Research On Impact Of Cascade Reservoirs And Water Diversion On Water Environment In The Middle And Lower Reaches Of The Hanjiang River

Promoting high-quality development of the Yangtze River Economic Belt is a major strategic decision of the country in the new period.The middle and lower reaches of the Han River occupy an important position in the Yangtze River Economic Belt.The development and utilization of water resources in the middle and lower reaches of the Han River has changed the ecological environment and hydrological situation of the river basin.Under the new situation,combined with the national strategic needs,the implementation of precise and refined environmental management and control of the basin,and the study of the impact of the development and utilization of water resources on the middle and lower reaches of the Hanjiang River on the water environment are of great significance to the realization of coordinated and sustainable development of the basin.This paper combines the national main function strategy and space management and control requirements,and adopts a water environment mathematical model to study the impact of water transfer and cascade development on the water environment in the middle and lower reaches of the Hanjiang River.The main results achieved are as follows:(1)Summarized the domestic and foreign research results of the environmental impact of water transfer and cascade development.At present,the research on the impact of water resources development on the water environment mainly focuses on changes in the hydrological situation and the support for regional development.The mathematical model is to develop water resources.The development of environmental impact research is a mature and effective tool,and the impact of the development and utilization of water resources in the middle and lower reaches of the Hanjiang River on regional development needs to be further studied under the demand for modernization of environmental governance capabilities in the new era.(2)Considering the engineering measures of water resources development and utilization in the middle and lower reaches of the Han River and the characteristics of non-point source pollution,the USLE soil erosion equation and the one-dimensional hydrodynamic water quality model are coupled to establish a numerical model of the water environment in the middle and lower reaches of the Han River.The model parameters were verified using the measured data of typical sections from 2015 to 2016.The error between the simulated value of the water level and the measured value is less than 0.1m,and the error between the simulated value of the water quality and the measured value is less than 15%,which meets the accuracy requirements of simulation research;on this basis In conjunction with the positioning of the main functional areas of the county,with the goal of comprehensively improving the quality of the water environment,a water environment capacity model for the lower reaches of the Hanjiang River for water transfer and cascade development was established.(3)The water diversion of the middle route of the South-to-North Water Diversion Project,the cascade hub,and the implementation of the Han-Ji-Wei project will all deteriorate the main stream water quality to a certain extent.Increased by 21.28% ～40%,TP concentration increased by 31.25% ～ 46.67%.(4)Both water transfer and cascade development will reduce the water environment capacity of the middle and lower reaches of the Han River to varying degrees.After the implementation of the South-to-North Water Diversion Project,the NH3-N water environment capacity decreased by 18.2%,17.1%,and 2.1% respectively,and the TP environment capacity decreased by 32.3%,19.4%,and 4.7%,respectively.Water engineering has the most significant impact on the water environment capacity of the middle and lower reaches of the Han River.(5)The water environment capacity of the districts(counties)in the middle and lower reaches of the Hanjiang River shows a trend of increasing from northwest to southeast and from upstream to downstream.Combined with the main functional positioning of each district(county),the water environment capacity of key development zones,main agricultural product producing areas and key ecological function zones accounted for 69.3%,27.2% and 3.50% of the whole region respectively.The development needs of the district,and effectively protect the ecological maintenance functions of key ecological zones,provide support for the strategic environmental management of the main functional zones.