Gravitational erosion in afflicted areas and its effects of sediment yield and transportation - A case study in Niujuangou gully

Niujuangou gully, the epicenter of Wenchuan Earthquake, was taken as the study area and the field observation stations and sections were established in the typical zones of gravitational Erosion such as rockfall, landslide and debris flow. Modern surveying and mapping technologies including GPS, total station and 3D laser scanning system were adopted and field surveying of slope, section, channel and surface deformation were conducted on different geo-hazard bodies. The development feature and the sediment yield and transportation were analyzed. The results showed tha debris flow is the typical of strong erosion and giant deposit with the maximum respective erosion and siltation depth of 6.84 m and 4.77 m only once. In the upper reaches of channel, debris flow shows erosion features with the maximum erosion depth of 6.84 m, and in the middle reaches of channel, the preceding debris flow takes on the super-elevation in curve ways with 2.2 m higher in concave bank than in convex bank and the later-period debris flow displays large-scale erosion with the maximum scour depth of 3.77 m. In the lower reaches of channel, debris flow shows accumulation features with the mean deposition thickness of 1.65m. Gravitational erosion has a violent effect of sediment yield and transportation with the mean sediment yield volume and accumulation thickness of 15.2×104 and 1.44 m as well as the maximum sediment transportation volume and scour depth of 16.2×104 m3 and 1.53 m. The results can be used as references for location line selection of key projects, river regulation and control engineering optimization design of mountain hazards.