Search This Blog

Friday, 16 September 2011

Why an Avonside Orange Zone?

It looks like it will be some time before we find out how the Avonside Orange Zone will be redesignated. It might be possible for some to hazard an educated guess which way things will go, but it isn't worth the grief it would cause. What is worth looking at is why we have an Orange Zone here, and why everything is taking so long.

When Gerry was talking earlier about zones being blindingly obvious he was correct, in an obscure way (a touch of the Winston Peters malaise perhaps?). The bulk of the information was contained in the Tonkin & Taylor factual reports, and reasonably accurate conclusions could have been drawn from them by anyone with a bit of expertise.

Sadly, or maybe wisely, no one with the expertise to draw valid conclusions attempted to do so, and the media were not able to work it out for themselves. Those same reports will possibly explain, albeit indirectly, why some Orange Zones exist.

What follows is my very inexpert assessment of why our Orange zone was created - provided in the absence of anything from anyone else. Read at your own peril (NOTE: conspiracy theorists need not proceed further - there isn't one).

Why is there an Orange Zone here?

If we look at the the Tonkin & Taylor definition of Avonside from their February 2011 Factual Report (p 16), which was based solely on the land issues arising from the September 4 earthquake, we get the following:

Not quite Avonside the suburb as it has been used by real estate agents and residents, but a clearly specified area.

The June Zone map has the bulk of Avonside, as defined in the T&T map above, in the Red Zone.

Much of the map is obvious, except that land between Highbury Place and the top of Patten Street has been made Orange. Everything else to the south of Avonside has gone Green (to Woodham Road).

Okay - so how is it that there is uncertainty for land immediately south of Retreat Road and the bottom end of Silverdale Place?

The official line is that the earthquakes of June 13 further changed the nature of the land in some parts, and created more uncertainty. As there are no geotech maps available no one knows what the changes were, however I would speculate that prior to the 22nd of February only land north of Retreat Road was under suspicion.

The photograph below is from P17 of the T&T Factual Report. At the bottom left is AGHS and Retreat Road runs across the upper half of the photograph. The numbers and symbols relate to boreholes and other geotech analysis sites. It is hard to tell from the photograph but all except two sites are on the north side of Retreat Road (but nothing in Silverdale Place). The exceptions are both in Retreat Park.

The significance of this? My speculation is that only the land north of Retreat Road was under suspicion. The geotechnical assumption was that land south of the road was okay, and so no investigations would be needed in Patten and Cowlishaw streets, or points further south. Under normal scientific conditions random sampling would have taken place to test the assumption. The enormity and urgency of the situation probably pushed everyone in the direction of intuitive sampling.

Obviously February 22nd changed perceptions about the land, however in the absence of data for land south of Retreat Road, it was a matter of starting from a zero base. June 13 pushed things further out.

That, in my view, is why we have an Orange Zone. The concept of "blindingly obvious" is suitable for political and media discussion, however anything requiring scientific support, especially where money and litigation will be involved, requires evidence more substantial than what the eye can see. Until that is available and assessed, we are in something of a purgatorial middle place**.


The first earthquake occurred on September 4 and the Avonside Factual Report was not released until approximately 6 months later (the Report is dated February however it wasn't released until March).

Assuming assessment of the impact of the February 22nd earthquake was a least as intensive as the first round, and this time complicated by insurance considerations, a similar 6 month period would be quite tight and take up to the end of August. The June 13 earthquake would have come approximately 4 months into these investigations and rendered some of that work irrelevant.

A consequence of these things is that the current timelines are reasonable, based on the effort required in the past. When you also factor in that the interpretative report on Kairaki Beach got it very wrong (the considered opinion was that the land was good and would survive another earthquake; which it didn't) getting things right is going to be very very important, and far more important than doing it quickly. How you factor in the human carnage arising from each extra day I don't know.


There is an Avonside Orange Zone because that area was presumed sound prior to the 22nd of February. After the 22nd no one was sure where the boundary lay between sound and unsound land. As the consequences of getting it wrong will be both tragic and expensive, getting it sorted will take as long as it takes.

** Not quite as Dante would have it, but near enough.

No comments:

Post a Comment

Note: only a member of this blog may post a comment.