Study On Water Quality Evaluation And Risk Assessment Of Changsha Section Of Xiangjiang River

With the occurrence of emergencies such as the water environment and related issues,it is particularly important to grasp the water quality of rivers and lakes and to conduct risk assessments.Taking the Changsha section of Xiangjiang River as the study area,combined with the 2016Landsat-7 and Landsat-8 satellite image data,and the measured data of water quality of total phosphorus,dissolved oxygen,permanganate index,ammonia nitrogen and five-day biochemical oxygen demand,The water quality status was evaluated by four evaluation methods:factor evaluation method,comprehensive evaluation method,traditional Nemero index method and improved Nemero index method.The risk assessment of the study area is carried out through the combination of Remote Sensing?RS?and Geographic Information System?GIS?technology and risk assessment techniques.The results are mainly as follows:?1?The evaluation results of the four water quality assessment methods show that the water quality of the Changsha section of the Xiangjiang River is in good condition,and the seven monitoring sections basically meet the Class III water centralized drinking water standards in the surface water environmental quality standard?GB3838–2002?,and the evaluation results The medium water quality category is dominated by I-II water.?2?In the four methods of single-band threshold method,multi-band spectral relationship method,normalized difference water body index method and improved normalized difference water body index method extracted from water boundary,the normalized difference water body index method is the most ideal.The accuracy rate is 97%.?3?Among the water quality distribution data obtained by remote sensing technology inversion,the water concentration values of TP,DO,COD_Mn,NH₃-N and BOD₅ in the Changsha section of Xiangjiang River are basically between the I-III water in the surface water environmental quality standard.On the whole,the concentration of some water quality indicators in the lower reaches of the Changsha section of the Xiangjiang River and the Liuyang River and the Laodao River are relatively high.?4?In the risk assessment grading data of Xiangjiang Changsha section,the areas occupied by high-risk area,higher-risk area,medium-risk area,lower-risk area and low-risk area are 4.32,9.24,25.91,14.29 and 2.74 km²,respectively.The areas where the risk sources on both sides of the Changsha section of the Xiangjiang River are concentrated are the main distribution areas of the high-risk areas.The higher-risk areas are mainly distributed in the bridges of drinking water source areas and the areas where the risk sources on both sides of the Changsha section of the Xiangjiang River are sparse,medium-risk areas.The bridges are mainly distributed in the transition zone,drinking water source zone and landscape entertainment water zone and the upper and lower parts of the Changsha section of the Xiangjiang River.The low-risk zone and the lower-risk zone are mainly distributed in the middle and lower reaches of the Changsha section of the Xiangjiang River.