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Christchurch is a water city like Venice

kenring March 6, 2014, 3:32 pm

Estimates vary as to how much the city floor has lowered, but it seems to be between 30cms and over a metre. It means that what were ancient waterways and escape routes to the sea for run-off water from the hills and plains will be so again and any decent amounts of rain around close perigees (closer moon distances per month) is likely to bring flooding now to Christchurch.

Those living in low-lying locations must prepare for the next round of equal amounts of flooding in late July because that is the next highest kingtide due to a close perigee and time of expected heavy rains in the region. After that the next biggest calamity may be in the third week of March 2015.

But in the interim the situation does not look too healthy. We have just been through the second highest tide of the year (2-3 March) due to perigee #6. It has also been the 4th highest kingtide out of the top 50 kingtides between 2010 and 2015. Looking ahead, the next heavy rain for Christchurch is likely around the middle of March, followed by rain about 17 April which is the start of Easter. Kingtide then will not be as high as this recent kingtide, but may still cause some flooding.

10 May brings chance of a heavy rain dump that should clear quickly but rains 27-31 May are again potential flood days due to high tides. 22 June may bring heavy rain but quick to subside. The 12 July brings both rain and snow and lesser kingtide but still some chances of flooding, and then 22-28 July again brings much rain to the region as well as snow flurries, with a significant kingtide 3 days later and for this event dire flood warnings may be again issued. Then 6 August may bring more heavy rain which may again clear quickly due to lower tide levels.

Around 1 September between Hanmer and Ashburton we can expect some heavy falls, but September, October and November should be relatively dry months, enabling much in the way of cleanup operations. Then the next expected heavy rain is around 16 December, which may be the wettest spell for Canterbury’s very dry spring.

In 2015, 10-15 January brings at least 2 heavy rain days and 21-22 January brings possible rain across the whole South Island, with a very high tide once again, due to perigee#6 (the same perigee distance as in recent days). The next heavy rain date is 15-16 February but tides are lower. Then the 16-22 March 2015 is looking to be extremely wet with a huge kingtide repeat, and this flooding event may be equal to what is happening now.

As well as water tables currently at higher levels than pre-2010, liquefaction has raised closer to the surface rather being at depths. Christchurch will get waterlogged faster than it used to do because it can no longer utilise the filtering system that was there before. What is needed is a massive dredging of the Estuary, for all rivers empty into it. If the Estuary is not free running then everything else gets blocked.
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It would seem that all rebuilding needs to stop immediately and reconstruction be diverted to dredging operations, enabling the removal of water quickly from residential streets and out to sea, aided by large channels between roads and properties. Perhaps the army needs to be involved as if it is an invasion, which it is - an invasion of water. There is currently a greater requirement for fixed homes than for a shiny new convention centre facility for events no one can afford to attend.

A sunken city is not a temporary setback. Those who cannot move need to at least relocate water-damageable valuables and furnishings to upper floors or elevated levels at least a metre up from the floor, in readiness for living with regular flooding risks to come. Beds need to be raised bunk-style off the floor. What is again needed is an action group mentality to help families to work positively through options.

Earthquakes come and then subside, but the water table is here to stay. Nature is returning Christchurch to the swamp that prompted Captain Cook to name Banks Island. The great navigator would have sailed around Banks Island as all cartographers were required to do before finally naming an island rather than calling it a peninsular. Cook visited NZ three times and sailed five times along the South Island east coast. In the 1830s Banks Island was the hub of the whaling industry and by 1849, 1000 people lived in the district, mainly on Banks Island..

On April 20 1848 Captain Joseph Thomas arrived at Lyttelton, having been commissioned to choose a site for the New colony and make necessary preparations for the arrival of settlers in 1850. In a letter to Governor Sir George Grey, Thomas revealed that he had chosen the present site of Christchurch for the new settlement - in spite of the fact that both Nelson and Otago colonists had rejected it in 1841 and 1844 respectively. Even then there was disquiet over the choice of location
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This is Election year and will be a golden opportunity to quiz parliamentary candidates as to where they stand on prioritising the needs of Christchurch flood and earthquake victims. The region does not need visible displays of generosity to attract votes. Until wide scale reclamation works are underway it will be tough for all families. Let us hope that wiser and more compassionate heads might prevail than we have witnessed over the past three years, and speedier relief programmes. Otherwise we have learned nothing. What must now be faced is that the city is now a water city, like Venice.

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