High-resolution inundation modelling with explicit buildings : a case study of Wellington CBD

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Wang, X.; Lukovic, B.; Power, W.L.; Mueller, C. 2017 High-resolution inundation modelling with explicit buildings : a case study of Wellington CBD. Lower Hutt, N.Z.: GNS Science. GNS Science report 2017/13. 27 p.; doi: 10.21420/G2RW2N

Abstract: The effects of Explicitly Representing Buildings (ERB) on the estimate of tsunami flow depth and flow speed were investigated at Wellington Central Business District (CBD) in New Zealand, using an Mw 9.0 Hikurangi subduction zone earthquake scenario. With modelling grids at 1.5 metre horizontal resolution, individual buildings were treated as solid-filled blocks and assumed to remain standing during tsunami impact. The latter is likely to happen in well-built urban areas such as Wellington CBD. The modelling results reveal that in most of the CBD areas maximum tsunami flow depths using the ERB approach are about 0.5 to 1.0 m higher (i.e. typically > 40%) than those modelled using the widely-adopted roughness approach, in which buildings are removed and replaced with Equivalent Surface Roughness (ESR) values. In most on land waterfront areas and in the harbour water, the ERB approach gives an estimate of maximum flow speeds typically 1.0 to 3.0 m/s higher (i.e. typically > 80%) than the ESR approach. The large differences between the resulting values of each modelling method imply that there are potentially large (and previously unrecognised) underestimations in tsunami loss and risk assessments that use the maximum flow depth (and flow speed in some models), commonly obtained with ESR approaches, as key parameters in evaluation functions, especially in urban areas. The flow depth increase will also reduce the margin of safety for safe height for vertical evacuation determined by the FEMA guideline which uses flow depth as the sole parameter. (auth)