charles rangeley-wilson – writing about fishing, travel, rivers, conservation

The Impact of Dredging


“We can’t go round it,” said the river. “We can’t go over it. Oh no! We have to go through it!”

A few months ago I mentioned that Owen Patterson (Secretary of State for Environment, Food and Rural Affairs) was planning a relaxation of the by-laws governing dredging in small rivers. We were not long out of the wettest twelve months anyone could remember and the farming lobby must have placed the minister under some pressure to do something about all the fields that were under water.

Dredging a river might appear an obvious way to get it to hold more water – logic based on the idea of the bigger the bucket.

Poor logic when it comes to rivers.

Rivers are not static storage devices, like buckets. Rivers are dynamic and water flows through them. How much is governed by rainfall and how fast by gravity. Water put at the top of a hill wants to go down it, simple as that. If a lot of water is put at the top of a hill, the storage capacity of the river is soon irrelevant, because the volume of water the river can process is limited by the most restricted points the water has to flow past, no matter how wide or deep the river is made between these restrictions.

So far, so obvious. But in fact our landscape has been managed for fifty years according to the very opposite logic. The pinch-points on this nation’s rivers are, ironically, all man-made: bridges, weirs and towns. But with impeccable daftness, and in the name of flood prevention, we have ruined the natural rivers between these obstructions and left the obstructions alone. So for fifty years we’ve tried a logic that doesn’t achieve what it sets out to, if anything makes the situation worse, the by-product of which is an immensely impoverished landscape.

Timely then that the Environment Agency has just published (complied by Judy England and Lydia Burgess-Gamble) a paper called Evidence: Impacts of Dredging, a summary of all current sources of information relating to dredging and its effect on flood prevention, river management and the ecology of our rivers. I’m hoping Owen Patterson has a copy because the paper concludes:

• Dredging does not translate into a lower risk of flooding.

• Impounding structures have a much greater and over-riding impact on water levels.

• Dredging can cause flooding or make it worse.

• Channels that have been dredged fill with silt.

• Dredging damages ecology.

• If left alone rivers become self-managing and self-cleansing.

The only sustainable, long-term way to manage flooding is to do exactly that – manage flooding. We should be thinking about how to slow the flow of water by catching it in the landscape: by restoring wetlands, not scouring them. There’s no reason why this can’t go hand in hand with profitable farming. But it does need to happen at a scale which proves that it works. 

Right now we are stuck in an ebb and flow of muddled thinking and inadequately-funded initiatives, and we are prey every time it rains hard to revisionist logic and the sound of a thousand diesel motors preparing once again to do battle with the elements.

2 Responses to “The Impact of Dredging”

  1. Mark Prina

    Thank you for pointing out the folly that our dear Oxford economics and politics graduates are about commit. They, of course, know absolutely nothing beyond their narrow sphere of training but, unfortunately, have wormed themselves into running the country. Oh for some politicians with vision, wisdom and honesty.

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