Research On Non-point Source Pollution In The Harbin Section Of The Zhaolan Xin River Basin Based On SWMM Model

Water is the cornerstone of human civilization,and water resources play a pivotal role in human production and life.As a spatial carrier of water resources,the safety of the water environment in a river basin is an important component of national environmental security.It not only provides safe housing for coastal residents,but also brings inexhaustible opportunities for economic development.However,in recent years,the frequent occurrence of water environmental pollution incidents in river basins has caused serious impacts on the lives and health of coastal residents.Since the layout of the "14th Five Year Plan"(2021-2025),the water environment quality of key national river basins has been continuously improved,especially for the control and treatment of urban point source pollution,which has achieved positive results.However,in the process of continuously promoting the improvement of the water environment,as the prevention and control of point source pollution enters the bottleneck period,non point source pollution gradually occupies an important proportion.In response to the above issues,the comprehensive management system for non point source pollution,which aims at scientific analysis,accurate simulation,and plan formulation,has gradually become a research hotspot.In order to scientifically analyze the spatiotemporal distribution characteristics of non point source pollution loads,the use of hydrological and water quality models for numerical simulation analysis of the study area has become a major research tool for non point source pollution.Therefore,this study takes the Harbin section of the Zhaolan Xin River as a typical agricultural watershed research area.Based on ArcGIS and PIE-Engine remote sensing cloud computing service platforms,DEM and high-resolution satellite images are used to establish a basic geographic information database for the research area.On this basis,the establishment of a watershed non point source pollution simulation system was completed using SWMM.Taking the continuity errors of surface runoff routing,river flow routing,and water quality routing as evaluation criteria,it is proved that the SWMM model established in this paper is stable and reliable.Scenario analysis of different rainfall intensities was conducted to simulate the transport of TN and TP with surface runoff within the study area,and the spatiotemporal distribution characteristics of non point source pollution loads were analyzed.The main research results include:(1)Based on the PIE-Engine remote sensing cloud computing platform,a K-Means classifier is constructed to perform unsupervised ground object classification learning using high-resolution 6 high satellite multiband fusion images as training samples.The interpretation results of the underlying surface of the research area are converted into raster data for SWMM modeling.It is verified that the Kappa coefficient of the model is0.75,showing high prediction accuracy;(2)Using ArcGIS to process the DEM data of the study area for filling in depressions,using river channel grid data to secondary correct the DEM data after filling in depressions,using the ArcGIS hydrological analysis module to calculate the flow direction and flow,extracting the river network,and performing river connection and network classification,finally dividing the study area into 151 sub-catchment areas;(3)A spatial geographic element database of the study area,including attribute information of river courses and sub-catchment areas,was established,and the generalization and attribute extraction of hydrological objects were completed using ArcGIS related tools.Further,the rapid establishment of the rainfall runoff model of the study area was completed through the interaction of Access dynamic link library and SWMM input files.Finally,the selection and setting of SWMM related modeling parameters were completed according to the actual situation of the study area.(4)Using the Chicago Rain Pattern Generator to construct multiple return period rainfall events,the spatiotemporal distribution characteristics of pollutant erosion loads in the sub-catchment area were mastered through simulation of short duration and different intensity rainfall scenarios.(5)The combined measures of planting grass ditches and biological retention grids were used to transform the non point source pollution risk plots and corresponding plots on both sides of the main stream in the study area.When the rainfall reappeared for one year,the reduction in the total surface runoff in the study area reached 46.22%,and the total runoff control rate increased by 5.35%.When the rainfall returns to 100 years,the total surface runoff in the study area decreases by 13.80%,and the total runoff control rate increases by 4.24%.(6)The prevention and control measures for non point source pollution proposed in this article can reduce the impact of non point source pollution on the downstream water environment under the rainfall scouring scenario to a certain extent.On the one hand,under the 100-year excessive rainfall scenario,the setting of LID can reduce the scouring load of TN and TP by nearly 15%.On the other hand,under the 100-year excessive rainfall scenario,the setting of LID reduced the peak outflow concentrations of TN and TP at the discharge outlets in the study area by 27.55% and 25.52%,respectively,and the average outflow concentrations of TN and TP decreased by14.73% and 14.71%,respectively.