DRAINAGE OF WATER INTO SMALL CHANNELS

In the survey area, a topographically interesting phenomenon was observed at places where the tsunami was higher than 5 m. In some small channels that flow into the sea and had a channel width of about 1 m prior to the tsunami, the width at a few locations increased to over 30 m after the tsunami. This widening was observed for several hundreds meters upstream from the river mouth. Photo-3 shows one example.

According to local residents, the channel width did not increase at the time of tsunami runup; instead, it occurred when the flood retreated and water was trapped in small channels at relatively low elevations. Currently, authors do not have enough information to explain this phenomenon. We would like to elucidate this drainage mechanism of water flowing into small-scale topographical undulations.

Photo-3 Channel widened at the time of water retreat (The location is on the shore nearly 15 km north of Trincomalee City. The photo was taken looking upstream from the river mouth.)

• SURVEY ON TSUNAMI RUNUP IN THE RIVER
  1) Yan Oya
  2) Mahaweli Ganga
  3) Comparison with the tsunami runup in the river in Japan
• DRAINAGE OF WATER INTO SMALL CHANNELS
• DAMAGE TO BRIDGES, AND NEARBY TSUNAMI TRACES