Malborough flood response

Wairau River and SH6 looking towards Renwick. Photo: Marlborough District Council

The New Zealand climate is changing, which presents a new uncertainty in defining the standard of flood control works into the future for all over New Zealand. The Marlborough floods are just one to mention this year with the West Coast and South Canterbury floods creating havoc.

I expect more to hit us in the future, which will put a lot of pressure on local councils to assess and work on preventing rivers blowing out stop banks when the next flood hits.

One of the issues I’ve seen firsthand is in some areas on farms here in Marlborough the rivers/streams are filled up with sediment that has come down in the big flood which lifts the water level.

It takes less rainfall in these areas to do the same amount of damage, causing doubt and frustration among the landowners that boundary these water catchments. Do they change their fence lines completely and lose land, or do something more temporary?

The early vineyard developers got away with a lot more by changing small water catchments’ direction to get more grapes in and pulling trees out to archive the same thing.

Mike Renner and daughter Elloise with the Awatere River and SH1 behind them

Over the last 15 years we have learned from these select few the damage that can be done if you muck around with nature without researching the land first.

The last big flood we got in Marlborough in my time was the July 1983 Wairau flood, which was the largest known flood since at least 1868. There was recorded water flow of 5,800m³/sec. In July 2021 the river levels jumped, and officials said it was the largest ever recorded flood in the region. The Wairau River at Barnetts Bank reached 8.946 metres and a peak flow of 6040m³/sec.

As many as 900 people were evacuated from over 500 properties across Marlborough, including in the areas of Renwick, Spring Creek and Tuamarina, where 5 people were rescued from two vehicles caught in the floodwaters.

The phone has started to ring, booking in work after the tidy up has been done, which adds to the workload but must be done so the farmers can manage livestock with lambing beginning and about to start in other areas.

There was 300mm of rain in 48 hours recorded in some areas which has also caused large slips. The Awatere Valley road was blocked off above Awapiri Station leaving Camden Station and above blocked off. Locals had a car/truck on both sides to get bare essentials until the road was opened.

Renner Fencing have pushed some jobs back to make way for urgent flood damage work already, ranging from some temporary fencing until digger work has been done, to more permanent fencing ranging from 2 wire electric to 7 wire fences.

The force of the rivers has done a lot of scouring of the riverbanks causing the fences to hang in the wind – or they’ve completely disappeared.

It’s not just the fences that need sorting in the vineyard blocks. The loss of land from the river’s water force has taken away vital headlands that these days need to be 10-12 metres for safe turning space.

We have several blocks where the vineyard rows need shortening to make the headlands wider again, which involves cutting 7 wires on average and pulling old strainers and stays out. Most vineyards replace materials with a new strainer and stay plus blocks. Once strainers and stays are in their new position the painful job of re-straining up all the wires to desired tension begins. Depending on how many rows are affected this can take up most of the time on the job – but it’s good practice for a learner to tie termination knots.

Mike Renner