Remarkable bathymetric change in the nearshore zone by the 2004 Indian Ocean tsunami: Kirinda Harbor, Sri Lanka

We investigated bathymetric data obtained at Kirinda Harbor, Sri Lanka one month before and 2 and 11. months after the 2004 Indian Ocean tsunami. Our bathymetric surveyed data and numerical modeling results suggest that the first run-up tsunami wave transported huge amounts of offshore sea bottom sediment and deposited it in a layer up to 4. m thick along the shoreface slope. In some places, this accreted sediment was not eroded by the backwash because of the particular arrangement of artificial structures and sand dunes. Especially, the sedimentation process and the volume of the sediment transported by the run-up waves can be examined where the influence of the backwash flow was very minor. Remarkable sedimentation attributable to the run-up wave would have occurred mainly by the deposition of the sediment particles along the slope by the run-up waves; the slope was developed toward the stoss side rather than by the settlement of the sediment from the suspension load. We estimated that considerable amounts of sediment were transported by the tsunami from the offshore sea bottom, but most were deposited not on land but in the sea. Eleven months after the tsunami, the harbor bathymetry had almost undergone complete reversion to its pre-tsunami condition, implying that the tsunami impact on permanent geomorphological landforms was limited at this harbor.