Wetlands, flooding, and floodplains. Arguably the most abused landscape in Britain?
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By Professor Neil Entwistle, Professor of River Science and Climate Resilience
Wetlands are found across the world, ranging from giant deltas, mighty estuaries and mudflats, to floodplains and peat bogs. Humans and wildlife have relied on them for thousands of years, yet over centuries many have been altered by humans and exploited. For example, between 1970 and 2015, 35% of wetlands were lost to changing land and water use with more than 25% of all wetland plants and animals at risk of extinction.
Our research revealed the near complete destruction of wetland habitats on floodplains across England. On the 555 UK floodplains we studied, 85% of rivers had no wetland associated with them at all. Historic embankments and dredging conveyed water downstream and disconnected rivers from their floodplains. Historic government funding realigned rivers and installed underground drainage pipes to propagate water off the landscape to quickly transfer rainfall into rivers and drains, preventing the natural waterlogging of floodplain soils. Over several decades, river tributaries were rerouted to flow along valley edges, drying out wetland areas even further. This was primarily done to reduce the perceived flood risk in towns and cities for agricultural and land use purposes.
Floodplains are the generally flat and low-lying lands which form around rivers as they deposit sediment. Modern understanding now recognises fluvial systems as diverse and dynamic environments with associated freshwater ecosystems providing suitable habitats for many plant and animal species. Naturally functioning river/floodplain systems can help us become more climate resilient; promote ecological diversity and holistically reduce flood risk within a river catchment. For example, in January significant rain across Cumbria saw the restored re-wiggled river at RSPB Haweswater inundate the floodplain and slow flood flows toward Carlisle.
Heavy rains in Worcestershire saw the River Teme occupy its floodplain all the way from Bransford to its confluence with the Severn.
The permanent or seasonal inundation of floodplains with flood water gives rise to mosaics of wetland habitats which are home to a variety of plants and animals that have, over time, adapted to these wet conditions. Allowing these habitats to regenerate could lock up carbon that would otherwise warm the atmosphere and fuel more extreme weather. That’s because the often-overlooked resource of wetlands is that they hold huge amounts of carbon - more than that of rainforests! The reason they do is because the damp and low-oxygen conditions of wetlands make them very good at slowing the rate at which organic matter decomposes. This ensures the carbon contained in all the plants and animals that die in wetlands stays out of the atmosphere for a long time. Peatlands for example, cover only 3% of Earth’s land surface but store 30% of all land-based carbon.
Across the country, pioneering work in river restoration has been shown to substantially mitigate the impact of historic alteration to our rivers. For example the Cumbrian River Restoration Strategy recently won the European River Prize for the ambitious programme to restore and improve rivers in the Lake District improving almost 100km of river length and restored over 150 hectares of floodplain across the catchments of the Rivers Eden, Derwent and Kent. It has also reduced flood risk, removed plastic from rivers and boosted biodiversity in the region.
During last year’s drought, many of these areas of restored wetlands remained wet during the highest temperatures recorded in the UK. This is important as our climate continues to warm as lakes, peatlands, and many wetlands in farmlands are precious natural assets in our landscapes; they are the hydrological buffers that limit floods by slowing the flow of water downstream, they manage nutrients in our soil, they replenish underground water reserves we use for drinking and they sustain freshwater biodiversity.
We should continue to champion restoration of floodplain wetlands, and provide incentives for landowners to resume natural function of our rivers, floodplains and catchment landscapes. There are exemplar projects dotted across the country, for example the National Trusts ‘Riverlands’, the work that River and Wildlife Trusts do. There is also thriving farming community who have linked with all sorts of other organisations to provide space for water and receive payments for doing so. 40% of the world’s species make their home in wetlands, but unfortunately, these habitats are also among the most threatened.
Restoration projects vary in size but using current research and understanding we can rejuvenate natural process and un-engineer river channels, we can break underground drains which can immediately transfer permanently flowing water onto the floodplain. The below example (from the work done by Eden Rivers Trust and Lowther Estate, funded with the Environment Agency) resumed an old flow route and restarted the process of storing water and sediment on land, rather than moving it rapidly downstream. The result is a patchwork of open water within a wider, boggy landscape, which acts like a sponge for greenhouse gases that can hold and dissipate flood waters. This area is now thriving with wildlife and ramblers.
These interventions are already bringing back wetlands across UK floodplains in pioneering work. This work complements the national drive to reforest and restore ecosystems to absorb CO₂ and a study suggested that restoring just 15% of the world’s lost wetlands could lock up 30% of the total increase in atmospheric CO₂ since the Industrial Revolution, while preventing 60% of expected species extinctions.
We can make a difference; we are making a difference, but we need to ensure that the message is conveyed in the right way. Dredging rivers is often seen as the answer to flooding. Yet it is more often not the answer. Our research shows that natural sediment management through a well-connected river and floodplain environment, displaying a naturally complex mosaic of permanent and temporary aquatic habitats helps to mitigate flood risk.
In addition, our personal connection with nature, and particularly wetlands, is essential for maintaining our physical health and wellbeing. Walking in nature, visiting wetlands and observing their wildlife can help us regain a sense of peace and provide us with a place to recuperate and escape life’s daily stresses.
Find out more about Neil’s work at https://www.salford.ac.uk/science-engineering-and-environment
https://www.salford.ac.uk/our-staff/neil-entwistle or follow him on twitter at @Salfordhydro
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