The Waihao Box Celebrates Centenary

It’s the only functioning one of its kind in New Zealand, if not anywhere in the world, and this year the Waihao Box is celebrating its 100th birthday.
“The Box” is well known to many South Canterbury residents but mention of it can prompt looks of bewilderment from anyone else. Is it a prison? A sporting event?

The Waihao Box, in the Waimate district, is in fact a simple but none-the-less ingenious structure that helps create an opening through the gravel beach to the sea for the Waihao River. It has proved vital in preventing flooding over tens of thousands of hectares of valuable farmland and helps maintain the health of a natural wildlife habitat of national importance.

The Wainono Lagoon and the beach that separates it from the Pacific Ocean are typical of Canterbury’s coastal landforms with their long sweeps of gravel beaches, ever-shifting river mouths and lagoons that usually open to the sea only in times of heavy flooding. Ocean currents are constantly moving gravels and sand northwards along the Canterbury coast but at the same time, a decrease in larger sediment due to the Waitaki River and basin hydro schemes has concentrated the sea’s energies more on the beaches themselves leading to erosion of up to 0.5metres a year. The result of both these processes is a dynamic ever-changing coastline.

Before the land was settled by Europeans in the 19th century any flooding across the low-lying land that surrounded the Waihao River and the related Wainono Lagoon and wider catchment area was simply nature at work. But, since then about 2500ha of fertile, very valuable farmland has been developed in the Wainono catchment. Flooding, as a result of the outflow from the lagoon and its river systems not being able to break through the gravel barrier to the sea, became a serious economic hazard, as well as risk to the safety of residents, visitors and livestock. It was even noted in a local family chronicle of the late 1890s that land in the area was selling at about 20 pounds an acre and could be even higher if they could stop the flooding.

More than 100 years ago those early settlers, possibly using a technique that they’d used or seen in operation in Great Britain, decided to tackle the problem. In 1896 they built the forerunner of the current box.

But how did it, and its current replacement, actually work? Simply, the Waihao Box is a long, rectangular, mostly wooden structure that links the river with the sea. However, it is not a culvert or a pipe. Water can flow through the box but what is especially ingenious about it is that the north-facing side of the box is open so that when flows are especially heavy pressure builds up in the box, so that water is then forced out the open side thus speeding up erosion of the gravels alongside it. These then scour away creating a channel from the lagoon to the sea. There’s a “nose” at the sea-side end that helps prevent the sea washing into the box (and thus stopping river water flowing out).

It is believed that the Waihao Box is the only functioning one of its kind in New Zealand and possibly in the world. There were once two on Saltwater Creek near Timaru (one of which was still working until the 1970s) and one on Horseshoe Bend Creek (also in the Waimate District). Further afield there was thought to have once been a box on Lake Ellesmere near Christchurch and possibly two somewhere in the North Island.

Boxes are regularly subjected to remorseless pounding of heavy seas and need constant maintenance. One of the earliest reports of this being carried out at Waihao comes from 1898 when four men had been rowing back from carrying out repairs when their boat foundered. Thankfully all were rescued.

Unfortunately the box piles were not sunk deep enough into the shifting beach gravels and in 1908 during a severe storm and heavy flooding witnesses were perturbed to see the box being propelled end over end into the sea then floating away.

Local man Norman Hayman reported at the time: “the box broke up in 20-foot sections, sometimes with all the piles which were only 20-foot long, up in the air”.

During a flood in 1900 when there was no box in place men in three teams using scoops and shovels spent six hours trying to dig out a narrow channel to release the water. It was back-breaking work. So, by 1910 local land-owners had resolved to try again with a new box. They’d learnt from earlier mistakes and this time sunk the piles down about 10 metres into bedrock – more than three metres deeper than the first box.

This time they got it right because it’s this box that turns 100 this year. While some of the structure contains original timbers other parts are, as one local describes it: “a bit like Paddy’s axe”. Over the past century, as the sea wore and tore away sections of wood and even chewed away some of the bolts, there has had to be a great deal of maintenance carried out and replacement timbers used. Because the beach is eroding back, the box has had to migrate too – it’s been shortened on the sea-side three times since 1932 by more than 30 metres in total and lengthened on the lagoon side to compensate.

For about 70 per cent of the time the box stays closed, and is often covered in gravel, up to several metres deep at times. This helps protect the structure itself which is usually only exposed during heavy seas and when flooding occurs.
Donald Hayman, whose family farmed in the Wainono area for about 100 years has now retired to Timaru but had served for many years as the chairman of the Wainono Drainage Board. This was the era before Environment Canterbury took over the overall management of the Box in 1996.

Donald has vivid memories of the amount of time the locals spent helping to maintain the structure.

“When the sea conditions were right we’d work 12 hours non-stop because we had to make the most if as other times it was just too dangerous.

“It was the nose of the box that was most exposed to the sea so we concreted this and incorporated two old harrows. We tried all kinds of wood over the years…usually Australian hardwood but this seemed to pit badly. We’ve even used pine on the top where the sea has less impact and this has proved cheaper and works well. There’s no need to treat the wood because the sea water does this naturally. There’s also been poplar, radiata and oregon tried…we’d scavenge just about anything to keep the costs down.”

Donald says that even after years of maintaining the box the power of the sea still impressed him. “We’d use one and-a-half inch bolts and someone would have to get inside the box to tighten them with a 24-inch spanner. They’d keep bashing and tightening them but then sometimes after some heavy seas we’d go down there and the nuts would have completely gone.”
Mick Laming, the current chairman of the Wainono Drainage Scheme committee, says the 100-year-old box is just as pivotal to the protection of land now as it was a century ago. He too remembers the local working bees in the days prior to Environment Canterbury taking over when a heavy digger and volunteers armed with sledgehammers would make the most of a calm sea day to perform essential maintenance.
“We did receive a subsidy to help with the work but we did as much as we could ourselves to keep costs down.”
Over the decades various less labour-intensive and possibly cheaper alternatives to the box have been considered including pipes and even blasting out a channel.
“But after all these years no-one can come up with anything better than the box, so hats off to those early pioneers - it might be relatively expensive to maintain but we simply can’t afford not too now. We’ve had to increase the local contribution to its maintenance three times but with so much more irrigated land in the area the box is, if anything, even more important now,” says Mick.

Bruce Scarlett, Environment Canterbury’s Timaru-based Rivers Engineering Officer, says work on the box is now funded by a combination of contributions from local ratepayers (80 per cent), 15 per cent from Environment Canterbury’s Waimate District rating and 5 per cent from the overall Environment Canterbury rate from throughout Canterbury. Between $10,000 and $20,000 is spent on it annually but this can increase to up to $50,000 if a storm and or/heavy seas has inflicted major damage on it.

It’s considered not only a vital part of flood control in the area but, after a century in operation has become woven into the overall ecology of the river system providing a vital link between it and the open sea for whitebait, eels and other animal life.

The Waihao-Wainono is also very popular with boaties, jet-skiers and other recreational users and the picnic area near the box is always well used, especially in summer.

It’s not a place without its perils however. The gravels around the box are designed to become unstable in heavy seas or during flooding to encourage a channel to open and gravel slides are common. Tragically in 2000 a 14-year-old boy drowned beside the box after becoming trapped in the unstable stones. A simple plaque in the picnic area commemorates the teenager’s death with the words “May His Loss Remind Others of This Area’s Dangers”.

So, during its 100 years in existence the Box has had its share of heartbreak and drama but at the same time it’s become incorporated in the natural rhythms of the river ecosystem and contributed to the economic and social wellbeing of the district by reducing the risks of flooding and to the recreational opportunities of the entire district.

Mick Laming believes that, possibly because of the position of current shoreline in relation to the box’s location, it’s working better now than it ever has done. “Over the past 10 to 15 years or so we’ve not needed to mechanically open the sea outlet even once”.

So while most centenarians might be entitled to taking it easy at this stage in life there’s no rest in sight for the Waihao Box – it’s more a case of 100 and not out.

ends

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