Water Quality Evaluation Of Nandu River Based On Cloud Model And Support Vector Machine

China is a country with extremely uneven distribution of water resources,showing a trend of more in the south and less in the north.Hainan Island,as the southernmost province in China,is characterized by abundant water resources and good water quality,which is rare in China.However,in recent years,with the rapid economic and social development and the increasing population of Hainan Island,the quality of water resources has become increasingly prominent.As the main surface water source of Hainan Island,the assessment of water environment quality of Nandu River is conducive to understanding and mastering the present situation and changing trend of water quality of Nandu River,and providing safety guarantee for the development and utilization of water resources and the construction of ecological circle in Hainan Island.Because of the characteristics of water environment system and some common problems of traditional water quality evaluation methods,such as low prediction accuracy,relatively narrow scope of application,and ignoring the randomness and ambiguity of influencing factors,many scholars began to explore new evaluation methods for water quality evaluation.In this paper,cloud model and support vector machine（SVM）are combined,and"SVM cloud model comprehensive evaluation method"is adopted to evaluate the water quality of Nandu River,which provides an objective and easy-to-operate water quality evaluation method for water resources development and ecological circle construction in Hainan Island.Based on the investigation of water quantity and water quality of Nandu River in Hainan Island,combined with cloud model and support vector machine theory.According to the actual monitoring situation and pollution characteristics of five national control sections of Nandu River in four seasons of 2020 and six years from 2015 to 2020,the SVM cloud model comprehensive evaluation method was adopted,and seven indexes of p H,dissolved oxygen（DO）,permanganate index(COD_Mn),chemical oxygen demand（COD）,ammonia nitrogen,total nitrogen and total phosphorus were taken as water quality evaluation parameters.The water quality of Nandu River sections were comprehensively evaluated,and the results were compared with the results of matter-element analysis.The research contents and results are as follows:（1）The cloud model comprehensive evaluation method comprehensively considers the interaction of seven water quality indexes,and avoids one-sided evaluation of water bodies.The collected seven water quality indexes are normalized and PCA treated,and the best parameters C and G are determined by cross-validation,and the final evaluation results are obtained.This evaluation process is a comprehensive evaluation of water quality indexes,and machine learning results are added,so the obtained water quality evaluation model reflects the comprehensive results of seven water quality indexes.（2）In the comprehensive evaluation of water quality of Nandu River,the evaluation results of matter-element analysis and SVM cloud model comprehensive evaluation have high credibility and objectivity.However,the calculation formula of matter-element analysis method is complex and the amount of calculation is large in practical application.With the increase of monitoring data,the possibility of errors in evaluation results will also increase.By comparing the basic theory with the actual calculation process,the SVM cloud model comprehensive evaluation method is superior to the matter-element analysis method in both theory and practical application,and its operability is stronger and its calculation accuracy is higher.It can be considered that SVM cloud model comprehensive evaluation method is feasible and applicable in the comprehensive evaluation of water quality of Nandu River,and it can reflect the water environment status of Nandu River conveniently and quickly.（3）The SVM cloud model comprehensive evaluation method is used to analyze the water quality of various sections of Nandu River from 2015 to 2020.The results show that the water environment quality of Nandu River is in an excellent state in recent years,which is in good agreement with the actual situation and verifies the applicability of the model.The purpose of this paper is to verify that SVM cloud model comprehensive evaluation method can evaluate the water quality of Nandu River,and it can be extended to other rivers in Hainan Island.