How nature can help prevent flooding

In England alone, more than 5 million properties – one in six – are at risk of flooding.

The approaches we have relied on in the past are no longer enough to protect us from the risk of floods that we may experience today and into the future. Now flood risk managers are increasingly drawing upon a greater range of approaches to make us more resilient to flooding.

Wildlife Trusts are leading the way in delivering ‘Natural Flood Management’ Solutions that slow the flow of water through catchments, reducing flood risk downstream. These work alongside other flood risk management techniques to give communities the best options for dealing with flood risk.
 

Traditional flood defences 

Traditional flood defences like flood walls and embankments confine water to river channels, preventing it spilling out in particularly vulnerable areas like towns and cities. In rural areas there can be opportunities to set these embankments back, allowing water to flow out into the floodplain. This creates extra capacity to hold water and prevents it rushing to built-up areas downstream. As a new Environmental Land Management (ELM) Scheme is developed in England based around the concept of ‘public money for public good’, The Wildlife Trusts hope to see farmers and land managers supported to store flood flows on their land, protecting communities downstream from flooding.

Nature flood management solutions

Techniques that work with natural processes are increasingly recognised as important in helping us to manage the risk of flooding. Our landscape today has been modified to make it less and less permeable through hard paving of urban areas, the conversion of natural habitat to other land uses, and the compaction of intensively-managed agricultural soils. This means that our landscape is less able to capture water by holding it in soils and vegetation, or allowing it to percolate through into permeable rocks below. Instead, water flows overland, quickly collecting in rivers and then overwhelming flood defences that can no longer cope.

It is too costly – both financially and environmentally - to construct ever-higher defences, but there are a plethora of techniques that can help us hold water back in the landscape and lessen the need for those defences. Wildlife Trusts are using a range of these Natural Flood Management measures to slow the flow of water through catchments, including creating and restoring ponds and wetlands, enhancing soils so that they can hold more water, planting trees to slow overland flows and aid infiltration, and constructing woody features, like leaky dams, in channels and floodplains to hold back water.
 

Putting these solutions into practice

A range of habitats or habitat features help to hold water in the landscape, including:

• Woods, trees, hedgerows: tree cover intercepts rainfall, so it hits the ground with less force and doesn’t run off so readily. Trees take up water for growth, allowing some to evaporate back to the atmosphere, but more importantly their root systems help water to penetrate into the soil, again reducing runoff.
• Ponds, scrapes and wetlands: Wetlands and hollows in the landscape collect water, holding it during wet periods, and releasing it slowly during dry periods.
• Peat bogs; Sphagnum moss can hold 20x its weight in water!
• Wet grasslands: Rough, tussocky grasslands like the Culm grasslands in Devon are extremely effective at storing water. Research has shown that 11 times more water leaves intensively managed grasslands than Culm grasslands during storms, increasing the risk of flooding downstream. Bare soils will allow even more runoff.