Simulation And Effect Evaluation Of Water Environment Treatment Project For Medium And Small Sized Rivers Through The Model MIKE 11

At present,the plan of compensation and the pollution are unmacthed during the water environment treatment of medium and small-sized riverse,resulting in the poor treatment performance and the investment waste.The water quality model,which is a mathematical description of the various substances evolution in the water body,can be used to predict the effectiveness of the treatment projects.MIKE 11 model with the advantages of comprehensive functions and convenient operation,is widely used in watershed management.In additon,water quality models are applied to systematically analyze,simulate and evaluate the river water environment treatment projects,and the mismatch between the treatment projects and the current pollution situation of the river could be effectively solved,which has a good application value.Firstly,this study takes the River A（the third-level tributary of the Yangtze River）as an example,a river water quality model based on MIKE 11 was built.The flow,chemical oxygen demand（COD）,NH₃-N and total phosphorus（TP）were calibrated with the measured data.The average relative error of the simulation results was in the range of3.91%-12.02%.The constructed water quality model well reflected the hydrodynamic and water quality conditions of River A.Secondly,in order to understand the current water environment status of River A,the single-factor evaluation method was used to evaluate the quality of water,based on the collected data and field investigations.The source and contribution of the pollution were analyzed from three aspects:point source pollution,non-point source pollution,and internal source pollution.In addition,with the help of the constructed water quality model,the dynamic water environment capacity of River A was calculated by the model trial and error method.The results show that the quality of River A was inferior to Grade Ⅴ,and NH₃-N and TP were seriously exceeding the standard,the pollutants mainly come from non-point source pollution and sewage treatment plants.The effluent and domestic sewage are directly discharged,while the pollution released by the river bottom sludge was relatively light.The simulation results of the model found show that the water environmental capacity of River A changed during the whole year,especially at high and low water periods.The total amount of pollution entering the river upstream exceeded the water environmental capacity.This situation was more prominent in the dry season.According to calculations,the emission of COD,NH₃-N and TP that need to be reduced were 7.14 t/a,2.38 t/a and 0.48 t/a respectively to meet the water environment capacity requirements.In order to solve the current water environmental problems,four measures were proposed:point source pollution interception,non-point source control,sewage treatment plant upgrading and transformation,and ecological water replenishment.Finally,in order to study the effectiveness of various measures on improving water quality,the MIKE 11 model was used to simulate and predict the treatment effects,the analytic hierarchy process was also used to construct an effective evaluation system for water environmental treatment programs.The results show that ecological water replenishment had the best effect on improving the water quality of the river,followed by the upgrading of sewage treatment plants and the point source pollution interception measures,both of which have the same efficiency.The non-point source control measures have the lowest efficiency,but it can effectively guarantee the water quality of the river during the flood season.Verified by simulation,the comprehensive treatment plan can effectively improve the water environmental quality and the water quality was improved to the surface water level Ⅳ standard.In study,the effects of water environment treatment programs for medium and small-sized rivers were simulated and evaluated through the MIKE 11 model,and provided a certain reference basis and technical support for the water environment remendiation projects.