The value of braiding to the Wairarapa’s rivers

David Famularo, March 2016

An example of braiding on the Waingawa River
An example of braiding on the Waingawa River
An example of channelling of the Waingawa River
An example of channelling of the Waingawa River

After writing a Letter to the Editor of the Wairarapa Times Age in regards to the negative environmental impact of erosion and flood protection work on the Wairarapa’s major rivers, I was visited by a gentleman who was very closely involved with river management in the Wairarapa from 1985 to 2005.

While he didn’t want to be named for a story he expressed his views on some of the impacts of this work, especially the bulldozers in the river itself.

While the river work often involves creating artificial channels for the rivers, he emphasised the importance of the rivers, especially the Waingawa being braided and containing natural obstacles such as the islands that were removed back in the 1990s.

“You see the meandering patterns migrate up and down the river naturally over a six month period. The more braiding and metal you have in a river, the more energy it takes out of the flow.”

He recalled that in the past when the rivers flooded they simply overflowed their banks and then receded back to their natural course without eroding the river banks.

Whereas today with the faster flow of rivers in flood due to channelling, these are consuming the river banks. “The rivers have got a lot of energy in them which causes the bank to erode.”

Aquatic life is suffering from the bulldozing, he pointed out, with the loss of small and large rocks, and the destruction of the natural sequence of pools, runs, riffles, pools, runs riffles etc.

But the disturbance of the river bed is having other effects as well, with the loss downstream of the small particles between the larger stones. This is causing water to be lost underground.

Furthermore, all this loosened metal is carried further downstream, ironically creating potential flood hazards further along the rivers.

He cites one particular example that he knows well as being the lower reaches of the Tauherenikau River, prior to entering Lake Wairarapa, where metal is building up.

He points out that along the river at this point, the “diversion” road that runs along its eastern edge is actually lower than the river itself.

“If the stop bank there was busted it would inundate a lot of farm land. It would only take a small hole in the bank like a rabbit burrow, or the river topping the stop bank. Once topped, the water would quickly scour the breach and make it larger with a lot of metal going on to farm land.”

This story from the Tasmanian Times does a very good job of giving a general outline of what current river management river practices are doing to the Wairarapa’s rivers here.