Demarcation of High Hazard Areas Based on Human Stability Considerations in Tsunami Overland Flow

On December 26, 2004, the coastal belts of Sri Lanka and several other countries bordering the Indian Ocean suffered massive loss of life and damage to property due to the tsunami unleashed by the third largest earthquake ever recorded. One way of mitigating potential loss of lives from a similar event in the future is through advance warning of an approaching tsunami and quick evacuation of vulnerable coastal communities to safer areas. The detailed planning necessary for such evacuation exercises requires information about the level of hazard in each locality, which is usually based on inundation maps showing the depth flooding. However, the ability of a person to survive a flood flow depends not only on the depth of inundation but also on the flow velocity. Accordingly, the present paper employs a numerical model to compute the temporal variation of both the flow depth and the flow velocity across the entire computational domain in three cities on the south coast of Sri Lanka as well as the results from an experimental study on the human stability in tsunami overland flow to develop a procedure to demarcate the areas that should be evacuated in case of a tsunami warning.