Impact Monitoring Of Water Diversion And Impoundment In Danjiangkou Reservoir Based On Time-series Remote Sensing Data

China launched South-to-North Water Transfer Project(SNWTP)in 2002.There is no doubt that the huge inter-basin water transfer project can alleviate water shortages in North China,improve ecological environment of the water-scarce areas such as Beijing City and Tianjin City,and has significant impacts on the economic prosperity in China.But for water diverted area,the water impounded and diverted activities and the resultant land cover changes(e.g.water area change)will surely have complex and profound influences on the regional ecological environment,hydrological process local climate,and Land Cover,etc.Therefore,the SNWTP effects on the water diverted region got focused by lots of researches before and after the Middle Route of SNWDP firstly transferred water.Danjiangkau Reservoir is headwater source of the SNWDP's Middle Route Project.It's on December 12,2014 that the project began to transfer water from Danjiangkou reservoir for the first time.In order to explore effects of initial running of SNWDP's Middle Route on the headwater-source area,this paper firstly studied on identification of the regional various types of land cover and extracted characteristics of spatio-temporal change of typical land cover classes based on remote sensing data and real-time monitoring data of water level elevation before and after Dec 12,2014.Then risk of agricultural non-point source pollution were researched in the submerged area around Danjiangkou Reservoir.The result shows that:(1)Based on color clustering-oriented data fusion of NDWI,MNDWI and NDVI images and application of method of mathematical morphology in image enhancement processing,differences among water cover,building land and sparse vegetation land were enlarged.By using color clustering based remote sensing image classification,various types of land cover were identified With Kappa coefficient higher than 80%.(2)Spatio-temporal change of the regional water cover was obvious because of the running of south-to-north water transfer project.Although acreage of the water cover in Danjiangkou Reservoir had been generally accounting for about 76%of the total area of water cover in the study area and still kept the same obvious inner-changing characteristics of decreasing from December to the following March and rising from March to December since 1987,the peak-acreage of water cover in the Danjiangkou Reservoir occurred on Dec.7,2014.Moreover,the real-time acreage of water cover in Danjiangkou Reservoir was larger at most of the time after running of the Middle Route of South-to-North Water Transfer Project.(3)After the water diversion and impoundment in Danjiangkou reservoir because of the SNWTP Middle Route Project,there.was the obvious land cover change which was characteristic of the reduction of cultivated land and the enhancement of building land.The reduction of cultivated land mainly occurs in riparian zone of the reservoir and hillslope in the mountainous area.And most of the decreased cultivated land located in Xichuan County.Acreage of building land in the study area was giant larger in 2016 than 2010 and new building lands mostly appeared in the central area of Shiyan City.Forest-grass mixed land increased slightly,which mainly resulted from conversion of hillslope cultivated land.(4)After running of the Middle Route of South-to-North Water Transfer Project on Dec.12,2014,acreage of the riparian zone of Danjiangkou Reservoir was larger,and almost half of the riparian zone located in xichuan County.When water level of the Danjiangkou Reservoir changed,acreage decrease of the riparian zone in Xichuan County was also the most significant.Moreover,submerged land cover in the riparian zone mainly consisted of shoaly land,abandoned cultivated land and forest-grass mixed land.Compared with the other submerged land cover,acreage of the abandoned cultivated land was not big,but a lot of used agricultural non-point source pollutants remained in its soil.In addition,there was visible crops planted in the riparian zone of Danjiangkou Reservoir such as corn,peanuts and sesame,which resulted in the continuous use of agricultural non-point source pollutants such as chemical fertilizers,pesticides and herbicides.In the soil of these crop land,samples with higher content of Total Nitrogen(TN)accounted for 10.2%and Total Phosphorus(TP)20.3%.All of these increased risk of agricultural non-point pollution to Danjiangkou Reservoir.