| The Three Gorges Project which is the largest hydraulic engineering in the world,brought many advantages and disadvantages to ecology and environment, so it becomes ahotspot and a point of friction both here and abroad since the project constructed. With thecommissioning of the Three Gorges Project, the relationship between the Dongting Lake andrivers was far more complex in the middle and lower reaches of the Yangtze River. Therewere a large number of scientific problems including hydrology, sediment, ecological andenvironmental aspects, which needed to be studied further. Although in recent years at homeand abroad on the influence of the Three Gorges Project on water level and water surface areaof the Dongting Lake also, the representative was not very adequate because of the smallsample size and the accuracy needed to be improved in the statistical analysis of water leveland surface area. Hence, the Three Gorges Project construction and climate change and otherfactors and combined the quantitative relationship between the variation in the Donting Lakearea and the change of water level remained to be further studied.Therefore, long-term effects on the construction of the Three Gorges Project produced onthe upstream runoff and sediment, the downstream river and lake water area had changed. Theeast Dongting Lake, south Dongting Lake and west Dongting Lake were selected to study.Based on the technology of Remote Sensing (RS), Geo-information System (GIS) analysis,geo-statistical analysis and other statistical method, the change rule of water level and thesurface area have been analyzed in Dongting Lake under the construction of the Three GorgesProject. This article mainly includes the3contents, and the related research conclusions are asfollows.(1) Compared with the threshold value of single band, the relationship between spectrummethod, ISODATA method and the multi-source information method, the results showed thatthe multi-source information method had the highest precision and it was the most suitable forwater extraction. The ISODATA unsupervised classification and the threshold value of singleband for extracting water information could get a better accuracy by setting the appropriatethreshold, and they can basic extract all water pixel. Using the relationship between spectrummethod (NDWI), it had high sensitivity and could enhance the contrast of the water and otherobject although it was not suit for extracting water information in the study area. But thismethod had a better effect in correct pixel number by setting the threshold between-0.3~1.(2) Results indicated that the significant negative correlation was found between NDVIand the water level/surface area of lake region under the background of the construction of the Three Gorges Project. Effect of operation in the early stage of Three Gorges Project on theecological environment of Dongting Lake, the lake had not only changed the distributioncharacteristics of annual average NDVI value space, but also had affected the correlationbetween NDVI and water level/surface area to a certain extent.(3) Results showed that the Dongting Lake water surface area decreased in recent years,and had obvious seasonal characteristics of years by analyzing variation characteristics of thesurface area of the Dongting Lake. The Three Gorges Project operation to a certain extent tothe water surface area, mainly in the stage of storage leaded to the dividing-water anddividing-sad ratios in the three bayous reduction caused by the reduction of water surface area.On this basis, study on correlation of Dongting Lake over the surface area and water level ofChenglingji also found that two polynomial fitting can better express the relationship betweenthe two. Research showed that the Three Gorges Project brought more complex influencefactor to the water level and surface water area of Dongting Lake. |
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