Validation of GIS-based attenuation rule for indicative tsunami evacuation zone mapping

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Fraser, S.A.; Power, W.L. 2013 Validation of GIS-based attenuation rule for indicative tsunami evacuation zone mapping. Lower Hutt, N.Z.: GNS Science. GNS Science report 2013/02 18 p.

Abstract: A GIS-calculated attenuation rule for development of indicative tsunami evacuation zone has been previously developed and presented by Leonard et al. (2008). This provides a solution for tsunami evacuation zone planning where a lack of resources or detailed topographic and bathymetric data precludes full hydrodynamic simulation of tsunami to develop evacuation zones. Attenuation of tsunami flow over land is considered to occur at different rates, dependent on the flow path – i.e. over land from the coast, along a river channel and laterally from the river, or into a harbour then over land. The attenuation relationships applied in the method were calibrated using inundation data collected during several post-tsunami field surveys. The method has been applied in several cases of evacuation zone mapping in New Zealand and the Pacific. However, since its development and application there has been no validation of the method with recorded inundation data. The present study succeeds in validating the approach by comparing outputs of the attenuation-rule based method against inundation and run-up data points surveyed following the Great East Japan Tsunami (11th March 2011). To validate the method, firstly the inundation height versus distance inland (according to the attenuation rules for overland flow from the coast and via rivers) is directly compared against the survey data points of inundation and run-up height. Secondly, GIS-calculated evacuation zones are developed for two contrasting study areas in Miyagi Prefecture, Tôhoku, Japan, representing coastal plain topography and a rias (drowned river valley) with harbour topography. These are then compared to the recorded survey data and satellite imagery indicating tsunami inundation extent at the same locations. The evacuation zones generated using the GIS-calculated attenuation rule successfully incorporate the zone of inundation due to the Great East Japan tsunami at both study areas, giving confidence that the method is suitable for derivation of indicative evacuation zones elsewhere. (auth)