Welcome to Thorrington, a charming suburb of Christchurch that sits at the foot of Dyers Pass Rd, in a loop of the Heathcote River sandwiched between Somerfield, Beckenham and Cashmere. In fact its not really a suburb, unless three streets encompassing four small blocks of residential houses, plus a primary school and a few shops equals a suburb. It doesn't even appear on some maps, although it does have a postcode. Annoyingly, some of us have to constantly spell not just the name of the suburb but the name of their street as well (Wherstead Road) or the pizza doesn't arrive. It's actually quite easy to find, but just as easy to drive past in less than a minute.
However, since February 22nd our little patch has appeared on a very different map, one tinted in shades of red like a spill of wine. Provided by the French National Centre for Space Studies (CNES), this satellite photo shows in some detail the extent of flooding and liquefaction throughout Christchurch shortly after the February 22nd event. We're still hard to spot, a small blob amongst larger areas scattered around the Heathcote Valley, a tiny dot in comparison to the stricken Sydenham and Woolston areas, a pinhead next to the devastation of the twice-hit northeastern suburbs.
To get a real perspective on the scale of things, click the photo to view the full zoomable map (Ctrl +/-) in a new browser window. Click right on the map to save a copy directly to your computer.
So, where do we stand when it comes to an assessment of our local problem, the likely cause and future risks, or proposals that may affect any claim already in progress? Is there a worst-case scenario that we should know of, sooner rather than later? Given the probability of another event, does it make sense to attempt land and property remediation, only to be shunted back to square one before current claims are resolved? Liquefaction and underground water takes no account of fences or boundaries, so it would seem logical to have direct dialogue on specific land issues at community level. Without knowing what lies under our feet, any other decisions regarding individual claims will be tentative at best, highly doubtful at worst.
The map at right shows sites in the Thorrington area where several types of geotechnical tests have recently been carried out, clearly indicating there is a known issue with the land beneath. The line in blue (added) corresponds with evidence of subsidence and a large amount of liquefaction, affecting many properties in Thorrington Road and almost all of Wherstead Road. Evidence of a pocket of high water pressure at a depth of about 11metres, the existence of an underground spring in Ernlea Terrace, as well as the historical Black Map, all suggest an aquifer or artesian water system may be present.
Click right and choose "Save link as" to download in .pdf format. For further interest, EQViewer gives another aerial perspective of the extent of damage shortly after February 22nd. Confirmation the area is in a high-risk category is shown in the ECan Report of September 2010.
With so many organizations already involved in the recovery and claims process, and the sheer scale of geotechnical assessments, essential information will most likely be slow in coming. Tonkin & Taylor are somewhere in the middle of the administrative tree, contractor to EQC and sub-contracting a range of specialist technical services. With these arrangements results of tests remain proprietary, even though reports in some form are ultimately destined to be made public. Whether organized community groups such as the proposed Thorrington Earthquake Recovery Association can change this is uncertain, though results of initial requests for information have not been entirely negative.
Well-publicised deadlines for the release of a new series of initial reports following the February event have already passed by. If a specific problem has been identified in a small area such as Thorrington, it would be reasonable
to expect quick access to any information that will aid the resolution of claims. By establishing a community group such as the TERA it is hoped that ongoing communication will be maintained on this issue and more, rather than relying solely on official arrangements to produce results.
Matt Morley
5A Wherstead Road