| After the treatment in Jinghai District,the urban malodorous-black water has been eliminated,but one year later the monitoring results show that the water quality has rebounded.After the investigation,the pollution sources of the Qianjin Canal are overflow in the dry season,replenishment by unconventional water source,sediment pollution,dry and wet deposition load,surface runoff load,garbage on the shore for temporary,uncleaned plants and algae,floating objects and suspended solids,etc...Under the long-term monitoring of the indicators of each cross-section,and analysis of the source of pollution,the impact weight of each main pollution source on the quality of the Qianjin Canal is obtained.And the overflow pollution is the main one of all pollution sources,which has the worst impact on water quality.The single factor index method,the comprehensive pollution index method and fuzzy evaluation method were introduced to evaluate the water quality of the Qianjin Canal.The results show that the water in the Qianjin Canal has been eliminated black and malodor.The current water quality is Class V and Inferior Class V.On the basis of water quality evaluation,the main pollutants and main pollution sources of the Qianjin Canal were obtained,which paved the way for the extraction of the main simulation object and the construction of the pollution source location pattern for the subsequent model.In order to predict the impact of different pollution source reduction measures on water quality,a model simulation study was carried out.Based on the results of various types of hydraulic structures and topographic surveys in the Qianjin Canal,MIKE11 software was used to analyze the entire water flow status and the diffusion of pollutant transfer in the Qianjin Canal.The data of the monitoring sections was introduced into MIKE to set up a model that can simulate the water quality of the Qianjin Canal.And the coefficients,the initial water level and the roughness,are determined respectively as 1.5 meters and 0.033(expressed as Manning coefficient).After all the initial values of the monitored indexes of the Qianjin Canal were imported,the verification results are respectively tested by relative error method,root mean square error method and average absolute error method.The results show that the simulation relative error of the model is within the allowable range,and it can be seen that the simulation of phosphate is more accurate?The simulated results are in good agreement with the measured values,so the simulated results can be used to characterize the measured values.The model can predict the change of water quality with different engineering measures.The simulation results show that when the measure of reducing the discharge volume of the overflow is adopted,the water quality as a whole is better,and can meet the highest limit of the Class V in the surface water quality standard;when the water replenishment measure is adopted,the water quality is only improved within 296 meters from the water replenishment point,which means it can hardly improve the overall water quality of the Qianjin Canal,and this indicates that the water replenishment project,whose capability of water quality improvement is only effective during the appearance of pollutant peaks,is not as resultful as reducing the sewage discharge;when the simulation is carried out by reducing the overflow pollution and water replenishment simultaneously,the effect of the latter is not obvious. |
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