Flooding in the Somerset Levels and the dredging debate

The winter of 2013/14 saw the UK battered by the St Jude's Storm of early December and persistent heavy rainfall and storms which lasted into early February, likely to be linked to abnormal patterns in the North Atlantic Jet Stream.

Submerged Somerset Levels, January 2014

      As well as intense coastal erosion in parts of Devon, Dorset and Cornwall, the Somerset Levels was submerged for weeks, with unprecedented flooding threatening homes, businesses and farmers' livelihoods.The flooding sparked nationwide debate as who should take responsibility for the floods and their impacts, and of the future of flood management of the area and the rest of the UK.

 The Somerset Levels, which is the home to 170,000 acres of high quality farmland, is a natural floodplain which is served by four main rivers: the Parrett, Tone, Brue and Axe. Flooding is not in any way new to the region, however this years flooding has caused serious and potentially long-lasting impacts:

- 600 homes were affected in the area, causing loss of possessions, psychological effects, and long term consequences of potentially tripling insurance costs and plummeting house prices.

- Villages were completely cut-off and major road links were blocked, causing transport delays, disruptions to emergency services and local businesses.

- Farmers were amongst the hardest hit, with 17,000 acres submerged, many farmers had to sell or slaughter cattle. The economic cost of the floods to the region's agriculture industry is likely to be £10 million.

Local residents call for the Environment Agency to dredge

Many argue that dredging is the Somerset Level's answer to reduce the impacts of future flooding in the area and local residents and MP's have crcriticizedhe Environment Agency for not dredging the rivers in the area efficiently, and blames this as the cause of the flooding.

What is dredging?

Dredging involves removing silt and other built up materials from the river channel to increase it's capacity and therefore limit fluvial flood risk. Experts suggest that managing rivers can increase the river channel's ability to hold higher levels of water flow following extreme weather. Farmers and residents of the somerset levels have expressed concern that their rivers have not been dredged enough, with one farmer explaining to the BBC that the rivers were '42% silted up'.

Are there arguments against dredging?

Despite dredging, or de-silting, having the potential to alleviate flood risks in many parts of the UK, some experts and environmental groups protest that dredging does not provide an environmentally or economically sustainable solution to flooding.

- Expense: dredging and river management often involves very specialist and costly eqequipment which can limit the environment agency or a local council flood defence budget. Dredging is also not a long-term fix as silt build up is continuous and therefore dredging needs to be carried out frequently. Therefore, in the somerset levels the cost of dredging would need to be weighed against the value of the land protected.

- Increased downstream flood risk: removing river silt can increase its flow velocity and  therefore can increase the risk of flooding downstream from the dredged site.

- Increased erosion: dredging can also increase the erosive power of the flow due to reduced friction from sediment, which in high energy river systems particularly can cause banks to erode, potentially increasing the risk of flooding.

- Wildlife and ecological impacts: wildlife and environment groups such as the RSPB warn that dredging can lead to unexpected negative knock-on effects to river ecosystems Scientists suggest that removing vegetation from river channels reduces shade and therefore increases temperatures. This can lower the oxygen levels in the water, impacting river species and the whole ecological cycle.Surveys also suggest dredging impacts birds, with some areas where dredging as been used experiences falls in the number of some wading bird species. The somerset levels has several SSSIs (sites of specific scientific interest) and is home to a vast variety of rare species, therefore the  ecological impacts of dredging would need to be considered carefully.

Are there effective alternatives to dredging?

Managing land-use on flood plains, such as reducing intensive use and introducing floodplain woodlands or wetlands, can encourage natural infiltration and prevent widespread flooding. These management techniques can be described as working with nature to protect valuable landscapes, rather than working against it, as dredging has been accused of doing. It is important that these management methods are used alongside dredging where it used to maintain a holistic approach to flood management that minimizes unwanted effects to the environment.

What are the current plans for the Somerset Levels' future?
The environment agency have released a full briefing into their action plan for flood control in the somerset levels, an executive summary can be found here.
With the risk of flooding in the somerset levels is almost certain to increase with factors such as climate change, rising sea levels and urbanisation increasing surface run-off, there is mounting pressure from local business, residents and farmers in the region to protect their land and resources. However, whatever response methods used to protect the region, a compromise must be made to protect the ecology and ensure other areas do not suffer increased flood risk as a result of dredging.

Further reading:
- A report by CIWEM about the risks and merits of dredging:                         http://www.wcl.org.uk/docs/Floods_and_Dredging_a_reality_check.pdf
- This BBC article, and others in the 'related articles' section give balanced perspectives on   the flooding and dredging: http://www.bbc.co.uk/news/uk-25911391