Research On Changes Of Boundary River From Ussuri River To Yalu River Based On Remote Sensing

The change in watercourse of boundary river and in island shoreline of the rivermeans the alteration in national territorial area of both countries, and it is closelylinked to territorial sovereignty of both countries. In recent years, natural and humaninfluences have caused bank erosion in some Chinese boundary river areas andconsiderable loss of shoreside areas, which has directly led to the outflow of China’snational territory. The territory is the treasure passed down from our ancestors, andthe change in boundary river will also have an impact on regular work and life of theChinese inhabitants living in the border areas. Therefore, it is of great significance toset about studying the change in boundary river. However, restricted to politicalreasons, it is impossible to conduct the investigation with traditional methods. Asremote sensing is not restricted to ground conditions and features large quantities ofinformation, it can play a significant role in the research into change in boundaryriver. Northeast boundary rivers are mainly composed of Amur River, Ussuri River,Songacha River, Xingkai Lake, Tumen River and Yalu River, of which the TumenRiver and Yalu River, the China-North Korea boundary river, have suffered greatlyfrom erosion change. With the application of remote sensing, the paper conductedsegmentation researches into the change in boundary river in Northeast Ussuri River-Yalu River reaches. The paper divided the whole reaches into three sections,respectively Yalu River section, Tumen River section, and Songacha River-UssuriRiver section. And each section is divided into upstream, midstream and downstream.And meanwhile, analysis was made on factors of influence on boundary river inTumen River and Yalu River.Based on SPOT data between2005and2012, the paper obtained boundary riverinformation via man-machine interaction interpretation, and made segmentationanalysis of the change of boundary river through the alteration in length of boundaryriver, areas, spatiotemporal dynamics, degree of change and other indicators. It explicated the correlativity between the change in boundary river and climate,topography as well as human activities. What’s more, the paper used partial leastsquares regression model to verify the important role that various factors had playedin the change in boundary rivers within Yalu River areas and Tumen River areas.The research has drawn the following conclusions:1. Changes in boundary riversThe change in Yalu River is mainly reflected in erosion. Upstream andmidstream suffers more erosion than silting, and downstream suffers more siltingthan erosion. Midstream suffers most from the erosion, and downstream suffers mostfrom the silting.Silting dominates the overall change in Tumen River. The siltation within thisarea is more serious than erosion. The midstream suffers most from the erosion, andthe downstream suffers most from the silting.The change in Songacha River-Ussuri River reaches is mainly silting. Thedegree of silting within the entire areas is greater than that of erosion. And thedownstream suffers most from both erosion and silting.2. Topographical factorsYalu River areas feature relatively big difference in elevation. Northeast regionsdwarf the southwest ones. The elevation gradually declines in the flow direction ofrivers. Changbai Mountain areas feature the highest altitude, with the elevation of2,745m. And Dandong estuary has the lowest altitude. The change in boundaryrivers mainly takes place within the altitude of200m. With the rise in altitude, thechange in both erosion and silting has gradually become unobvious. As midstreamfeatures the greatest slope, it suffers most from erosion. Riverbed vertical slope ofboth upstream and midstream is much greater than that of the downstream.Tumen River areas feature relatively big difference in elevation, with thewestern regions towering above the eastern ones. The elevation gradually declines inthe flow direction of rivers. The highest altitude lies near Shiyishui River ofChangbai Mountain, with the elevation of1,550m. And Hunchun estuary has thelowest altitude. The change in boundary rivers mainly takes place within the altitudeof100m. With the increase in altitude, the overall trend in change of erosion andsilting gradually goes down. The upstream features the greatest slope, followed bymidstream, with downstream ranking the third. Riverbed vertical slope fallssuccessively from upstream to midstream and downstream.Songacha River-Ussuri River areas are relatively flat in terrain, with the central areas towering above both sides. Along both sides of the watercourse within RaoheCounty are low mountains and hills. Most river reaches of Ussuri River andSongacha River runs through low and flat plains, low-lying areas and marshwetlands. On the whole, there is not big fluctuation in relative relief of rivers, lesssensitive to the effect of topographical factors.3. Climatic factorsGenerally speaking, the mean annual precipitation in Yalu River areas isslightly on the rise, gradually increasing from the upstream to the downstreamneighboring Dandong City. And it gradually falls from Dandong City to the estuary.In general, the mean annual temperature is on the fluctuating rise, significantlydistributed in three-section pattern. The upstream features the highest temperature,while the downstream the lowest.All in all, the mean annual precipitation in Tumen River areas is slightly on therise. It falls first, then rises, and falls again from upstream to downstream. HuiningCity sees the smallest amount of precipitation. The mean annual temperature risesfirst, then falls, and rises again from upstream to downstream.On the whole, the mean annual precipitation in Songacha River-Ussuri Riverareas is slightly on the decline. It falls first and then rises from Songacha River to thedownstream of Ussuri River. The mean annual temperature is generally on thefluctuating rise, and gradually declines from Songacha River to the downstream ofUssuri River.4. Autologous factors of boundary riversUpstream riverbed of Yalu River features the greatest engineering geologystrength, followed by the midstream, with the downstream the smallest. Thesinuosity ratio of watercourse gradually becomes small in flow direction of the river,and it’s the same with the depth of the river.Upstream riverbed of Tumen River features the greatest engineering geologystrength, followed by the midstream, with the downstream the smallest. Thesinuosity ratio of watercourse gradually lessens in flow direction of the river, and it’sthe same with the depth of the river.On the whole, the Songacha River–Ussuri River reaches are quite weak inriverbed engineering geological strength. Watercourse of Songacha River isextremely winding and frequently wiggling. Straight and microbend reaches ofUssuri River amount to74km, while winding and microbend reaches come to67km. 5. Anthropogenic factorsThere are altogether63Chinese revetments in Yalu River, but the revetments incertain areas have remained unrepaired for years. Shuifeng Hydropower Station,Yunfeng Hydropower Station, Taipingwan Hydropower Station, LaohushaoHydropower Station and other hydropower stations are successively built alongthe main stream of Yalu River. They regulate the annual distribution of water andsediment within the entire main stream of Yalu River. During flood seasons, theincoming flow is reduced, impairing the sediment transport competence of YaluRiver during these seasons. During the dry seasons, the runoff volume increases,giving rise to seasonal deposition in the watercourse during freezing period. Bothsides of the midstream and downstream of Yalu River are natural wetlands, some ofwhich have been irrationally exploited to be arable lands and residential lands. Thesepractices have doubled the risks of water and soil erosion as well as bank collapse.There are totally40revetments under the charge of China in Tumen River.These revetments are basically in good condition, and effective in protecting theriverbank from erosion. Many forest lands in the middle and upper reaches of TumenRiver have been exploited to be dry farmlands. And many wetlands in thedownstream areas have been destroyed and replaced by arable lands and buildings.The change in land use structure has increased the risks of water and soil loss.There are altogether53revetments in Songacha River–Ussuri River reaches,with the majority in good condition. They can properly protect the riverbank fromerosion. However, many wetlands and forest lands along the riverbank of SongachaRiver–Ussuri River have been exploited to be arable lands, a reduction in the sort ofland as highly effective in soil and water conservation as forest land and wetland.The rise in degree of fragmentation is mainly to blame for the increasingly serioussoil and water losses in Songacha River–Ussuri River reaches.6. Influence factor analysisAccording to analysis made with the help of partial least squares regressionmodel, the paper has concluded that slope has the most significant effect on erosionchange in boundary rivers in Yalu River areas between2005and2012. The greaterthe slope is, the more serious the erosion becomes. In addition, the quantity ofprecipitation also plays a part. The rise in the quantity of precipitation will also leadto intensified erosion.Slope and vertical gradient are two factors with the most significant effect onchanges in silting. And both of them are in negative correlation with changes in silting. The smaller the slope and vertical gradient are, the more obvious siltingbecomes. Slope has the most significant effect on erosion changes in boundary riversin Tumen River areas between2005and2012. The greater the slope is, the strongerthe erosion becomes. Besides, temperature also makes a contribution. Temperature isin negative correlation with erosion changes, which shows the reduction intemperature will lead to intensified erosion. Slope and temperature have the mostsignificant effect on changes of silting. Slope is in negative correlation with changesin silting. The smaller the slope becomes, the more obvious the silting will be.Temperature is in positive correlation with changes in silting, which shows the risein temperature will lead to increase in silting.The degree of change in winding watercourse is more significant than that instraight watercourse, and the degree of change in soil shoreline is more obvious thanthat in rocky shoreline. Riparian environment is also influential to the degree ofchange in watercourse.