MethodologyIn 2012, Hawke's Bay Regional Council conducted a tsunami computer modelling exercise for the Taranaki coast using 2 m and 4 m waves. This 2017 updated report provides the results from additional model runs using a wave height of 10 m. The 10 m wave height is considered to have a return period of well beyond 2500 years, as the height is not reached in any of the tsunami hazard plots from the 2013 National Tsunami Hazard Model (Power, 2014). The decision to include such a wave height was in order toshow inundation extents that covered any conceivable wave height, up to and including a value (10 m) that is easily visualised by the general public.The highest wave amplitudes were applied at mid-tide levels. The wave heights are applied such that the 2 m wave rises 1 m above and falls 1 m below the normal tide, the 4 m wave rises 2 m above and falls 2 m below the normal tide, and the 10 m wave rises 5 m above and falls 5 m below the normal tide. The timing between the peak and the trough was set to 20 minutes. This was based on anecdotal evidence from recently occurring tsunami from Indonesia, Chile, Samoa and Japan. These waves were applied to the offshore boundary. 2D models were used in the main locations of New Plymouth, Opunake, Patea, and Tongaporutu and Waitara which meets the defintion of Level 3 developmental levels for modelling according to DGL 08/16.For all other areas the attenuation rule developed by GNS (2009, Leonard et. al, and 2013, Fraser S., Power W.) was employed which meets Level 2 developmental levels for modelling according to DGL 08/16. The rule has been shown to provide reasonably accurate representation of inland inundation from tsunami based waves. The application is as follows: For a given shoreline wave height, the wave height was added to a mid tide value (in this case 2 m), then the following attenuation rules were applied: - The potential runup height attenuates at a rate of 1 m for every 200 m horizontal inland for flow direct from the coast. - The potential runup height attenuates at a rate of 1 m for every 400 m horizontal inland for flow up a significant river-- The potential runup height attenuates at a rate of 1 m for every 50 m horizontal inland for flow over land away from a significant river. The application of these rules was by a manual method using contours (where available) while estimating where the attenuation line would intersect the appropriate ground contour.It should be stressed that the informaiton presented relatig to the 10m wave is very extreme in nature abd should not be used by local authorities to delineate specific properties as bein gwithin the inundation area, and therefore subject the proeprty to a notice on a Land Information Memorandum.Report name: Taranaki Tsunami Inundation Analysis, prepared by Craig Goodier Principal Engineer (Modelling), Hawke's Bay Regional Council Asset Managment Group, June 2017, HBRC Plan Number 4396Source: Taranaki Regional Council (TRC)Contact: Chris Lambert
