Stability analysis on arc collapsing channel slope in the lower reaches of the Yangtze River based on multimodal sensor system

Measurements of arc collapsing channel slope in Tongling reach of the Yangtze River were made in September 2016. We deployed integrated SeaBat-7125 multi-beam sonar, Riegl-VZ-4000 terrestrial laser scanner, Edgetech-3100p sub-bottom profiler, ADCP, Trimble-DGPS and RTK to build a multimodal sensor system to directly measure morphological, hydrodynamic and sedimentary characteristics of the arc collapsing area. 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. Then we evaluate the stability and development trend of the arc collapsing with measurement results. The results show that the arc collapsing is concave with three ladder-like distribution in morphological characteristics, slopes of the non-submerged portions are between 0.09 ∼0.25, while the submerged slopes have reached 0. 33 ∼0.55. The collapsed bank material is 15 245.8 m³ and submerged blocks of failed bank materials which is 3 ∼ 5 meters thick were found at the bank toe. The riverbed is mainly formed with fine sand and medium sand, of which the medium particle size is 152.7 μm. ADCP data reveals that the recirculating flow with spead of 0. 14-0. 30 m/s is created within the arc collapsing and the combined effects of large-scale recirculation flow and the submerged slump block, therefore the location of erosion at the north-west embayment and the stability of the arc collapsing is poor.