Earth to Kirk: Junk Science makes Bad Policy

There is an article headed "Dunes Crucial Defence" in Wednesday's (Jan 19, 2004) Christchurch Press 'Perspective', by Professor Bob Kirk. It's notable in several aspects. It defends and summarizes the current position of Environment Canterbury - a not surprising advocacy. It borders on the mischievious in conflating a Charteris bay tsunami damage photograph with discussion of Pegasus Bay foredunes. It neglects to differentiate tsunami effects based in the elementary classifications of source and destination. It glosses over the inconsistencies in both the extent and likely effectiveness of the dunes as a primary defence. And it omits entirely any reference to the practical effects of all this, as it relates to the current Catch-22 policy situation applying to Central Brighton development.

It is no new story, that New Brighton has seen better days. St Kilda, Melbourne had the same sort of reputation as does Central Brighton - seedy, run-down, and generally unattractive. A Brighton revitalisation project is, in broad terms, underway. But real revitalisation takes private capital, higher population density, the attraction and retention of higher-discretionary-income residents, and the emergence of services, facilities, retail, restaurants and other niches, to serve this population. This can be seen now at St Kilda, where the quirky retail strip has become a fashionable destination.

But back in struggling Brighton, apart from the Pier and the Library, little in the way of actual, on the ground revitalisation is apparent. The current event-based effort does attract day trippers with some spin-offs for the local retail scene. But, honestly, an essentially transient audience attracted by jugglers, clowns and buskers is no substitute for a more discriminating population of permanent residents who (together with the day visitors and a wider selection of events) can more readily support the sort of niche shops one finds in St Kilda - excellent art bookstores, the best gelato stand in Melbourne, European cakes and confectionery, a thriving range of slightly alternative retail, and all this interpersed with banks, insurance, property agents, telcos and restaurants. That is, of course, just an old seagull's vision. Jugglers and clowns are necessary for the contentedness of the wider population - ask any Age of Empires gamer. But, and this is the essential point, this revitalisation stuff cannot be done other than by the private sector. It is emergent rather than planned, and what emerges is more akin to a biological process than to bullet points on a Revitalisation Policy document.

So what's stopping a private-capital-funded Brighton renaissance? An unholy if perhaps unintentional combination of Council land-use policy and the continuing wrangle over the dunes and sea views. It can be seen as a classic Catch-22 - the present L3 zoning allows 10 metres high/three storeys. But the dunes (where they exist, of which more later) average 8 metres high, effectively cutting out sea views. Hence, there's no incentive for developers to build as things stand, and a glance along the narrow-dunes strip from Rawhiti Park south to Rodney Street will confirm that that's exactly what's happening. Nothing. It's hard to sell apartments with the pitch "You've just paid $650,000 for your unit. Here's your view - of glorious marram grass, sand and ice-plant".

The natural reaction of developers is being followed: applications for consents to move above the 10 metre mark, and a concomitant desire to lower the dunes. But the Council has decided, on the basis of staff advice, to think everything through slowly as a formal District Scheme change, rather than to decide cases quickly on their individual merits. This may have superficial appeal. But it is having an absolutely chillng effect on development - already financial difficulties are apparent amongst the backers of at least one project, and this can be explained by the sudden increase in the holding time needed between section purchase and start of building. In effect, by opting for a Scheme change and throwing the door open to a raft of Christchurch-wide objections, comments and discussion, the Council has imposed opportunity costs upon developers, which conceivably run to millions of dollars over the rather leisurely Scheme Change timeline. Hence the chill.

And what of those dunes, and their 'crucial defence' element? The City Council depends on Enviroment Canterbury for advice on this, and any changes of dune height need a consent from EC. The problem with the EC position of dune height is simple: if the dunes are 'crucial' as alleged, then what about the stretches where there aren't any (Central New Brighton, the Avon-Heathcote Estuary mouth) or where the height is substantially less than the fabled 8 metres? Surely, in those areas, there is no 'front line' of tsunami defence.

A tsunami, for the record (US Geological Survey definition) is "A sea wave of local or distant origin that results from large-scale seafloor displacements associated with large earthquakes, major submarine slides, or exploding volcanic islands." The two defining characteristics of tsunami are a long period (15 to 60 minutes) and very high energy.

So it is necessary to differentiate our tsunami. For, as history shows, the same tsunami can have a markedly different effect on different destination shores. And the source of a given tsunami is also critical in those effects. Let's characterise source as Near tsunami and Distant tsunami; and destination as Pegasus Bay, Estuary and Avon/Heathcote rivers or the Peninsula Harbours and Bays.

The effect of a tsunami, and hence the mitigation efforts which can reasonably be put in place, varies. If we place these in a matrix of Source and Destination, we can from historical tsunami run-up records see something of this variation.

Far Tsumani - Pegasus Bay
Run-ups (the recorded maximum height reached) have not exceeded 2 metres over 150 years. In Central Brighton (where no dunes have ever existed) there has been no significant damage caused by tsunami run-up.

Far Tsunami - Estuary and Avon/Heathcote rivers
Waves over the Moncks Bay road at mid-tide (May 1960, referred to by Brown and Weeber, in their 1992 publication "Geology of the Christchurch Urban Area") and many instances of the Avon holding up and back-flooding parts of the Spit and South Brighton, particularly at lunar high tides, and not only from tsunami.

Far Tsunami - Peninsula Harbours and Bays
Significant run-ups - 5-6 metre high waves in Lyttelton (August 1868, May 1960), Henry and Ann Bailey's Le Bons Bay house swept away (August 1868, Ogilvie, 'Picturing the Peninsula", 1992). Generally, large, destructive waves.

Notice that the effect on the Peninsular Bays is quite different? In general, according to Brown and Weeber, tsunami have "particularly strong effects in the harbours of Banks Peninsula" because of the seabed configuration. There are two reasons for this.

The first is that there is a substantial seabed gradient just outside the mouth of most of the eastern bays (such as Hickory, Le Bons and Little Akaloa). The regular NZ632 chart (Maritime map) shows this quite clearly. The rapid decrease in depth causes a tsunami to 'rear up' and break onshore. However, Pegasus Bay (especially the southern end) has a substantial bank of post-glacial sand (the Banner Bank) in the northward lee of the Peninsula, for some kilometres out to sea. The seabed depths decrease gradually toward land, and wave energy is partially dissipated by friction over this extended distance. Waves which do reach the beach tend not to break as much as slop.

Secondly, bays and harbours tend to focus and can amplify incoming waves - this is the 'embayment effect', where energetic waves act unpredictably in a confined space. Owners of Tory Channel (Marlborough Sounds) baches will have experienced akin to this effect when the fast ferries were introduced and before speed (and hence energy) restrictions were imposed. The ferrys' propulsion is from water jets, four in all, with 9000 Kw to power each one, moving tens of cubic metres per second of water. The energy from those jets manifested itself as waves which travelled along the channel bottom, then literally reared up onto the beach frontages, carrying with them rocks as big as 30cm across, and all manner of channel-bottom scourings. Multiply the energy by several thousand times, and place it in a tsunami situation: the embayment effect is a real killer. It is this effect which the 'Perspective' photograph depicted - in Charteris Bay. And hence the mischief: this is emphatically not the effect which occurs on the Brighton beach shore.

So much for Distant Tsunami. Spot the omission? No Near Tsunami has ever occurred. There is a substantial fault in Pegasus Bay, which could generate the vertical movement necessary for a tsunami. We simply don't know what might happen. But if the experience of New Guinea in July 1998 is anything to go by, there is little warning time available. A 7.1 magnitude quake in the fault system nearby, offshore, generated a series of 10 metre plus waves which had sufficient energy to overtop an entire 100 metre wide spit, wash several hundred houses into a lagoon, and which waves were still sufficiently energetic even after that to penetrate another 1.3 km inland. (source: NOAA photographs and text captions, accessed from the Tsunami Runup database)

It's a fair bet that a similar event in Pegasus Bay would cause waves that were energetic enough to overtop the rather patchy dunes which are our 'defence'. If the evidence of storm damage to the dune system over the last few years can be extrapolated, where significant erosion caused movement of dune sand out to sea (and, by happy coincidence, damaged beyond repair the startlingly ugly post and plastic netting fences to such an extent that they were later removed), a plausible effect of the many-orders-of-magnitude more damaging tsunami waves could be to erode and destroy the dune system entirely in the first series of waves, vegetative cover notwithstanding. Later waves (and tsunami rarely generate just one big wave) would then have no impediment. This effect would be particularly marked in the area of dunes with the narrowest base (and hence the least cross-section of sand to destroy). And where is this section of dune? From Shackleton Street to Waimairi Beach surf club - which contains the very area of L3 limitation already noted.

The notion of dunes as a 'crucial' element of defence nows seems rather tattered. The dune system is well overspecified for the Distant Tsunami's historical run-ups, which in any case cause markedly differing effects. Un-duned areas such as Central Brighton have not suffered historically. The Estuary, with known historical wave run-ups, is completely unprotected absent a barrage or other significant physical barrier at its mouth. Property along the south side of the Estuary and in any of the Peninsula Bays is at much more immediate tsunami risk than is New Brighton, because of the embayment effect. The jury is still out regarding the Southshore (Spit). And let's not even think about the non-notified consent for 14 storeys just along from Moncks Bay road....

And in a Near Tsunami, all bets are off. The combination of massive, energetic waves, short wave run time (and hence, little Civil Defence warning preparation time) and the probable irrelevance of the dune system (where it exists at all), means that the reasonable preparation via land use, dune retention and Civil Defence alluded to by the good Professor, will simply not cope. As Civil Defence staff will privately admit, the likelihood of evacuating in a planned, orderly fashion, the whole of the ocean-facing suburbs, across bridges which are few in number and may not by then exist, is close to zero for such an event. It would be intellectually more honest, and save a good deal of wasted or misdirected resources, if EC and CCC were simply to say that any extreme wave event cannot reasonably be mitigated in any way. As the call centre industry might say, it's YOYO support. You're On Your Own.

Rather than attempting to gauge and mitigate such an event, it would be a more productive exercise for EC and CCC to audit the Distant Tsunami effects, to a much better degree of consistency and clarity than currently appears to be the case. There are known risk areas (harbours, estuaries and bays) where warning systems, evacuation plans, and physical mitigation efforts such as a barrage could be considered.

The other aspect which should be considered is the adequacy of public and private provision of insurance for the respective facilities, services, dwellings and shops. After all, in an extreme tsunami event, it's not CCC or EC which, or private individuals who, end up paying out the bulk of the restoration costs. It's not AMI or State or FMG, either. It's Munich Re, Swiss Re, General Re: the re-insurers of the world. But this can only happen if there is proper cover, frequent physical audits and assessments of risk, and (of course) payment of premiums. I know how my own house is covered. Can CCC and EC say the same about their bridges, sewage pumps, and other infrastructure items?

There is of course a nice, simple, win-win which both ECan and City Council could support: creation of a reef system out in the bay. Wins: surfers get a decent break to ride, tsunami energy is dissipated by offshore reefs, and the reefs will attract and retain at least some sand from the Pegasus Bay longshore drift, thus delaying some decreases in Estuary depth.

So the present state of play over New Brighton Revitalisation can be summarised:

1. The present dune height over the Shackleton Street to Waimairi Surf Club stretch averages 8 metres (allegedly) or is absent (Central Brighton carparks, opposite the Ozone).
2. The L3 building height is limited to 3 storeys/10m as of right
3. A third floor apartment dweller would have only a marginal chance of a sea view (that chance depends on just which dune you're opposite, and on whether or not you have a kitchen table to stand upon). First and second floor dwellers - no chance.
4. So naturally the market for 3-storey apartments is, shall we say, nascent
5. Consents for higher buildings won't be granted case by case - a District Scheme Change is the preferred course of action
6. This will take years, allowing for submissions, objections, notifications, appeals and lawyers' retirement funds.
7. So if you've just spent several million dollars on beachside sections in anticipation of a consent as per 5), better tell your banker you're in for a long, rough ride.
8. And because some rather junky science is being quoted to defend the tattered state and average height of the coastal dune system (as adjudicated by EC), don't expect dunes to be lowered much, or soon, either.
9. Bingo! Catch-22 applies.
10. But the Council will cheerfully insist to all comers that it has a viable 'New Brighton Revitalisation Plan' in action, and point to all those buskers.

In his article, Prof Kirk alludes to the 'derision' with which at least some people greet the current dunes height policy. Perhaps now, we can see why.