Abstract:

The middle and lower portions of Vu Gia - Thu Bon catchment are underlain by complex structure and morphology. The area comprises many sedimentary and magmatic rocks of Precambrian to Cenozoic in which Quaternary sediments cover most of the lower river basin. These rocks are cut by many fault and fracture systems of different sizes, which dominantly trend northeast-southwest, northwest - southeast, longitudinally and latitudinally. Some fault systems were active during Neotectonics, evident by the deformation of young geological assemblages, uplift and subsidence, and modification of drainage systems. Within the study area, many types of geological hazards such as landslides, river bank erosion and coastal erosion are occurred. They are commonly controlled by endogenic movements in combination with other exogenic processes. Landslides commonly occur within the zones of strong faulting or fracturing of the rocks. River bank erosion commonly takes place at the intersection of river with active faults or the change of flow direction due to uplift or subsidence. Coastal erosion takes place in the areas of subsidence that leads to relative sea level rise. For mitigation of landslide risks, a workable solution is to unload the slope block and reduce the slope angle, draining of water together with enforcement of the slope with suitable dams. For the river bank erosion mitigation, a combination Iowa vanes construction and reinforcement of the river bank by geogrids and grass growing is a suitable solution for unstable banks. For the mitigation of coastal erosion, constructing near-shore headland breakwaters and reinforcement of the shore by geogrids, together with a sustainable coastal management planning is one of the effective way to reduce the ricks of coastal erosion in the context of coastal zone subsidence coupled with long-term sea level rise caused by global climate change.