Flood Impacts

Big job ahead for watertrampled vineyards

SOPHIE PREECE

THE STOP bank at Bandillero I vineyard in the Wairau Valley has done its job for 20 years, keeping the river out of its rows. But when 6,000 cumecs of water tore down the Wairau River in mid-July, 100 metres of the safeguard failed, allowing flood waters, sediment and forestry waste to charge through the vines. “Basically, the water came in with all of its trash and everything it had with it,” says vineyard manager Dominic Pecchenino, equating 6,000 cumecs with 6,000 tonnes per second hitting the stop bank.

In the water’s wake, the vineyard was left a “mess”, with posts, vines and wires gone in a small portion of the block, and a bigger area hit by debris along the vines and sediment underfoot, which will also require a clean-up. Dominic says that work is intensive and “hands-on”, at a time when labour is already scarce.

The flood was reportedly the biggest ever recorded in Marlborough (see Flood Plains sidebox), and saw a State of Emergency declared on July 17, and in place until July 28.

Wine Marlborough general manager Marcus Pickens says it appears most of the region’s vineyard area got through the event unscathed, despite images that show large tracts of vineyards submerged. “In many cases the water pooled and then dispersed just as quickly,” he says. However, a journey around vineyards five days after the flood, when Minister of Agriculture Damien O’Connor visited the region, revealed the more severe impacts being faced by some growers, Marcus says. “There are some people grappling with clearing, repairing, replanting and rebuilding infrastructure, just when they need to focus on the business of pruning.”

Dominic says the energy of the river caused it to change direction, so it hit the stop bank head on. That is both the beauty and the problem with braided rivers, he says. “Every flood the river changes a little bit… It just so happened that the main flow of the river actually turned into my stop bank.”

At the time of writing, Dominic was assessing the cleanup of the vineyard and restoration of the stop bank, which was built in 2001. “I have a lot of work to do. It’s a matter of getting it done on time and making sure we are ready to go.” He is gutted, but philosophical about being hit by such a rare event. “I know what I gotta do and I know what is ahead of me,” he says. “We have been farming there for 21 years and never had any damage.”

Over in the Waihopai Valley, Leefield Station suffered serious damage to some lower terraces, after the Waihopai River swiftly changed course, tearing through a 10 to 15-hectare block of young vines. Owner Brent Marris says the area had yet to have trellis and posts installed, and he is certain the whole lot would have been washed out had that infrastructure been in place.

The river had suddenly moved from flowing eastwest to flowing south-north when it jumped its banks, says Brent, considering it a saving grace that it ran in the same direction as vineyard rows beyond that young block, rather than across them. So, while they still have debris to clear from the canopy, “it could have been a hell of a lot worse”, he says. “We probably got off rather lightly when water flowed through the vineyard. But we had an area quite substantially gouged out and we’ll have to reinstate that.” The flood also knocked out the water main servicing the whole of Leefield Station.

Brent says the change was very rapid, noting that over at Marisco’s Waihopai Vineyard, which lies to the north and within view of Leefield Station, a crew was moving his mobile River Hut from the edge of the Waihopai. “The guys were ankle deep in the process of towing it out, and within 10 to 15 minutes they were thigh deep.” On that site, the damage was negligible once the river route was restored and the water receded. “Just 24 hours later, when the river was back within the banks, you would have thought the lawns had just been mowed. It was absolutely incredible,” he says.

Back at Leefield, bulldozers arrived by the end of the week, pushed the stones up and redirected the water back to the channel. “The next process for us is reinstating the water mains and land we’ve lost, then replanting the vines. We will also be constructing a stop bank,” says Brent. The company, which has been at pains to future proof for climate change, had already been in the process of river retention work, “chipping away at self-management and controlling our destiny”, says Brent. “But the size of this change in water flow did catch us unawares and shows you how strong nature can be, when it deals its hand.”

Haysley MacDonald grew up knowing how strong nature can be, and when floods threatened the family’s Lower Wairau property, they would head to higher ground. But he’s never seen anything like the impact of the July floods, which saw raging waters top the stop bank and flood his te Pā vineyards, leaving deep layers of silt and waste wood among 20 to 30ha of vines, as well as posts broken by floating logs. “It’s fair to say a big chunk of that will come from forestry,” says Haysley, frustrated that a vineyard neighbouring the ocean has been struck by logs, branches, roots and sediment washed down from distant hills. “Water we can handle. It’s the crap that comes with it - the logs, the slash and the sedimentation- that’s what kills it.”

As soon as they were able, Haysley’s crews started pumping out the water, night and day, then started the task of clearing the detritus from the vines, which reached the fruiting zone, indicating the height of the flood waters. “It’s a hell of a mess and particularly in some places,” says Haysley, who has teams using stripping machines to lift the wires and clear them out. “It’s a bloody nightmare.” Meanwhile, the sediment, which in some cases is above the 30cm irrigation wire, will likely have to be worked into the ground.

“I have been brought up with the floods all my life,” says Haysley. “But this time it was close to breaching the banks.” He wants the Marlborough District Council to spend more time and money at the Wairau Bar, ensuring the flow of flood waters to the ocean isn’t impeded. “It’s getting better, but still not enough.”

Rose Family Estate had a veritable lake form on one of its new vineyard developments between Hillocks Rd and SH1, with water up to post height. But chief executive Lindsay Parkinson says the vineyard flooding was a result of water “gently banked up from the Spring Creek side”, rather than the “raging torrent” of the Wairau River. It rapidly drained away over the next few days, leaving very little damage, if any, in its wake.

The estate’s home vineyards on Giffords Rd escaped the flood unscathed, although there was a tense wait to see if the water would breach the Wairau River stop bank. Lindsay says for the Rose family, including his wife Pip and parents in law Phil and Chris Rose – founders of Wairau River Wines – the flood bought back “pretty fresh” memories of 1983, when they were forced to evacuate their Rapaura homes as the waters breached the river protection.

Damian Martin, science group leader - viticulture and oenology - at Plant & Food Research, says wet conditions can increase the risk of root disease like blackfoot, but the vines themselves can survive being under water for three to four weeks in winter. “In the old days in Europe people would flood vineyards if they could, to kill phylloxera,” he adds. “So, they can sustain quite a lot of time under water.”

Viticulturist Ivan Sutherland cannot “foresee any major problems” in Marlborough’s wine industry as a result of the recent floods. “Grapes can withstand wet conditions, particularly in winter when they are in dormancy for a while,” he says, noting that as long as the water clears relatively quickly, the vines prove impervious. Ivan, coowner of Dog Point Vineyards, has seen a multitude of climatic conditions over the past four decades growing grapes in Marlborough, including the 1983 flood. “I have seen vines immersed in water before,” he says.

The Marlborough District Council has done an “excellent job” of flood protection works, which proved their worth during the recent emergency event, he adds. “It was great to see how the main stop banks held.”

However, in recent years the wine industry has “pushed the boundaries” in terms of Marlborough’s plantable area, with vineyards “right up the valley and by the river”, he says. “So, you would have to expect that there’s an extra added risk in terms of climate – whether that’s floods or frosts.”

The Wairau River at State Highway 1, with the Wairau Diversion going off to the left, Lower Wairau to the right, Morrins Hollow floodway area centre top, and Spring Creek township top right. Photo Peter Hamill/MDC

Flood Plains

Last month’s flood, while dramatic and destructive in some areas, seems only “marginally bigger” than the 1983 Wairau flood, says Marlborough District Council hydrologist Val Wadsworth, who is awaiting “the final numbers”. In 1983 the flood breached the stop banks at Conders Bend, freeing the flow into the Renwick lower terraces, and also broke banks at Tua Marina, where it flooded the township, and at the State Highway 1 bridge, flowing south through Spring Creek township and into the Grovetown and Jones Rd area.

No one knows how July’s flood compares to the 1868 and 1923 Wairau floods, before formal records or stop banks, but in 1868 ‘“a gentleman from the country” reported to the Marlborough Express looking down from above Blenheim to see what seemed “one vast sheet of water”, says Val.

The July 2021 storm event resulted largely from northerly rain in the Richmond Range, filling tributaries on the Northbank from the Waikākaho to the Goulter river. In 48 hours, the hills received a total of more than 325mm. However, Val says the more pertinent timeframe for a Wairau flood is peak rainfall within a nine to 12 hour period, and from the evening of July 16 to the morning of July 17, the Richmond Range received around 16mm an hour for 11 hours.

That saw the river levels rise to around 6,000 cubic metres per second (cumecs), but the flood was “well contained” within the council’s own flood bank system, which extends from the Waihopai down to Cloudy Bay, he says. That’s despite the stop bank network containing 10% more volume of water in the flood than its design capacity of 5,500 cumecs.

The flow did overtop the banks in some places and there were a couple of breaches, where the bank broke, he adds. “Whenever you get a flood that big it may find a weak point.” There was also a “big boil hole” at Morrins Hollow near Spring Creek, where the water was tracking down under the stop bank and eroding on the other side, he says. “It put a lot of water through that boil hole but the bank didn’t actually breach.”

Many of the damaged areas are within the 50 year flood hazard zone, Val notes. “Much of the land planted in grapes in the Wairau Valley was riverbed when I was a kid.”