reference for transformation on confluence system and control project of overflow pollution in current old urban area in Beijing.The highlight of this article lies in the fact that it is not directly using a measures or plan to carry out the research on the confluence of the overflow pollution control,it is to establish the model of the longtan river basin and arrive at the accurate rate of the overflow pollution control in Beijing according to the requirement about confluence overflow pollution control,namely,the most basic premise of the annual overflow is no more than 4 times.After grasping the current basic situation,the author collects the plan measures for the confluence overflow treatment at home and abroad,proposing the single measures,the comprehensive measures,etc,makes use of the typical annual rainfall data for carrying out the simulative experience with the model of each set of schemes,screening out the most suitable and effective control schemes.In the end,the method is evaluated by the expert in the way of scoring.The researching conclusions of this paper mainly include the following aspects:(1)After comparative analysis can be used to carry out various models of urban drainage network simulation,combining with the current situation of regional pipeline network and data conditions,finally,Mike urban is selected as the model software of this researching topic.(2)Geographic information database of Longtan drainage basin is established,also build the model of drainage pipeline network and the verification accuracy standard runoff coefficient adopted flow fixed rate of the model,the peak flow amount and peak time is allowed to have error only within the range of 15%and 60 min,each parameter finally confirm pipeline manning for 0.0147.the average speed of surface confluence is 0.4m/s;The average time of surface confluence is 5～10min.the runoff coefficient of construction is 0.75;The runoff coefficient of road is 0.8;The runoff coefficient of greenbelt is 0.15.The parameters are all in the requirements of the design specification,proving that the model is correct in the calculation of rainfall runoff and networkhydraulics,and having a scientific guiding role in the selection of drainage model calculation methods.(3)Based on the theory of environmental system analysis,the current situation is investigated,and the comprehensive runoff coefficient of longtan drainage basin is 0.75,and the impervious area is relatively large.The overflow almost happens when rainfall,and the annual flow rate of COD,ammonia nitrogen and TP is 111.01t,3.71t and 0.72t respectively,causing serious pollution to the west lake of longtan.It confirmed the necessity of this research project and the reform of Beijing confluence system.(4)This paper puts forward a variety of schemes based on source,pipeline marking and terminal storage for solving the overflow pollution in longtan river basin,and carries out a series of comparative study.Under the requirement of the most basic premise,it means the annual overflow times of confluence is no more than four times.Furthermore,it lays the foundation for the further construction of sponge city,and it has important practical significance.At the same time,the results coincide with the traditional formula method,which proves that the model is reasonable and helpful to the drainage network model.(5)The expert scoring method is used to evaluate the scheme of overflow pollution control in the selected longtan river basin.the score of ultimate scheme is 88.3 points,having relatively higher one.Recently,it is proved that the solution to the problem of confluence overflow pollution in longtan drainage basin is accepted and accords with the requirements of humanistic suitability.