Wednesday, 23 March 2016

Using natural flood management to protect communities against the effects of storms

Dealing with flooding needs intelligent thinking - and working with nature:
Futures Forum: Making Coastal Communities Resilient >>> Green and Gray >>> Understanding the Shades of Resilient Infrastructure
Futures Forum: Flooding: government inquiry into a joined up approach >>> slowing flood water, redirecting farming subsidies, living with nature and rewilding ... and planting a few trees

Clinton Devon Estates have been working on a project to give the River Otter a little more room to move:
Futures Forum: Climate Week in Sidmouth >>> Clinton Devon Estates @ The Climate Variety Show >>> Friday 11th March

This blog has considered ideas from the Engineering and Technology Magazine:
Futures Forum: Flood management: how to hold back the waters >>> >>> "It will require flood schemes to be developed with communities and not just for them."

Here is another piece from the same source looking at 'natural flood management' methods to reduce flood risk:

What more can we do to protect communities against the effects of storms?

By Rebecca Pool
As communities across Cumbria, Lancashire and Yorkshire in the north of England come to terms with flood damage from Storms Desmond, Eva and Frank, the pressing question on many minds is how could this happen again?
In 2005, heavy rainfall in the Lake District and the Pennines led to floods across Cumbria. Then in 2007, widespread deluges brought the same again from Yorkshire down to South Wales. Come 2009, huge volumes of rain overwhelmed land and rivers across Cumbria, and downpour after downpour in 2012 delivered widespread flooding across the UK.
Before the latest spate of devastating floods, the government had stepped in to bolster flood defences in high-risk, storm-ravaged Cumbrian communities.
A £38m flood defence scheme in Carlisle included raised defences, pumping stations and flood gates. Cockermouth is home to the UK’s first self-closing barrier: a £4.4m floating wall lining 115 metres of riverbank and designed to rise by one metre, come flooding. And down the road in Keswick, £6m flood walls, embankments and flood gates were built to protect against the worst.
Yet in December 2015, despite these efforts, exceptional rainfall on already saturated land saw flood defences ‘overtopped’ in all these towns and more, and residents could only watch in horror as the floodwaters returned.
“When designing systems you have to calculate what flood return period you are going to work to and what probability of floods you are going to hold back,” says Bob Sargent, UK-based hydrologist consultant and president of the British Hydrological Society.
“There’s always the possibility of a bigger flood and that’s exactly what happened here,” he adds. “From an engineering point of view, the defences didn’t fail, they performed exactly as planned.”
Indeed, defences at Keswick, Cockermouth and Carlisle were all designed to at least protect against a 1-in-100-year flood but clearly this wasn’t enough and as Sargent points out, the nation is experiencing “quite a few” higher-risk flood events now.
“Overtopping is a fundamental problem when trying to defend communities, such as Carlisle, that are at the bottom of a [water] catchment area,” he says. “We can’t just build defences higher and higher – flood defences for a 1000-year event would be too expensive to build everywhere and impractical in many cases. “The real issue now is what else can we do?”
For those living in flood-prone regions, a range of actions are advised to increase the ‘resilience’ of a building. Raising electrical circuitry up walls, using lime plaster instead of gypsum plaster, avoiding chipboard for kitchen furniture are just a few measures.
But like many in his field, Sargent is a firm advocate of what’s called natural flood management to reduce flood risk. Put simply, this is returning the river catchment closer to its original state in a bid to hold water back, preferably in the soil.
As the hydrologist highlights, today’s agricultural methods typically see soil compacted with heavy machinery, crops destroying soil structures and land left bare over winter months.
“There’s a whole range of activities that effectively increase the surface run-off of water and increase peak flows,” he says. “But we need to manage our water better so it flows less rapidly [into the catchment], and we reduce peak flows.”
For example, Sargent suggests growing so-called shelter-belts in fields. “You only need a narrow strip of woodland across a slope to open up the soil. Tree roots get right down into the soil and allow water to percolate there, cutting off the water flows going downstream,” he says.
Likewise, hedgerows, embankments and small reservoirs in fields would also retain water, reducing peak flows further. Clearly, such measures aren’t rocket science; nor are they new.
Following the devastating floods of 2007, the UK government commissioned the ambitious Pitt Review to ensure flooding at this scale didn’t happen again.
Eight years on and many floods later, has it worked?
Sargent has his doubts. As he points out, a lot of the review focused on managing upstream water catchments to reduce peak flows, but in his words: “We’re still having the same arguments with farmers that want to drain their fields.
“Generally after floods we get a strong reaction, then it subsides and everyone forgets until the next time.”
Still, he is certain that natural flood management will help. “We can’t destroy agricultural areas to protect towns that perhaps shouldn’t have been built [in a flood plain], but working together would be a good idea,” he says.
“Frankly, I think some regions will have to be abandoned if [floods] carry on at this rate, but by reducing peak flow, we can also adapt.”

Flood defences: What can we do to hold back the waters? - E & T Magazine

See also:
Futures Forum: Flooding: "stop building houses on flood plains" ... ... ... "and find a balance between the needs of our wildlife, the threat of an increasingly wet climate and the requirement of food production."

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