| The stability and the development trend of channel slope are of great significance to the flood control and navigation safety,the research on this field therefore has always been a hotspot and focus in the study of geoscience.Since the 20 th century,as human society develops progressively,the large-scale water conservancy projects of the Yangtze River basins have great impacts on the dynamic,sedimentary and geomorphic process of the river channels,which have great influence on river bank scouring.In the middle and lower reaches of the Yangtze River,some of the channel slope degrees are increasing and the frequency and intensity of bank collapse increase as well.The stability and security of channel slopes are no doubt being tested.The traditional measurement in channel slope is relatively simple and inefficient.Besides,because of the difference in method and principle,the fusion of submerged and non-submerged topographic data was difficult.But with the development of science and technology,advanced measuring instruments have been put into use on the data collection of channel slope.Using integrated measuring instrument to directly measure morphological,hydrodynamic and sedimentary characteristics of the bank slopes have a very large scientific value and practical significance.For this purpose we deployed integrated SeaBat-7125 multi-beam sonar,Riegl-VZ-4000 terrestrial laser scanner,Edgetech-3100 p sub-bottom profiler,double frequency ADCP,Trimble-DGPS and RTK to build a multimodal sensor system to achieve measurements of 12 typical channel slopes in the middle and lower reaches of the Yangtze River.Then we integrated the point cloud data of submerged portions of the slope with the non-submerged portions to achieve visualization of 3D morphology of channel slope.Furthermore,we calculate the stability and evaluate the development trend of the channel slope through dynamic,sedimentary and geomorphic features via BSTEM model.The main findings are as follows:(1)It is high efficiency and precision to obtain morphological,hydrodynamic and sedimentary characteristics data and establish integrated three dimensional landform models by using the multimodal sensor system.Besides,this non-contact measurement method is safer,more reliable and has wider applications than the traditional method.(2)Bank collapse in the middle and lower reaches of the Yangtze River mostly are arc collapsing and strip collapsing.Arc collapsing are mostly in pear-like shape,ear-like shape and crescent with scale ranging from tens of meters to hundreds of meters.The slope degrees are usually large and with near-shore recirculation.Strip collapsing usually extend in far distance and vertical flow is present along the near shore.(3)The vertical flow and circumfluence are important factors in bank collapse.The stronger hydrodynamic force can accelerate the destruction of river bank soil,scours the bank toe and makes bank slope steeper,which makes the bank instable.(4)The submerged slump block may also deflect flow onto the bank,thereby increasing the rates of erosion.The slump blocks may steer flow up,over,and around their topography and onto the adjacent bank.Therefore,the combined effects of large-scale recirculation flow and the submerged slump block reduce the stability of river bank.(5)In accordance with BSTEM model,if the safety factor is from 1.0 to 1.3,the slope is instable.If the safety factor is over 1.0,the slope is stable.According to the calculated results,the channel slope in Longtan site,Guniusha site,Guanyinzhou site and Jiujiang site are currently stable,which safety factors are 2.22~3.80,5.73~6.89,2.02~3.19 and 1.49~2.36.The channel slope in Taiyangzhou site,Luoshan site,Zhuanqiao site,Xihua site,Lujiahe site and Shishou site are currently local stability,which safety factors are 1.25~2.23,1.01~1.34,1.19~1.51,1.18~1.72,1.22~2.48 and 1.16~5.64.The channel slope in Meitanzhou site and Qichun site are currently instable,which safety factors are 1.01~1.21 and 1.21~1.29. |
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