Counting the costs of flooding
The Rangitata River floods caused significant damage in December last year, flooding homes and properties, cutting access across the river at SH1 and SH79 and wiping out the rail corridor, effectively cutting the South Island in two. Travellers were stranded either side, telecommunications were cut, power was cut, freight was unable to get through in the lead up to the busy Christmas period. Reporter Matthew Littlewood looks back at the impact and counts the costs a year on.
It all started with a lot of rain. And it is still costing money 12 months later. On December 6, 2019, the Rangitata River was in raging flood from record rainfalls in the Southern Alps and broke out of its main channel at three key locations during an extreme weather event that hit the West Coast and Canterbury.
The storm brought six days of heavy rain, causing three high flows in that river that peaked at a massive 2307 cumecs, more than 35 times its usual flow and effectively cut off the bottom of the South Island as highways and rail links were closed for several days across the Rangitata along with the Haast Pass (SH 6) on the West Coast.
Rainfall stations at Mistake Flats and Erewhon, near the headwaters of the river, recorded 930.5 millimetres and 424.5mm respectively from December 1 to December 9.
It was, according to experts, a one-in-20 year flooding event, and the river’s break out sent water down its normally dry south branch for the first time in 24 years.
The damage to flood protection, roading, rail, farm, electricity supply and other assets was significant and is still causing issues for Environment Canterbury and other organisations as they work through repairs.
Even The Timaru Herald was affected by the floods. The paper is usually printed in Christchurch and transported south each day, but this was not an option at the height of the floods, meaning the December 9, 2019 edition, was printed in Dunedin.
The floods were so severe the Timaru District Council declared a State of Emergency that lasted almost a week. The roading situation was dire, with flooding closing State Highway 79 (Dec 7-11) and SH1 (Dec 7-11).
Problems were compounded when Spark’s landline, broadband and mobile services shut down
cutting phone connections to many in the lower South Island. Eftpos was also affected, leaving some businesses in Timaru and Geraldine and further afield unable to take card transactions and people queueing at ATM machines to get cash.
With the South Island effectively cut off, scores of people were forced to sit out the flooding at motels and holiday parks, particularly in Geraldine, while in Timaru dozens of tourists were among at least 80 people forced to find shelter through the Southern Trust Event Centre, which Civil Defence used as a base to help stranded people. There were even reports of panic buying at Timaru’s supermarkets and bakeries.
Some Rangitata Village residents reported their homes were flooded three times in as many days. Rob Wilson, who runs a farm near the south side of the Rangitata River, said the damage was ‘‘devastating’’.
‘‘Two of the breaches came right through the middle of the farm,’’ Wilson said.
‘‘At the time, there was huge damage to irrigation infrastructure, while it was a challenge moving all the people and animals to safety.
‘‘There was so much support from the community and from contractors, we were also warned in advance that a big flood was likely. We just didn’t know how big.’’
Wilson, whose farm business near the Rangitata River employs more than 25 people, said the flooding was a particularly trying time.
‘‘At the time, you’re all operating on adrenalin, but the cleanup can take weeks or even months.
‘‘We were fortunate not to lose any animals.’’
Wilson said the sight of a power pylon collapsing across his property was a reminder of the sheer destructiveness of the flood.
‘‘It was just so hard to believe until you saw it,’’ he said.
Even now, there is considerable infrastructure spending required on the Rangitata River.
ECan river engineer Leah Griffiths said new flood protection, erosion control infrastructure, and tree planting are required.
The initial emergency repair works were completed between December 2019 and February 2020 at a cost of $770,000.
Funding of these works was split between Environment Canterbury (through the Rangitata River Rating District), Waka Kotahi NZ Transport Agency, Kiwirail, Rangitata South Irrigation Ltd, Ashburton District Council and Transpower.
‘‘Upcoming flood recovery work will be completed in stages,’’ she said.
‘‘The next stage of works will focus on urgent repairs to restore flood and erosion protection measures for the community. The works programme will likely cost $2.5 to $3 million. It is anticipated that this work will begin in early 2021.’’
Griffiths said further physical works were likely, although the detail of these works has not yet been scoped.
‘‘This is a unique opportunity to accelerate regeneration of the natural environment, engage with communities, partner with mana whenua and other stakeholder groups and lead the way for climate change resilience,’’ she said.
‘‘Following this, and in partnership with Arowhenua ru¯ nanga, we will be commencing further investigations to support a holistic vision for the river, inclusive of the south branch, with opportunities for biodiversity and mahinga kai enhancements.’’
Nine of Transpower’s transmission towers in a threekilometre section of its high-voltage Roxburgh to Islington line were damaged.
Transpower’s general manager grid delivery Mark Ryall said this resulted in the loss of one circuit supplying the upper South Island.
‘‘Despite this, there was no loss of power to communities, as Transpower was able to redirect supply via other circuits,’’ Ryall said.
He said the design and construction of both temporary concrete pole line, permanent new tower line and dismantling of the temporary line (three-kilometre section), excluding the initial fault response and clean-up, totalled about $6m.
‘‘Repairing the National Grid after the Rangitata River flood certainly had its complexities.’’
He said the response over the months following was twofold: a short-term restoration to ensure the resilience of the national grid during the winter months, and a permanent solution.
Construction of the temporary pole line began in February and was commissioned (or made live) in late March.
The permanent new tower rebuild was completed and commissioned at the end of August.
The new foundation called for piles 18 metres in length to be driven in and encased in concrete. Concrete encasement is from 10 metres below normal river height to three metres above normal river height, where a large new concrete plinth ties the four legs of the tower together.
Despite the work, Ryall was realistic about the possibility of the river flooding again.
‘‘Risk from variable flows in the beautiful braided Rangitata River remains a constant threat.’’
Kiwirail South Island general manager Mark Heissenbuttel said around 330 metres of the Main South Line suffered significant washout damage.
‘‘The total cost of repairs to reinstate the section of damaged line at Rangitata was $1m,’’ Heissenbuttel said.
‘‘The cost of remediation reflects the degree of damage and the significant repairs our staff and supporting contractors carried out on the affected section of line. In one area, part of the track formation, which supports the track surface, was eroded to a depth of five metres.
‘‘Weather events can be challenging because the repair work itself is weather dependent. For this event, the waters needed to recede before the repairs could start, as the flood waters were so high.’’
There were also serious issues for roading, with the SH1 and SH79 flood repairs costing Waka Kotahi NZ Transport Agency $1.3m.
Waka Kotahi NZTA maintenance contract manager John Keenan said almost a year on its repair work is largely complete, with ‘‘just a small area of SH1 that was flood damaged on Rangitata Island which has slumped a little’’ to be remediated and resealed soon.
‘‘A major obstacle, which caused delays at SH1 Rangitata, was repairing the stopbank breaches to stop flood water that had broken out from the main river channel impacting upon the main trunk rail wash out and the flooding over/on top of SH1 so that repairs and road opening could be accomplished.’’
Insurance Council New Zealand (ICNZ) chief executive Tim Grafton said events such as the floods reinforce the need for insurance.
While the ICNZ could not give a breakdown of claims for the Rangitata flood, the total claims for the South Island storm events from December 3 to 18, 2019, amounted to about $15m.
‘‘Sadly, extreme weather events are becoming ever more frequent and severe for our communities, and we know that with climate change this will only increase,’’ Grafton said.
‘‘It is clear that we need to adapt to the changes we are seeing and take steps to reduce risks where possible to minimise the social impact and cost to our communities.’’
‘‘At the time, you’re all operating on adrenalin, but the cleanup can take weeks or even months.’’ Rob Wilson, Rangitata Village resident