“Standing on shaky ground, ever since you put me down…” sang the Temptations and it resonates deeply with people of Wellington. We all know that our isles are shaky, and our city has the potential to be shaky in the extreme, but what we perhaps don’t know is just how shaky our particular patch of dirt is beneath our own two feet. I’ve been doing a bit more looking into this – starting with this post we blogged on Tsunami and then I found this other study, on Wellington’s rocky substrate. It’s quite an eye-opener.
Obviously the WCC District Plan maps “seismic shaking zones” are based on these ground maps, and the maps are based on thousands of underground bores that have been drilled over the city. I can’t find the source document any more – if anyone knows what it is, please let me know so I can rightfully credit it. (Post-script: thanks to GK, the source document is noted as Semmens, S.; Perrin, N.D.; Dellow, G.D. 2010. It’s Our Fault – Geological and Geotechnical Characterisation of the Wellington Central Business District, GNS Science Consultancy Report 2010/176.)
Anyway, based on this info, the report’s authors have managed to make up a fairly good illustration of what is happening beneath the streets. And this has profound effects on where and how we might want to build in the city. For instance, I’ve long been under the impression that the growth areas were likely to be Te Aro, Newtown, and the part of Adelaide Road in between. I suspect the City Council have been feeling that way too, because they called that part of the Growth Spine.
But is this all going to come unstuck? The thing that stands out to me is just how poor the ground quality is along certain routes in the city, and logically the ground is poorer where there used to be a waterway. And waterways tend to run down the lowest points of the valley. And the biggest valley we have in Wellington extends all the way from what must have once been the boggy marshes of Newtown, down Adelaide Road, into and through the Basin (which was seriously proposed as the site for Wellington’s harbour in the very early maps), down Kent/Cambridge Terrace, and merrily splashing into the sea at what is now the Port Nicolson Yacht Club. Basically, there is still a watercourse there – there are brick culverts under the Basin with several species of fish living in them – and while its not quite the case of “a river runs through it”, there’s none-the-less a lot of water running under our streets. Especially down Adelaide Road and Kent Tce, but also: everywhere.
I thought it may be interesting to see how well the two maps coincide – the WCC ground shaking zones, and the GNS “It’s Our Fault” report on Wellington subsoil conditions – so we’ve made a Gif that morphs between one report to the other. What is interesting to me is that while there is close correlation between the two, they are definitely not the same. Close but no banana.
Actually, most of it has some close correlation – but in the region around Kent/Cambridge, the effects are far more widely spread. The WCC map (which I coloured in bright turquoise blue) is much narrower, while the GNS report is much wider. Both maps rightfully regard Courtenay Place as a right-off. That itself is something that Maximus wrote about way back in 2014 where Max noted the words of an early pakeha settler, who said in 1859: “Mr Plimmer also mentions that Te Aro flat was covered with fern and flax, except that portion of it extending from Courtenay Place to the Basin Reserve, which was one impassable bog. A friend told the writer that in 1859 he would walk out of the back door of the house in Courtenay Place – walk a few paces, then jump up and down and watch the jelly like movement of the ground for a considerable distance around.”
From the Cyclopedia NZ vol 1, p245
Don’t know about you, but that send a few shivers up and down my growth spine – Max went on to write, in his own descriptive manner:
“Just imagine – the very site that the writer was describing back then, could be the very site of Boogie Wonderland today. Those same tendencies still exist in Courtenay Place today – walk a few paces, jump up and down, and watch the jelly ripple… But we’re talking about a different seismic event. Nowadays, it’s dance party central, and the ripples are the waves of muscle, flesh, and sub-visceral fat that permeate the bodies of the young groovers who shake their booty on the dance floor. So, there may well be historic reasons why high-rise building has not taken place much on the Te Aro foreshore until today…”
“In 1853 Te Aro swamp burst through the narrow bank which separated it from the sea. The bursting caused a loud noise, which was heard from a considerable distance, and covered the town acres in the waterfront.
Te Aro flat was merely flax bushes, fern and streams, where inungas and eels could with very little skill be easily captured, and where cattle that had been pushed overboard in batches from the ships near the waterfront of Bethune and Hunter’s and other places on the beach, sometimes took charge of the town and defied the efforts of the bullock punchers in charge to pen them in the yards provided for them in the vicinity of Manners Street. Numbers got bogged in the swamp, where those that could not be rescued by horsepower were left to perish. In 1855 the earthquake disintegrated the swamp, and small islands of flax and toi-toi were floating about the harbour and interfering with the passage of small coasters in the area. At the same time the whole area was raised.”P304.
From Early Wellington – By Louis E Ward.
“Strange to think of Courtenay Place as a swamp full of eels and toi-toi only 150 years ago. We have all heard that Cambridge / Kent Tce was the route of the Waitangi Stream, but it is a bit disconcerting to read that the whole of downtown Te Aro was built on a 150 year old jelly / eel pie. Hmmmmm. Not so tasty after all. Looking at the new Elevate Tower Apartments that have just gone up 17 storeys high on the site of, what was, until recently, a sandy beach near Te Aro Pa, makes me nervous. Have the geo-tech engineers got it right? Have the pilers reached rock-bottom, in a very literal sense of the word? Fingers crossed.”