- - - - - - - - - - - - -

Tuesday, December 16, 2008

Auckland motorways barely survive King tide

It's the afternoon rush now as you can see by the traffic going West. The image from Transit looks across the NW motorway causeway crossing one of the estuaries of the inner Waitemata - you can see the tide is going out. At 11am today was high tide - a King tide I've been told given the Moon's influence at the moment - and it submerged the cycle lane (on the extreme left of the image) for several hundred metres reaching about a foot deep over many parts. I took the time to walk along it earlier today and witness nature's extremes. Well, sort of - a 3.5m tide isn't that extreme, I've seen higher, but this was more impressive than I expected when I set out.

Small crabs - some aggressive - were crawling in the sea, over the asphalt pathway. Cyclists and moped riders had to turn around and go back. At one place the sea was actually at the white line of the run-off/bus lane and it was not rough weather either it was flat. On the Northern approach to the harbour bridge the causeway is similarly low-lying and I would expect the same perilous proximity occurs in stretches of the southern motorway too.

If rising sea levels are occuring then I would expect to see the tide cross some of these parts of the motorway in King tide events in the next few years. If. Especially if it coincides with heavy rainfall and/or a storm.

[UPDATE:
Perigean-spring tides. - NIWA The table suggests this morning's tide was just under the peak of yesterday and will be the highest for some time.]

3 Comments:

At 16/12/08 5:31 pm, Blogger Steve Withers said...

Worth noting for future reference. Ta.

 
At 16/12/08 5:38 pm, Blogger Tim Selwyn said...

Sorry - no pictures. But thousands of people in the traffic would have seen the full extent of it.

 
At 17/12/08 2:08 am, Anonymous Anonymous said...

3 low points on SH1 - southern motorway - in Auckland (CBD to Bombay hills).

* Small SH1 bridge over Tamaki estuary inlet just north of Otahuhu (c. 2m high tide clearance)
* Tamaki estuary SH1 bridge between Highbrook Dr and Otahuhu (c. 2m high tide clearance)
* Slippery Creek SH1 overbridge just north of Drury interchange - limit of tidal inflow from Manukau harbour (c. 3m high tide clearance).

The NW and Northern motorway sections Tim mentioned are the lowest, barely 1.5m above high tide. But both can readily be raised in height, though this will cost tens of millions. Cheaper to build dykes alongside motorway to keep high tides out.

 

Post a Comment

<< Home