The Analysis Of The Change Of Water Area In Reservoir Area Based On The Remote Sensing Image Of The Three Gorges Dam

The three Gorges dam is the world's largest hydroelectric project.In June 2003,the dam officially began to hold water,forming a narrow and long,narrow band of river-type reservoir stretching up to 600 kilometers upriver.Among them,the change of water level?135m,156m,and 175m?in upstream of the dam,and the annual operation schedule of the three gorges reservoir.June to September?145m?,the end of October?175m?,11^December?170¹75m?,1^April?when the water supply is in period,the water level gradually drops?,and at the end of May?the flood control limit is 145m?.This has made significant changes in the area of upstream waters.At present,there are some limitations on the relationship between the area change of upstream water area and the pre-dam water level.Therefore,the quantitative analysis of the area of the water area of the upper Jiangjin River in the upper reaches of the dam can provide a theoretical basis for the regional flood prediction mechanism and land use planning.Based on the data of Landsat remote sensing images and the pre-dam water level in 2000²016,this paper takes the example of the riverfront of Jiangjin river in Chongqing before the dam.Firstly,image preprocessing was carried out in Arc GIS and ENVI software,and the water area and contour of water were extracted by MNDWI water index method.Second,according to historical hydrological records in the study area,the extraction of remote sensing image on August 14,2013,results identified as the study area biggest?waters?template,and the maximum cutting template for the rest of the year of the water area in the study area.Thirdly,according to the terrain,the study waters?from the front of the dam to the upstream?is divided into 5 major segments and 11 sub-sections,and the water area changes quantitatively analyzed in the subsection.Finally,by establishing the function relation between the pre-dam water level and the area of each section of water,it provides a realistic basis for calculating the area of the study area.The results show that:?1?The largest template identified through this study?remote sensing image water area of 14 August 2013?:Each channel section is divided into a range of0.28km²⁴.87 km²,and the maximum is in section one.According to this range,it's clear that the farther the distance from the dam,the smaller the area of the water in the subsection of the river.?2?Extract water body information in the largest template and process it in sections:The area of the water area before and after the construction of the dam has changed a lot.The average water area of the dam before the construction is 502km²,and the average water area of the dam after the construction is 639km²,which has increased the average water area of the upper reaches of the dam by 137km² in 13years.At the same time,the change trend of the water area after the water storage has the necessary connection with the three gorges dam.?3?The relationship between the water level in front of the dam?upstream?and the water area of the subsection of the river is established.After the dam building,the area of water area(S _max=502.16 km²),which is adjacent to the dam,increases significantly.The change of area of water area in the area of area 1⁶ of the study area is relatively large,and its variation range is 6.15km²⁶0.84 km²,which is greatly affected by the change of water level.The rest of the river was not significantly changed.Therefore,in this paper,the model of water level and area is established by using the relevant expressions in sections 1⁶.?4?The area of water in the rest of this paper is estimated by the data of the front of the dam?upstream?,and compared with the extracted data from remote sensing images.The results showed that the maximum difference was 20km² on August 22,2016.The smallest difference was on August 25,2009,with a value of4km².At the same time,the total value of the change is between 0.8%and 4.2%.Moreover,the model has the smallest accuracy and error in the study area.?5?This model is used to invert the changes of the water area of each period?dry water,water and abundant water?and analyze the characteristics of seasonal and inter-annual variation.The water level in the front of the dam rises by 0.01mile and the area of the first section increases by 0.0095 km².The area of the water area after the construction of the dam has obviously changed in three phases,and the initial seasonal change of water storage is not obvious.The 2³ stage of water storage?high-value zone?and the period of abundant water?low-value zone?change alternately.The empirical evidence conforms to the water level operation rule of the three gorges reservoir every year.