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What is Rewiggling, or ‘River Wiggling’?

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What is Rewiggling, or ‘River Wiggling’?

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The term ‘rewiggling’ was catapulted into the spotlight in 2022 by London Mayor Sadiq Khan, but it left many of us feeling confused. What actually is ‘rewiggling’, and why do we need to rewiggle rivers?

A Definition of Rewiggling

Rewiggling (‘re-meandering’) is adding natural-looking bends back into a river or stream if the watercourse has been straightened artificially in the past. The work may also involve enabling a river to spill out once more across sections of its ancient floodplain.

This is achieved by digging out a new course parallel to the old one that winds across the original floodplain. An alternative, lower effort technique used occasionally is removing levees and letting the river ‘rewild itself’. 

The goals are typically to reduce flooding downstream, improve water quality and boost biodiversity.

Rewilded river
The new course typically runs across the former floodplain, reclaiming its old path. This project (under construction) at Belmont Estate in Somerset was based on hydrological modelling of the most effective watercourse.

How Does Rewiggling Reduce Flooding?

In the past, landowners tried to reduce local flooding by straightening rivers, and dredging the channels so that water would flow rapidly off the land. But this was based on a misunderstanding of river systems.

While water does flow faster in straighter, deeper channels, in a wiggly river there is more storage capacity due to the bends and floodplains. 

Storms also have a much bigger impact on fast-flowing rivers, as all the water is rapidly carried away, syncing up to create a huge peak flow that creates flooding downstream. In a slow-flowing river, there is a lower peak as it takes longer for the stormwater to pass through the system.

Rewilded estuary
The bioabundance of the newly-rewilded River Otter floodplain in Devon was astonishing, with thousands of birds present in winter 2022.

How Does Rewiggling Benefit Biodiversity?

In a natural river system, there is a complex variety of slow and fast flowing water, rapids, waterfalls, bends, sandbanks, deep pools and marginal wetlands. In a straightened river, most of this diversity is lost. 

A straightened river is a ‘lotic’ system – fast-flowing water where species must cling to the bottom or swim rapidly to survive. But in a wild watercourse, there are a good mix of lotic and lentic (slow-flowing/static) systems.

Diverse systems are home to biodiverse communities of organisms, from plants to fish, microbes to birds. This means that rewiggling can create more biodiverse ecosystems, with many more niches, allowing the river system to recover a more natural level of wildlife.

This is the case even before considering the floodplain, but if the floodplain is rewilded, then the benefits are even greater. Seasonally-flooded land has huge value for wildlife (not to mention its carbon-storing capacity), and many of our most bioabundant ecosystems are floodplains (see image above).

Rewilded river in Somerset
The Belmont Estate's rewiggling project took place over the summer of 2023 - I was lucky enough to visit the site during its restoration.

Rewiggling Example: Belmont Estate 2023

Belmont is a progressive estate to the West of Bristol, wedged between the Mendip hills and the Severn Estuary on land that feels like a part of the Somerset Levels, though technically it’s too far North to qualify.

Here, what was once a healthy river has over time been straightened and dredged, but the Estate is now trying to undo this damage and restore the stretch to its former glory. They’ve appointed Ecosulis to divert the flow across a former arable field, which, over the course of summer 2023, slowly transformed into an amazing wetland complex, with a sinuous river and large ‘scrapes’.

The goals of the project are to:

  • Restore a biodiverse and productive landscape, home to abundant wildlife
  • Present opportunities for community engagement
  • Create a landscape which sequesters carbon, restores air and water quality and mitigates flood risk
 

I was lucky enough to visit the site in July 2023, and speak to Nick May from Ecosulis, who was overseeing the project. I wondered how the straightened river would be eased into its new course, and he explained that the team were created a series of raised ‘impoundments’ which would increase the level of the water in the dredged section.

One of the challenges that the team faced on site was that the former floodplain had been raised over time. Each time the river was dredged, the arisings were dumped on the bank. The result was that the channel became deeper and deeper, and the banks higher and higher. This made it increasingly challenging to connect the river to its former floodplain, which explained the use of impoundments.
 
I’m looking forward to visiting this project in the future and seeing how the site develops. As it’s in fairly close proximity to the Somerset Levels, there’s a good chance it will attract birds from that area, including Great White Egret. Perhaps there may even be a Bittern booming away from a reedbed here in the future!
Rewiggling of the River Otter in Devon
At the River Otter, large scale infrastructure work was required to mitigate the impacts of rewilding on paths, roads and an old rubbish tip.

Rewiggling Example: River Otter

Unlike Belmont Estate, the River Otter lies almost at sea level, with tidal water washing up the rewilded floodplain on a regular basis. The river here is already famous for its wild beavers, which motivated my visit in December 2022.

This is a rewilding project on a massive scale, which could be described as ‘managed realignment’. The project, while expensive at £15M, was a cost-effective way of addressing rising sea levels in an area which was protected by threatened coastal defences. 

Rather than continuing to invest in these threatened defences, which sheltered very little property of economic value, it was decided instead to relocate the property uphill and restore the estuary, benefitting from a boost in ‘blue carbon’ and biodiversity.

Here, I found a floodplain that was booming with bioabundance – by Winter 2022, much of the work has already been completed and a small river had been linked to the system upstream. This resulted in a massive area of flooded former-fields, which were covered in gigantic flocks of wildfowl.

The project, run by a broad collection of organisations, from the Environment Agency to Kier, Pebblebed Heaths and Clinton Devon Estates, had the goal of:

  • Mitigating the impacts of climate change
  • Delivering benefits for people, including new and improved access
  • Creating 55 hectares of biodiverse estuary habitat
 
The sheer scale of this project is what really stands out – at 55 hectares and £15M, it is a massive undertaking, with huge potential for creating a valuable stopover point for migrating wildfowl. These birds form part of a global, interconnected system, and our country is just one small part of this, albeit an important part. Thus, this one project has the potential to impact biodiversity and bioabundance on a global scale.
Rewiggled river Otter
The huge scale of the project is visible from this visitors' map, with the original river shown on the right and the new work shown as mudflats on the left.

Other Examples of UK Rewiggling

There are many different river wiggling projects in the UK:

Eddleston Water, Scotland – a catchment-scale experiment which is specifically designed to scientifically assess the effectiveness of different rewiggling and natural flood management interventions.

Chimney Meadows, Oxfordshire – a Wildlife Trust project designed to improve the biodiversity in a stretch of the River Thames by rewiggling part of the watercourse.

River Leith, Cumbria – a section beside the railway line which was straightened in the past will be artificially wiggled to increase capacity by 33%, to store more floodwater.

River Glaven, Norfolk – a 400m stretch of this river, which had previously been straightened and moved to the side of its floodplain, was re-engineered to meander back across it.

Goldrill Beck, Lake District – 1.8km of new channel was dug to reconnect this river with its historic floodplain and move it away from an old straightened channel.

Swindale Beck, Lake District – a new bendy path was dug out and the river rerouted into it and away from its straightened path to avoid flooding and improve biodiversity.

River Peffery, NE Scotland – a grant has been awarded to re-wiggle 800m of a straightened section, connecting it back to its floodplain and improving biodiversity.

Hyde Park, London – rewiggling streams is part of the master plan for rewilding this central London location.

Does Rewiggling Work?

From a scientific perspective, much of the existing evidence for the effectiveness of river rewiggling comes from observation, modelling and logical extrapolation (i.e. diversity in terrestrial systems supports higher biodiversity, therefore diversity in rivers should do the same). 

While there is merit in this approach, it should also be backed up by scientific research. There are some papers which indicate rewiggling has benefits, but this field of study is relatively new, so we expect to see a lot more evidence emerging in the near future.

Let’s take a quick look at some of the existing evidence:

River restoration in Poland has shown that rewiggling is likely to reduce flooding downstream, the flow is slower, and over time floodplains begin to recover their original capacity (Czech et al 2016). Biodiversity should also increase, as bendy rivers are safer places for fish and invertebrates, with slow-flowing refuges and a variety of depths (Gostner et al 2013). 

However, few studies have been carried out to verify that rewiggling works, and one recent experiment found that, while habitat variety and brown trout numbers increased, critically endangered European Eel numbers decreased (Champkin et al 2018).

Recent reviews have described how rewiggling and natural flood management case studies often lack scientific data, or their outcomes are measured in a way that restricts later analysis. A lack of data is the main problem affecting this field at the moment, but studies such as the Eddleston Water catchment initiative are designed to address this issue.

 

Rewiggled river path
Old course of Swindale Beck in the Lake District is shown in green after a rewiggling project was carried out to add in meanders. Image credit: "Swindale" by Andrew is licensed under CC BY 2.0 - Remix by Chris D'Agorne under same license.

What Complements Rewiggling?

River rewiggling tends to be carried out alongside other steps to restore the health of a river and/or prevent flooding. In fact, authorities in this area recommend a whole-system approach, rather than targeting small sections, one at a time. Several strategies can be used to complement rewiggling, including:

Reforesting upland areas: This slows land surface water runoff from storms, acting like another speed bump and flattening that peak flood height.

Leaky dams: Using trees to create in-stream blockages in smaller watercourses that also slow down the flow of water and replicate the work of Beavers.

High flow dams: These are logs which sit above a drainage channel and back up the flow of water when the watercourse is becoming full. They slow the flow, reducing the ‘peakiness’ of storm events downstream.

Restoring peatland: This creates a rough effect which slows down rain as it heads down hillsides towards watercourses. Some sources claim that they act as a ‘sponge’, but this is disputed. There is evidence to show that they reduce the ‘peakiness’ of downstream water flows.

Where Did the Word 'Rewiggling' Come From?

‘Rewiggling’ isn’t a scientific term – the correct word is ‘re-meandering’, but the principles behind both are the same, and the science is sound. It has been claimed that the term ‘rewiggling’ or ‘re-wiggling’ is a parody of ‘rewilding’

Whatever the origins, rewiggling is basically undoing channelisation – helping rivers to break free of their artificial path by creating new meanders or removing levees, and connecting the river back to its natural floodplain. Rewiggled rivers are not just wigglier – they’re also wider, shallower, more varied in depth and slower (Czech et al 2016).

 

Champkin, J. D., et al. “Responses of fishes and lampreys to the re‐creation of meanders in a small English chalk stream.” River Research and Applications 34.1 (2018): 34-43.

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Czech, Wiktoria, et al. “Modelling the flooding capacity of a Polish Carpathian river: a comparison of constrained and free channel conditions.” Geomorphology 272 (2016): 32-42.

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Gostner, Walter, et al. “The hydro-morphological index of diversity: a tool for describing habitat heterogeneity in river engineering projects.” Hydrobiologia 712.1 (2013): 43-60.

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Hankin, Barry, et al. “Integration of hillslope hydrology and 2D hydraulic modelling for natural flood management.” Hydrology Research 50.6 (2019): 1535-1548.

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Sayers, P. B., et al. “Climate Change Risk Assessment 2017: Projections of future flood risk in the UK.” Research undertaken by Sayers and Partners on behalf of the Committee on Climate Change. Published by Committee on Climate Change, London (2015).

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Rippon, Stephen. Landscape, Community and Colonisation: the North Somerset Levels during the 1st to 2nd millennia AD. Council for British Archaeology, York, 2006.

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