Everything shaded on the map is council or GNS Science data, unchanged. The walking routes, the aiming points and the barriers are mine, and they are the parts most likely to be wrong.
Kāpiti's three tsunami evacuation zones were defined by GNS Science using COMCOT, a hydrodynamic model that simulates a wave from its source across the ocean and onto the land. The council publishes them as spatial data, and this page draws that data directly rather than tracing it.
One thing worth knowing, because it is not obvious from the map: the three zones are adjacent bands, not nested rings. Red sits against the shore, orange behind it, yellow furthest inland, and they abut rather than containing one another. Being outside the yellow polygon is not the same as being out of danger unless you have also cleared the other two — which is why this tool routes to the far edge of all three.
| Zone | Modelled from | Recorded height |
|---|---|---|
| Red — Shore Exclusion | 22 distant-source scenarios at the 1 m threat level, checked against the national rule of land under 2 m above high tide | up to 1.2 m wave; runup ≈ 2.5 m above MHWS |
| Orange — CDEM Evacuation | 29 scenarios at the 3 m threat level and 20 at 5 m, all distant sources | up to 5.0 m wave height |
| Yellow — Self Evacuation | 50 non-uniform slip scenarios on the Hikurangi subduction interface, 8 on the Fisherman Fault, 1 on the Manaota Fault | up to 10.0 m wave height |
National guidance asks the yellow zone to cover at least the inundation expected once in 2,500 years, at 84% confidence. GNS reported that where the modelled scenarios overlap, the return period could be well beyond 7,300 years. For comparison they estimated the Wellington Harbour yellow zone at around 6,000 years.
So it is a rare event. It is also the one with no warning: the shaking is the warning, and the council puts a local-source arrival at as little as three minutes.
GNS computed maximum flow depths for every modelled cell. Only the inundation extents were released. That means neither residents nor the council can tell from the published data how deep the water would be at any particular place inside a zone — which is why this tool routes to the edge of the zone rather than to a chosen elevation, and why no height on this site is presented as a safe height.
The council's own data records the method behind each zone. Kāpiti Coast District Council has one entry: COMCOT hydrodynamic modelling, 2017. Every other territorial authority in the Wellington region has a mixture, and most still include zones drawn with the 2008 attenuation rule — a geometric rule of thumb rather than a simulation. On this measure Kāpiti has the best-modelled evacuation zones in the region.
That provenance is only discoverable by querying the map service directly. It is not shown on the council's public map.
Zone boundaries: Mueller, C.; Power, W.L.; Wang, X. (2017).
Tsunami modelling and evacuation zones for Porirua and Kāpiti Coast. Lower Hutt
(NZ): GNS Science. GNS Science Consultancy Report 2017/200.
Elevation: LINZ Wellington–Kāpiti Coast 1 m LiDAR DEM (2024), CC BY 4.0. Addresses: LINZ
NZ Addresses. Walking routes: OpenStreetMap via the Valhalla routing engine. Basemap:
© OpenStreetMap contributors.
It works out a walking route from an address to the far edge of the zone, and then on to the nearest assembly area. It prefers hand-chosen aiming points where local knowledge beats geometry, and it refuses routes that head towards the water or cross a barrier.
It knows nothing about locked gates, private land, fences that went up last year, paths that exist on a map but not on the ground, watercourses in flood, or damage after an earthquake. Only someone who has walked it can tell the difference — which is the whole reason for the feedback form, and for walking your route before you need it.