Analysis And Study On Water Environment Characteristics Of Canal

As the lifeline of transportation and irrigation in China,the Beijing-Hangzhou Canal is not only the main channel of the eastern route of the South-to-North Water transfer Project,but also a cultural corridor to communicate with many important regions.As an important polluted water body,with the establishment of the key construction area of the Grand Canal National Culture Park in the Jiangsu section of the Grand Canal,the ecological environment quality around the Grand Canal has been paid more and more attention in recent years,and the improvement of the canal water environment has been carried out gradually.Therefore,it is necessary to analyze and study the characteristics of the water environment in the canal area,so as to provide reference and basis for the improvement of water environment quality in the basin.This paper takes the full-length 23.9km reach of Wujiang section of Beijing-Hangzhou Canal（Guajingkou North-Taipu River）as the research object.Firstly,the regional pollution load is estimated from three aspects:domestic pollution,industrial pollution and surface runoff.The main pollution factors are selected based on principal component analysis（PCA）.The water quality from 2018 to 2020 is evaluated by single index and Nemero index,and the evaluation results are tested by discriminant analysis.The results show that the domestic pollution load in the study area is relatively high;ammonia nitrogen,total phosphorus,total nitrogen,COD,BOD5 and permanganate index are the main pollution factors;the accuracy of discriminant analysis is 84.7%,and the water quality is improving year by year,but light pollution will still occur in some sections.Secondly,the canal water environment model is constructed based on MIKE 21,and the temporal and spatial variation characteristics of water environment are analyzed from two aspects of hydrodynamics（water level,wave,velocity）and water quality（six main pollution factors）.The simulation results show that the water level,wave disturbance amplitude and velocity show the characteristics of high in summer and low in winter;the water level decreases gradually from north to south,and the wave disturbance amplitude and velocity are relatively high in the south of Wutongqiao;the concentration of pollutants decreases gradually from upstream to downstream,and the water quality of COD,total phosphorus,permanganate index and BOD5 is good（III）.The nitrogen index was poor,and the total nitrogen concentration reached 2.3mg/L in the first two quarters,and was easily affected by upstream concentration accumulation.Generally speaking,the Wujiang Canal plays a good role in the transition of water quality,and the concentration of pollutants from the upper reaches has a relatively great impact on the water quality of the canal research section.Furthermore,the main river and tributaries are used to generalize the sewage outlet to the model,and the temporal and spatial variation of water quality under the influence of sewage outlet is analyzed.The results show that the influence of D02～D04 outlet on ammonia nitrogen of canal is greater than that of D01 outlet,and the ammonia nitrogen in water can be reduced from III to IV.The influence of each sewage outlet on the total phosphorus of the canal is relatively weak,and the water concentration is basically kept within the 0.16mg/L.With the increase of flow rate,the arrival time of the pollution front to the canal appears in advance in varying degrees,and at the same time,the concentration of the pollution front entering the canal is increased to some extent.Aiming at the sudden oil spill accident,the oil spill model is established,the migration and diffusion process of oil pollution is analyzed,and the reference indexes are listed.The results show that when a total of 5 tons of fuel oil is leaked for 1 hour,the diffusion and degradation rate of petroleum pollutants in Sanliqiao-Wu Tongqiao is faster,and the degradation rate slows down when it reaches Wutong Bridge.The arrival time,residence time,peak concentration and peak time of the oil film front are negatively correlated with the flow rate.Finally,based on the simulation results of water environment,the water environmental capacity and residual environmental capacity of the canal are calculated,and the proportional statistical method is used to qualitatively analyze the residual pollution carrying capacity of the water body.According to the IV standard,the canal has more water environmental capacity and residual environmental capacity,and the water body still has a certain pollution-carrying capacity.Under the III standard,the proportion of residual environmental capacity of COD and NH₃-N is generally low,and shows the characteristics of flat water period<high water period<low water period;the proportion of total phosphorus residual environmental capacity is relatively large,and the overall pollution carrying capacity is still about 30%.