Healthy, structurally unaltered river catchments store water in the landscape naturally – both in elevated areas and on floodplains – reducing both the volume and speed of water flowing downstream.
In the UK, however, a long history of intervention by man means very few of our modern river landscapes remain in such a condition. We have lost water storage in wetlands, created hard, impermeable surfaces that accelerate runoff, and physically changed our river channels so water moves through them far more quickly than would ordinarily be the case.
In periods of heavy rainfall, this makes long stretches of many British rivers far more susceptible to flooding. This can have devastating consequences for the people that live and work beside them. Going forwards, the impact of climate change – manifested by warmer, wetter winters and more extreme rainfall events in summer – will exacerbate this problem.
Conventional (engineered) hard flood defences can reliably protect some communities, but are often very expensive and can have a hugely detrimental impact on the environment: destroying aquatic habitat and disrupting natural flood alleviation and water purification processes. Hard defences can also increase the risk of flooding downstream. As the effects of climate change on the UK’s weather systems become more pronounced, so traditional flood protection measures will become increasingly uneconomical to implement and manage, and in some cases may be rendered ineffective in protecting populated areas.
Today, Natural Flood Management (or NFM) – which works with nature to restore or recreate the natural functioning of river catchments – is increasingly viewed as a viable and often preferable alternative to hard flood defences, and a way of enhancing landscape-based resilience to climate change. Depending on the character of the landscape, this can involve creating storage ponds, planting trees, reducing soil compaction, restoring meandering rivers, and creating wetlands and leaky dams with organic materials. These measures not only mitigate flood risk, but also provide multiple other benefits (see below).
Draining an area of 520 square miles, the 50-mile River Soar is the principal waterway in Leicestershire. Much of the Soar was canalised 200 years ago, with water levels kept unnaturally high by a series of weirs and locks.
The city of Leicester has built up over centuries along the wide and flat River Soar valley, close to the head of the river’s catchment area. With the ground rising steeply to the east and west, a number of waterways flow rapidly into the Soar through heavily populated areas. This topograhic layout makes Leicester particularly vulnerable to flooding following heavy downpours or prolonged periods of rain.
Conventional flood defences have already been constructed within Leicester’s urban areas to protect homes and businesses. But with climate change increasing the frequency and severity of flooding, policy makers and practitioners are looking for new, sustainable solutions. In 2019, the Environmental Agency (EA) commissioned Ecosulis – as one of the UK’s leading Natural Flood Management practitioners – to co-design and implement a pilot project at three sites along the Soar upstream from Leicester, in Enderby, Narborough and Croft. British engineering and design consultancy Atkins was commissioned as lead designer.
As part of the NFM work, 10 trees were felled at the Narborough site to create openings in the woodland canopy. The trunks were then laid across the woodland floor in such a way that they would block the flow of flood water from the River Soar. Wood piles were also used to block up old withy beds, and a wooden bund created at the end of an old oxbow lake. This has significantly boosted the site’s water retention capacity, with peaty soil acting like a sponge, slowing the return of water to the river and groundwater during times of high rainfall.
Both the Enderby and Narborough sites are now being monitored by the EA, with both depth gauges and cameras recording water levels during high flow conditions in the River Soar (the Croft site will also be monitored once work is complete in the autumn of 2020).
The benefits of NFM extend way beyond the effective mitigation of flood risk. As such, it can be viewed as a way of sustainably managing land, rather than simply managing floods. Any assessment of potential NFM schemes vis-à-vis traditional engineered soutions should always be based on the delivery of these wider benefits, as opposed to just flood economics.
Numerous case studies indicate that the cost efficiency ratio of NFM solutions for flood management is generally higher than for their hard engineered counterparts, for the same degree of flood protection. NFM projects are typically far cheaper than major flood defence schemes, which can cost tens of millions of pounds, cause massive disruption, and which in some instances are not resilient to climate change impacts.
Moving beyond financial considerations, NFM can also provides the following environmental and societal benefits.
Creating habitats such as wetlands and wooldands boosts biodiversity and ecosystem connectivity. Many NFM measures also improve water quality, thereby enhancing habitats for aquatic species. NFM projects prompt better and more sustainable land use practice, which aligns with the objectives of the UK government’s Environmental Land Management (ELM) scheme (see following section for more details).
Reconnecting wetlands helps to manage high nutrient loads and reduces the amount of sediment suspended in the water column, thereby enhancing water quality. Improving soil structure through woodland creation or less intensive land management increases infiltration rates and reduces runoff, reducing soil erosion and also improving water quality.
Wetlands and woodlands are efficient at sequestering atmospheric carbon dioxide and then storing it. Measures that reduce surface runoff and soil erosion (such as contour cultivation) can also reduce carbon loss from soil.
Mitigating flood risk through NFM not only makes a difference to those whose lives are afftected by flooding. It also creates green spaces where people can connect with nature and improve their quality of life.
NFM measures can benefit land managers by improving soil structure, reducing loss of topsoil and increasing soil productivity.
Underpinning the UK government’s Agriculture Bill (2019-2021) – and the new Environmental Land Management (ELM) scheme that it proposes (set for roll-out by the end of 2024) – is the recognition that the UK needs more from its land than simply agricultural products, and that public payments should reward land managers for delivering public goods that cannot be delivered by the market. These “public goods” are largely environmental in nature, including things such as flood risk mitigation, carbon sequestration, wildlife and landscape beauty.
In our post-Covid-19, post-Brexit world, NFM solutions can generate added value for those involved in flood management, land managers and wider society, while simultaneously enhancing the UK’s wild nature. There is a strong expectation that the ELMs will soon support the use of private land to deliver public goods such as flood risk mitigation, and that national flood risk funds will be available for this type of approach. In the meantime, the government’s Countryside Stewardship Scheme has a range of grants for farmers and land managers who wish to adopt NFM and river restoration techniques.
Ecosulis is committed to making your nature restoration ambition a reality. To find out more about Natural Flood Management, and how Ecosulis can help you design and implement NFM solutions, please contact Nick May, Ecosulis Project Manager, [email protected] / 07966 815 226 / +44 1235 612216.
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