Will a Storm Surge be Predicted for Whangateau Harbour?

A king tide on the 22nd February, 2015 reaching a level of 200mm from the surface of the road at a new sub-division at Point Wells. The tide covered the footpath leading to the shore  and small fish were swimming up the drains into the low lying sections near the waterfront. Survey pegs of some sections were under water. A storm surge could increase this incursion dramatically.

A king tide on the 22nd February, 2015 reaching a level of 200mm from the surface of the road at a new sub-division at Point Wells. The tide covered the footpath leading to the shore and small fish were swimming up the drains into the low lying sections near the waterfront. Survey pegs of some sections were under water. A storm surge could increase this incursion dramatically.

As cyclone Pam bears down on New Zealand after wrecking havoc in Vanuatu it would be useful to know how a tidal surge from the storm would affect the low lying land around the harbour. Is any such information available?

A storm surge happens when a large storm approaches and passes over a coastal region. This surge happens when the sea level rises from a number of factors. The two main meteorological factors contributing to a storm surge are a long fetch of winds spiraling inward toward the storm, and a low-pressure-induced dome of water drawn up under and trailing the storm’s center. The second effect is responsible for destructive meteotsunamis associated with the most intense tropical systems. These surges can be as high as 13 metres and are commonly 8 to 10 metres. These tidal surges combine with the normal tides in a region and together with the additional wave action can overwhelm low lying areas in a severe storm.

There are models to predict the incursion of storm surges developed for the coastline of the United States for their tropical cyclones (SLOSH) and their extratropical systems (ESTOFS). By the time cyclone Pam reaches us it will be classified as a post cyclonic and extratropical storm. Have these prediction models been developed for New Zealand and are they being used by the local civil defense to warn the residents of Omaha and Point Wells of any potential danger from the storm?

The models that NOAA (National Oceanic and Atmospheric Administration) use are described here.

Comments

  1. Vernon Pryde says:

    You do your self no favours, presumably your artic le is to raise public awareness of issues effecting Whangatau harbour yet reference ” storm surges commonly reaching 8-10 metres”. Wake me up when the next 8 metre surge enters our harbour!

  2. If there is an 8 meter surge Vernon could be hard to wake up.

  3. Ian Macdonald says:

    I don’t think anyone knows whether an 8m tidal surge could happen in Whangateau Harbour. This is the question I ask? There certainly is historical evidence of a tidal surge or a tsunami of that size from the direction of logs in the peat on the Omaha Flat and the lie of submerged large trees in the kahikatea on the Mangatawhiri Spit. I would have thought if there was proper dynamic modelling available as there is for the United States coast when a cyclone is approaching then it would enhance the safety of residents who choose to build and live at the water’s edge. The point I make about the subdivision in the photograph (and referred to in other posts on this site) is that it would need a storm surge of only 200mm or greater to produce a tidal surge that would flood the subdivision at a king tide of 3.7m.

  4. Marie Ashton-Jones says:

    As a local growing up here in Whangateau i have witnessed a storm that went over the walls and inside of my grandparents and family batches, hill erosion where it came down and destroyed half the building of my uncles batch in Lews Bay and rebuilding the wall 3 times allowing for sea levels increasing. My grandparent view on this was because of the sand being removed at the tip of Omaha beach. This stopped and the result of this was whenua loss. Boulders were placed to support the rebuild of the sand dunes and are still there to this day. Recently we have all undergone flooding to an ultimate extreme never seen in my aunties life time, who is 92 due the extreme rain conditions, no correct council drainage, blocked estuary of land slips, trees. For the water to go over the one lane bridge at whangateau, is massive. The surge of water coming from the road had no where to go but into the estuary. This roll on effect caused it to surge back up into our properties into sheds, houses etc. The tusunami alarm in our area has certainly been a proactive move on behalf of the civil defence for enhancing safety of residents. The large storm several years ago with the king tide did effect this area where people could be seen kayaking in our whangateau domain. Residents over the road near the water edge were effected but our house not. Recently our members of my family walked out to the water edge. There they found 40ml of dirt covering alot of sand areas from land though to water edge mark and the smell was terrible. Oh no our poor pipi and cockle beds are suffering once again. Yes we do chose to live here, for some of us it has been our family whenua from early setters years and Maori more so. The unmistakable question is; Is our sea level rising? my opinion yes it is. Yes we are vulnerable. Nature has a kaupapa of its own. Its what we can do now in educating the next generation to be proactive of carers of our earth.

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