Report on Asian tsunami ascending the river, and its associated bank erosion and bridge failure in Sri Lanka

摘要

Field survey was conducted on tsunami intrusion and runup in the Yan Oya River, whose estuary is about 500 m wide, and the Mahaweli Ganga River, whose estuary is about 200 m wide, both of which disgorges into the Indian Ocean from Sri Lanka's east coast. That coastline was directly hit by a tsunami generated by an undersea earthquake off the island of Sumatra in Indonesia. In order to understand the mechanism of tsunami intrusion in a river channel, it is extremely important that the estuary topography, coastal tsunami behavior and riparian vegetation cover must be understood, as they influence the movement of a tsunami. It was confirmed that riverbed fluctuation and sediment transport occurred with the tsunami intrusion, and that this inflow brought several dozen centimeters of sediment, most of which washed out by backflow.