| The land and resources in boundary river areas are special. The change of river course will not affect the ecological environment along the bank. Besides, it is closely related to the benefits of local people, what’s more, it will affect the change of land area of the two countries, which is related to the territorial sovereignty of two countries. In recent years, some boundary river regions in China are affected by natural and manmade factors, the river course changes subtly, especially in the banks with serious erosion, which may result in the invisible loss of our national land area and harm the interests of our nation and people, the change of river course has exacerbated the instability factors of use of bank land resources, which is harmful for construction of homeland security. The southwestern boundary river areas are located in the front area of “the Belt and the Road” as the key channel to connect countries in Southeast Asia, which plays a significant role in stability and prosperity of the region, The research of river course changes in a part of Yunnan in southwestern boundary river areas can help master the law of change and effectively prevent unnecessary international disputes with great significance for the stability and prosperity of border areas. However, due to the restrictions of politics, human resource and material resources, the traditional method of research is difficult to achieve the goal, with the development of aerospace and aerial survey technology, the application of remote sensing and GIS technology in river changes has become increasingly mature and played a key role in river changes with unparalleled advantages.The research is based on multi-source remote sensing data by means of remote sensing and GIS technology, the information of the boundary river between China and Vietnam Yuanjiang River-Hekou, the boundary river between China and Burma Shweli River-Jiegao as well as the use of land along the river is extracted through the combination of automatic extraction of water and artificial visual interpretation, it studies the law of temporal and spatial dynamic changes through interannual(1989-2014) and annual(2014) changes in order to analyze the differences of temporal and spatial dynamic changes between the two boundary areas, in addition, it explores the influencing factors that cause the differences in boundary river changes and potential impact of boundary river change. The major research contents and results are listed as follows:1. The interannual temporal and spatial dynamic changes of boundary river. According to the research basing on three points of view of river surface, shoreline and interannual changes of sandbank, the temporal and spatial dynamic changes of Hekou and Shweli River have their own characteristics with significant differences.Hekou boundary river area decreases without significant changes of river structure. The coastline change between China and Vietnam presents the fluctuations of decrease and increase, the change in China is greater than that in Vietnam, however, the change degree has become smaller since 2002, the shoreline erosion between China and Vietnam is consistent with decrease of erosion area and increase of sedimentation area, the shoreline erosion in China is more severe, and sedimentation of shoreline has become obvious since 2002, the shoreline change is mainly presented in new area, the change degree becomes greater and displays severe erosion, the erosion shifts from the weak sedimentation to strong sedimentation. The sand area change trends in China and Vietnam are the same, the sand area increases with accelerated pace of change with obvious feature of periodic change, the area of diara and central bar increases to a large extent at a rapid speed, which was very significant especially after 2002, the erosion in China is more severe than that in Vietnam especially after 2002, however, the sedimentation in Vietnam changed obviously, erosion and sedimentation in diara and central bar becomes increasingly obvious with increasingly weak situation of erosion, in addition to the reduction of narrowed area in change of sandbank, the four situations of expansion, newborn, disappearance and the unchangeable increase to different extents, and the expansion grows significantly, the sandbank area increases obviously with strengthened degree of change, the sedimentation degree is obviously larger than erosion degree.Although the Shweli boundary river first increases and then decreases, the overall area decreases obviously, besides, the river structure changes obviously. The phenomenon of curving cut-off is significant, the coastline changes in both China and Burma are inverted, from 1989 to 2001, the boundary river flowed slightly towards China, which increased the length of coastline in China, however, the boundary river flowed towards Burma since 2001, which shortened the length of coastline in China, in the past 20 years, the coastline mainly flowed towards Burma, The coastline change in China was more dramatic than that in Burma, but the degree was weakened since 2001, the erosion and sedimentation in China and Burma are consistent with reduction of erosion area, the sedimentation area increased since 2001, the erosion degree of the coastline in China is more serious, and the sedimentation degree in Burma is more serious, the shoreline change is mainly presented in increase of narrowed and disappeared and decrease of enlarged and new area with intensification of shoreline change degree, the change degree becomes greater and displays severe erosion, the erosion shifts from the weak sedimentation to strong sedimentation. The sand area decreases with slowdown of change efficiency and speed. Especially after 2001, the marginal bank changed little, and the overall area of diara and central bar decreased, but the change degree became more serious since 2001, the erosion, sedimentation and unchangeable area of marginal bank in China and Burma increased, but it was more serious in China than in Vietnam, the sedimentation and unchangeable area of marginal bank in Burma were more serious, the sedimentation in diara and central bar was increasingly severe and the erosion was increasingly weak, in addition to the increase of disappeared area in sandbank change, the four situations of expansion, newborn, disappearance and the unchangeable decrease to different extents, the proportion of disappeared and narrowed area increased obviously, the sandbank area decreased with strengthened degree of changes, the sedimentation degree is obviously larger than erosion degree.Contrast of the two rivers, the river structures in Hekou and Shweli are different with respective features of changes, the changes are strengthened in both the rivers. The degree of change in Shweli is larger than that in Hekou, which is most obvious in changes of sandbank area and erosion and sedimentatation, but the changes in sandbank are not as dramatic as those in Hekou. The periodical features of the two boundary rivers are obvious, especially after 2001(2002), the change degree gap between the two rivers is narrowed gradually, the erosion is great and weak sedimentation area shifts to strong sedimentation area, the trend that sedimentation degree is larger than erosion degree has become increasingly obvious.2. Annual temporal and spatial dynamic change of the boundary river. According to the research basing on four points of view of river surface, shoreline, sandbank and section, the changes in flood and dry season in Shweli are more obvious than those in Hekou, from dry period to flood period, the shorelines in both the boundary rivers are shortened with the decrease of sandbank areas, the changes of the shoreline and flood and dry change of sandbank in China in Hekou are larger, and the changes in neighboring country in Shweli are larger. There is mutual transformation to different extents between the two boundary rivers, diara and central bar, however, the flood and dry changes in diara and central bar in Shweli are larger, and the mutual transformation degree of water and sandbank is much higher than that of Hekou. On the other hand, the flood and dry changes in both the rivers are affected by the basic law that precipitation decreases gradually from the North to the South, the changes of the river are greater in the South than that in the North, the flood and dry changes in bending rivers are more obvious than those in straight rivers, besides, the section changes in flood and dry season are greatly affected by human activities, in general, the changes of water change significantly in places where there are more human activities.3. Influencing factors of changes. From the analysis of the impact of natural and man-made factors on changes of boundary river, boundary river changes are mainly caused by natural factors such as topography, slope, temperature, precipitation and factors of river as well as man-made factors such as land use, bank protection projects and so on. There is negative correlation between altitude and slope and the erosion and sedimentation changes of boundary river, there is positive correlation between large longitudinal riverbed gradient and the erosion and sedimentation changes of boundary river, there is positive correlation between precipitation and river power, besides, there is positive correlation between temperature and quantity of evaporation. The change degree of bending river is larger than that of straight river, which is reflected in the change of land use structure, the development of river bank land is too excessive, resulting in the great changes of water course, bank protection projects play a positive role in protecting the banks.4. Potential impact of changes. The study can explore the potential impact of boundary river changes on homeland security, ecology and navigational conditions. The research of temporal and spatial dynamic changes of boundary rivers can promote construction of homeland security, effectively reflect the impact of ecological changes in boundary rivers and lay a foundation for the changes of navigational conditions.Although the research has made some achievements, it is insufficient in data source, research content and quantitative analysis of influencing factors of changes, which needs to be studied further in the future. |
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