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Living in an evolving landscape

Living in an evolving landscape
David Clark

We have all seen images of the impact of Cyclone Gabrielle along the East Coast of the North Island, the damage from which will be life changing for many people. We saw this in our own District two years ago.

Recently there has been much made of reports and discussion by our own Regional Council on flood management and conjecture raised around how closely we interact with the river margins.

Historically humans lived nomadically and simply moved when the landscape changed. In more recent times, we have sought to develop communities and assets that we view as more permanent, so that brings us into conflict with the natural processes.

In Canterbury, if you dig a hole 50m deep, you will find a stone, very similar to one from the current surface, and a close match to one in what we regard as the riverbed. On the Heretaunga Plains and in the Esk Valley, digging a hole of any depth will find you layers of silt deposited by a succession of flood events over time.

With regard to the current location of rivers, the Ashburton River is where it is, obviously. It is not running down north of Racecourse Road and out to sea via that big gully at Wakanui. The Waimakariri equally is in what we regard as it’s correct place, however if we had popped up at a different point in time, it would have been running down the Avon or out through Lake Ellesmere.

I would suggest it is particularly arrogant to think the migration of rivers in Canterbury or the erosion of the Alps depositing shingle out onto the Plains has magically stopped now that we humans have arrived and decided to build communities. Equally, I don’t think the current layer of silt that the good folk of Hawkes Bay currently reside on is the final and last layer of silt to be deposited on the Heretaunga Plains.

Nor do I think it is appropriate to give ourselves an excuse of disassociation from these ongoing natural processes by blaming Climate Change.

What we need to do is learn how we interact with this changing landscape and how we accept that the processes that formed the Plains are ongoing.

I get very frustrated when various groups choose to point the borax at farmers as has been done lately on the margins of rivers. It would seem they are opposed to any agricultural development on a very broad definition of a Flood Plain or historic River bed.

So, if that development is inappropriate and the river should be let go free to find it’s own course, what are we going to do with the EA Networks Centre in Ashburton? Because it is clearly obvious to all that the high terrace between the town and the pool was carved by the river.

Equally, a quick look at an aerial photograph of the land surface west of Christchurch Airport clearly shows swales of a very recent riverbed. So, if we are going to let any river “run free”, shall we start with the Waimakariri, held in by three layers of stopbanking? Arguably regular, natural flushing of Lake Ellesmere by the Waimakariri would sort out any concerns about lake water quality.

We need to start and have honest, realistic discussions about how we live on this evolving plain, how we address the ongoing migration of shingle from the Alps out onto the Plains and how we fund the work that is required.

by David Clark.