The Ecologist

A pair of beaver dams in Bamff, Perthshire. Photo: Paul Ramsay.
A pair of beaver dams in Bamff, Perthshire. Photo: Paul Ramsay.
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Carlisle floods: bring back the trees, and the beavers!

Oliver Tickell

7th December 2015

The key to reducing the risk of more floods like those in Carlisle is to realise that conventional 'flood defence' can never provide security against the ever more extreme weather events that global warming will bring. We must embrace natural solutions to holding back flood waters: more trees; and bring back the beavers!

It's time for governments to move beyond the usual rhetoric of 'flood defence' and to move into a new era of rebuilding natural resilience to extreme climate events, using the gifts that nature herself has given us.

Northwest England has been struck by truly apocalyptyic flooding after Storm Desmond hit this weekend.

With some 5,000 people flooded out of their homes in Carlisle, another 9,000 premises still at risk of flooding, and damage likely to be in the hundreds of millions of pounds, it has become a political hot potato.

The £38 billion of flood defences recently installed by the Environment Agency failed to stop the floods - causing acute embarassment for Prime Minister David Cameron, who is visiting the area today.

So what's it all about - and why weren't the flood defences up to the job? Actually, it's surprisingly simple. A lot of rain fell. More rain than has ever fallen anywhere in the UK before in a 24-hour period.

According to the Met Office, 341.4mm of rain (about 14 inches) was measured over 24 hours in the Lake Distract at Honister Pass in Cumbria, beating the previous UK record set at Seathwaite, Cumbria, of 316.4mm on 19th November 2009.

And with global warming, we can expect more such 'extreme weather' incidents, and more serious ones too. The only thing is, we don't know where they will hit, or when. Last winter was fairly dry. The winter before, it was the south-west of England that copped it.

But what we are learning is that traditional flood defences, which aim to constrain floodwaters into river channels, are only ever part of the solution, at best. Because by the time the surge of water is in the river channel, it's already too late. The Government has committed to £2.3 billion worth of flood defences over six years, but if that's all it does it will be (excuse the pun) money down the drain.

The real action is in the headwaters

How come? Because current flood protection as practised by the Environment Agency is all about moving water downstream as fast as possible. In the case of Carlisle, which is near the sea, that's not altogether daft. But it's definitely not enough. We also have to look to where the water is coming from.

Carlisle is a lowland city with three huge upland areas standing right behind it: the Lake District National Park, the Northumberland National Park, and the North Pennines AONB, with rivers that drain them converging on the city and its surrounding flood plain.

Dump a flood of water onto all these hills and what's it going to do? In the state they're in it's going to run off, fast. That's because those uplands have been largely denuded of tree cover and subjected to deliberate drainage schemes on the high moors intended to make them more productive for sheep rearing.

Moorland drainage is, thank heavens, no longer official government policy. But the drainage ditches and trenches are still there. In many cases they have been eroded into huge gullies, cutting five metres or more deep into the landscape down steep-sided hills.

Other lower lying hillside lands have likewise been drained for agriculture, if not by government officials and agencies, by farmers trying to squeeze more production out of their fields. The result is that as you move down into the river channels, they are severely eroded, their banks usually treeless from overgrazing, and ready to turn into surging torrents the moment a storm hits.

So the answer is, again, not rocket science. The storm waters must be held back into the moors, bogs, fields and headwaters, so that they don't just made a headlong dash for Carlisle and the sea, but are given the chance to replenish soils and aquifers, and are released only slowly into the main streams and rivers.

We need more trees

It's no secret that just having trees in the landscape helps rainwater to infiltrate into soils. The rationale for this - and the evidence to back it up - was presented in an article on The Ecologist by Mike Townsend (then Principal Advisor to the Woodland Trust) in March 2014. In it he showed that:

  • hedgerows and shelter belts reduce surface water runoff from fields which carries with it nutrients and soil;
  • planting tree belts across upland sheep pasture led to a 60-fold increase in water infiltration compared to other locations without tree belts, due to the improved soil structure and the effects of tree roots;
  • when this effect was modelled across the catchment the result was a potential reduction in peak stream flows of as much as 40%. "This is clear evidence that integrating trees into our upland farms will play a part in reducing flood risk downstream", he wrote.

Trees also bring benefits in lowland floodplains. According to Forest Research, woodland strategically located on floodplains can mitigate large flood events by absorbing and delaying the release of flood flows.

Research based on the River Cary in south-west England suggested that a 2.2km reach of floodplain woodland could increase flood storage by as much as 71%, delaying the flood peak progressing downstream. "This suggests there are opportunities for creating strategically placed floodplain woodland to alleviate downstream flooding," he wrote, "particularly the increased risk associated with climate change."

Townsend also wrote of Cumbria, and its 112,000 ha of common land, much of which is overgrazed and deforested. Working with landowners and graziers, the Woodland Trust has been planting 65,000 trees and shrubs on 110ha (270 acres) of Tebay Common.

That's good work - but the area is small compared to the size of the problem, which extends across much of the UK and its uplands in particular. A major national tree planting effort is called for to build our national resilience to future flood events.

Next, beavers, our native landscape engineers

Trees are important for another reason too. They are food for beavers, and beavers use them to build their dams. And beavers will do all the work of damming up the streams and gullies for us, free of charge. And that's absolutely key to restoring landcapes and making them water retentive.

We should therefore select water-loving species that are palatable to beavers - like poplars, willows, sallows and alders - and establish them along watercourses, ditches, streams, ponds and eroded upland gullies.

Northumberland National Park is currently trying to block its eroded gullies by hand to avoid causing further damage by machinery, and it's hard, expensive work. Helped by volunteer labour, the Park is laying 146 'coir logs' or 'sausages' into gullies and eroded peatlands in order to hold waters back and improve downstream water quality.

"The team are confident that the new technique will make a real impact on the 1.5km of eroded gullies near Carter Fell on Whitelee Moor", the Park reports. "The aim of the work is to 'slow the flow' of water and stop peat sediment from entering the River Rede. The Rede is known for its freshwater pearl mussels, which need extremely clean water and gravel beds ...

"It is hoped that the coir logs will last about 5-10 years before they naturally break down. This will allow time for the bare peat gully walls to become re-vegetated and slow the flow of water."

They must be praised for their efforts, but there's no doubt that beavers would make an even better job of it, and at much lower cost, so long as we provide them with the trees they need to eat and build their dams with, and give them the freedom to reproduce and spread across the uplands and valleys to recreate truly living landscapes.

The dams would not just reduce flood risk: they would also prevent the summer droughts to which the area is also prone as a result of the rapid water drainage, and restore healthy river flows throughout the year.

Government must move beyond the old rhetoric of 'flood defence'

The irony here is that - as noted in an article on The Ecologist this weekend - beavers are actually being shot in Scotland with the tacit approval of the Scottish Government and its wildlife agency Scottish Natural Heritage, in a clear caving in to the country's powerful landowning interest.

So please Scotland, if you are have too many beavers, send them south to Cumbria! But the truth is that Scotland needs its beavers every bit as much as England does - and for exactly the same reasons.

I would not wish to pretend that every flooding event can be prevented by planting trees and restoring beavers. There will still be a role for orthodox 'hard engineering' in protecting vulnerable flood plain settlements. But that approach alone can never provide the protection we need, especially with the rising power and ferocity of the weather we must expect in a warming world.

It's time for governments to move beyond the usual rhetoric of 'flood defence' and to move into a new era of rebuilding natural resilience to extreme climate events, using the gifts that nature herself has given us.



Petition: 'To stop UK floods: plant trees, and stop shooting beavers!'

Petition: 'Make planting trees a priority to reduce flooding by improving soil and drainage' (official petition to UK Government).

Oliver Tickell edits The Ecologist.


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