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As a freshwater ecologist, I see flooding as a natural process. While flood schemes are essential for protecting people and property, the minute you start to control floods you start changing how rivers work. Things like how they naturally support plants and animals, and even people. It’s a global problem.

Our flood schemes were put in 50-60 years ago to build a strong economy and communities, and they still do that. However, expectations have changed. There’s now a much greater appreciation of the ecological values of rivers, and an expectation that the management of our rivers be sustainable. It’s our council’s job to respond to changing community expectations while still living up to our responsibility of protecting people and property from flooding. It’s a challenge, but the possibilities are exciting for our ecologists and engineers.

One of the issues with flood schemes is they tend to block the movement of plants, animals, energy and sediment, both in an upstream-downstream direction but also sideways, between rivers and floodplains. One thing we’re doing is looking at replacing our older flood pumps and floodgates with more environmentally friendly models as they come up for renewal.

Maintenance can also have an environmental impact. If you’re working in channels with excavators then habitats can be damaged or removed. Over the last few years, we have been improving our best practice for stream work. We do things like relocate fish so they don’t get stranded on banks or trapped in channels that have been cut off from the main river.  Another thing we are starting to do now is reinstall wood back into rivers, or leave it in place, where before it was treated like a blockage or problem. If done right, this helps provide fish habitat and helps the river function better, stops erosion and reduces flooding downstream. We tie them down with cables or bury them into the banks so they are anchored in place and can’t move.

In the Lower Piako scheme, we’re trialling planting to improve the habitat that river margins can provide because at the moment they’re dominated by weeds and disturbed by maintenance. It’s a really challenging environment as it’s tidal and there’s heaps of sediment moving around. Our catchment management teams already do a great job working with landowners to fence and plant riparian areas prone to erosion to improve water quality but planting also plays a massive role in managing floods.

For me, all this work is exciting: working with natural processes rather than against them. We’re protecting communities, improving ecosystems and saving money. It’s win-win, really.

fish recovery

Mike Lake catches fish for relocation during maintenance works.

 

"For me, all this work is exciting: working with natural processes rather than against them. We’re protecting communities, improving ecosystems and saving money. It’s win-win, really."

 

Oamaru Stream

Wood installed in streams provides fish habitat and helps prevent erosion.