Could a flood this bad happen again?

07:05, Mar 04 2009

It's easy to use extravagant language to describe the floods of 1984.

Even in Southland, where constant rainfall is a fact of life and evacuations in Gore, Mataura and Wyndham became almost routine between 1968 and 1980, the January 1984 floods were on a scale all of their own.

The rainfall recorder at the Invercargill airport showed a mammoth 134mm of rain fell there in the 24 hours to 9am on January 27. The previous daily maximum was 73mm. In the scale of large floods, this one was reckoned to be a "1000-year flood".

Could it happen again? Certainly.

The MetService issues heavy rain alerts for Southland every few weeks and given the right circumstances steady rain, a slow-moving front, saturated ground there is no doubt we will see major floods in Southland again.

Environment Southland's catchment manager, Noel Hinton, says Southland has simply been lucky to miss most of the foul weather systems that have dumped torrential rain on other parts of New Zealand in the past 20 years. "We had our turn for floods from 1968 through to the late 80s and other regions have been having their turn in the meantime. But all it needs is one of these fronts to slow down or turn round and come back and it'll be our turn again."


The difference is that Invercargill City, Otautau and Tuatapere are now protected by flood schemes designed to contain a 1984-size flood with half a metre to spare before water flows over the banks. Gore, Mataura and Wyndham are protected against an October 1978-sized flood, the largest yet recorded on that river. The Invercargill City Council also upgraded most of the city's drainage system after 1984.

The calls for flood protection came within weeks of the floodwaters subsiding.

The Invercargill City Council formally asked the Southland Catchment Board to design comprehensive flood protection schemes on the Waihopai River and the Kingswell Creek to a standard that would prevent a recurrence of the 1984 flood. The Wallace County Council sought the same for the Aparima River and the Otautau Stream to protect Otautau, and the Waiau River upstream of Tuatapere.

Ironically, a scheme for the Otepuni Creek had already been drawn up by the board and was awaiting ICC consideration when the floods struck, while a comprehensive scheme for the Lower Oreti River that would have saved the Invercargill airport was stalled for want of government approval.

The National Water and Soil Conservation Authority and the Treasury had to authorise all major capital expenditure.

The schemes were designed by the Catchment Board, endorsed by the Invercargill, Southland and Wallace councils then sent to Wellington for approval, where they disappeared for nearly three years.

It took another flood to clear the bureaucratic blockage.

In March 1987 heavy rainfall led to widespread flooding and a state of emergency was declared over the whole of Southland region except Bluff.

Rural areas were badly hit, the Invercargill airport was swamped again, many city householders lifted their carpets and prayed; but Otautau was worst affected, with 700 people evacuated.

When Works Minister Fraser Colman and Civil Defence Minister Peter Tapsell visited to inspect the damage they were met by 300 angry locals outside the Wallace County offices complete with a hangman's noose lowered from the veranda wanting to know why the flood schemes had not been approved.

Noel Hinton remembers the frustration catchment board engineers felt, knowing that the schemes they had designed would have prevented most of the flooding in 1987.

"It gave impetus to grab ministers by the scruff of the neck and hold them up in front of the citizens and say: `now look us in the eye and tell us that we can't get any money'."

Part of the problem was the rate of economic return that schemes had to provide on any government funding.

Despite the huge losses from the 1984 floods estimated at more than $100 million, with half of that incurred in Invercargill officials disputed that the schemes would provide the required level of benefit.

The March 1987 floods brought the proof of that. The next problem was how the communities were going to pay their share of the multimillion-dollar schemes.

In April 1987 Southland's mayors and MPs flew to Wellington to lobby Finance Minister Roger Douglas for an increase in the level of government subsidy available and quick approval so that construction could get under way.

They came home with the promise of a 70 per cent subsidy for the $4.9 million total cost of the Aparima, lower Oreti and Kingswell Creek schemes.

The Otepuni scheme was approved separately, and signoff for the $9.5 million Waihopai scheme came last of all, its subsidy tagged with a proviso that the work had to be completed by the end of March 1992, or the subsidy rate would halve from 70 per cent to 35 per cent.

Diggers, dozers and dumptrucks were busy for the next five or six years, constructing the schemes that have become a part of Southland's landscape and, since they were completed, the stopbanks, culverts and detention dams haven't really been tested.

Environment Southland maintains the flood protection works, in the sure knowledge that one day could be any day now that heavy rain will start to fall again.

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