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Waste disposal . . . The Victoria Flats landfill sits beside the Kawarau River. Central Otago resident Nick Loughnan says the facility generates "plenty of stench", as well as large amounts of toxic leachate. PHOTO: STEPHEN JAQUIERY

Galloway resident Nick Loughnan poses questions about Central Otago rivers and landfill in this week’s Protecting Our Water column.

Waste disposal . . . The Victoria Flats landfill sits beside the Kawarau River. Central Otago resident Nick Loughnan says the facility generates “plenty of stench”, as well as large amounts of toxic leachate. PHOTO: STEPHEN JAQUIERY

Thankfully, after multimillion-dollar wastewater upgrades in Wanaka, Queenstown and Cromwell, we are hugely better off than we were 10 years ago with regard to the combined treatment and quality of wastewater discharges into our river systems. They weren’t a good look.

But there are other issues around the Kawarau River that need to be faced up to.

We have our 20-year-old regional landfill on an elevated terrace beside the Victoria Flats bridge near Gibbston, with a capacity for three million tonnes of waste. At present around 35,000 tonnes are dumped there each year.

The projected life of this facility is perhaps another 40 years, and consents for it are due for renewal in 2032. A weekly load of 75 tonnes of sewage sludge which had been dumped there until 2016 is now trucked off to Winton.

But the Victoria Flats landfill still generates plenty of stench for local Gibbston residents, along with large amounts of toxic leachate. Where does this liquid end up? And with the landfill’s boundary less than 100m from the Kawarau River, how secure is this colossal cesspit?

Were seismic risks factored into its location and design? The recent Fox River landfill breach warns us of the danger of siting dumps so close to major rivers.

Then there is the wildly beautiful Shotover River – a steep and constantly eroding catchment feeding the Kawarau River with sedimentary gravels. These once flowed out to sea, but our two hydro dams and the lakes behind them have become giant sediment traps.

The build-up in the Clutha had filled Lake Roxburgh with an estimated 54million cubic metres of sediment, halving its storage capacity and contributing to the damage from three major floods in the 1990s, which partly inundated Alexandra.

This sediment problem has now migrated upriver, since Lake Dunstan was formed behind the Clyde Dam; 1.4million cubic metres of Shotover sediments annually settle in the area below Old Cromwell up to the end of the Kawarau Gorge – roughly equivalent to the amount of concrete poured for the Clyde Dam. Multiply that load by 26 (years since the dam was commissioned).

A flood of the magnitude we experienced in 1999 would now redefine the shoreline around Bannockburn. And Land and Information New Zealand has just surrendered to the growing sediment problem at the Cromwell boat ramp.

Does the buck now stop with Contact Energy?

One hope we have for reducing this serious problem is by planting trees on the Shotover’s erosion-prone slopes. They work.

Perhaps we need to rethink the eradication plan for wilding pines in this catchment. Or if we are going to be fussy about the variety, then grab some of those one billion other trees now on offer. They all grow beautifully up there.