Tackling flooding in urban areas

Centenary Park in Rotherham forms part of the town's flood alleviation scheme

Flooding in urban areas is caused by many pressures on the natural environment from problems upstream as well as the fabric of the town itself.

These include the degradation of upstream habitats which store water, the building of houses and businesses in the natural floodplains of rivers, an increase in impermeable surfaces across towns and cities and drainage systems that cannot cope with the huge volumes of water that run off them in high rainfall events.

There are now many good examples of how the creation of flood storage areas upstream of settlements can function successfully to protect people and their homes and businesses.  Very often these areas also bring benefits for wildlife and people throughout the year.  But there is an urgent need to create more space for water close to and in urban areas and to address the issues caused by water running off roofs, the surfaces of streets, car parks and paved gardens.

After heavy rainfall, everything that has been tipped down the drain ends up in our local waterways

Flooding events bring about an increase in levels of diffuse pollution in urban areas. In our towns and cities sewers overflow directly into rivers in extreme rainfall events - affecting river quality and storm ecosystems.  For example combined sewer systems, in which both foul water from sinks and toilets and storm water run off is carried in the same piping, are under severe pressure due to increased housing and people and a reduction of green spaces for absorbing rainfall.  They are often overwhelmed in periods of high usage such as periods of heavy rainfall.  

To cope with this overloading and to stop the dirty water backing up through our drains the system empties itself into a local river or stream when it reaches capacity, through a device known as a Combined Sewer Overflow or CSO. After heavy rainfall, everything that has been tipped down the drain ends up in our local waterways.

Household chemicals such as bleach and detergent, and products like cooking oil are not welcome additions to aquatic habitats – in extreme cases they can cause direct poisoning of wildlife as well as an increase in nutrients leading to reduced levels of oxygen in the water.

How we are helping

Creating and Managing Flood Storage Areas

Avon

Avon Wildlife Trust's Portbury Wharf lies on the land between Portishead and Royal Portbury Dock, adjacent to the Severn Estuary.  

Planning consent for the Port Marine housing development here was granted on condition that the developers designate a nature reserve on the adjoining land.

The habitats and wetlands act as a sponge, absorbing run-off from the development, filtering pollutants and providing flood protection in the event of a breach of the sea wall.  

It is used an example in Defra's best practice guide here (see page 46).  It is hugely enjoyed by the local community - see its webpage here. Image credit: Barbara Evripidou.

Cumbria

Cumbria Wildlife Trust manages the Thacka Beck Flood storage area just north of Penrith on behalf of the Environment Agency.  This area floods at times of high rainfall to attenuate the flow of the Thacka Beck, which flows under Penrith in a culvert.  You can see images of Thacka Beck on flickr (cpt Sim Reaney).

London

These schemes are fantastic for wildlife and many provide wonderful places for people to enjoy, as well as being successful at alleviating flooding

London Wildlife Trust is working to restore Crane Meadows, which lie to the immediate east of Heathrow Airport. The meadows are being restored to improve their water management capabilities and enhance the site for wildlife biodiversity: a win-win for local communities. About 30% of the site was formerly hard standing; about 20% of the site has now been restored to grassland.  Old meanders of the River Crane have been reconnected. The increased volume of the river coupled with the creation of high and low flow channels has increased the river's ability to store storm water, whilst still achieving great benefits for aquatic biodiversity. The 10% of hard standing that remains at the site is an old car park – and London Wildlife Trust is aiming to remove this, restoring it to soft landscaping and creating further enhancements to the reserve. 

London Wildlife Trust also has an on-going flood-management project called Lost Effra - named after a river - which is working with local communities on a water management strategy for Herne Hill in south London, an area which is prone to flooding. See the PDF below of its recent report A new way to manage water further below pp 32 - 54 for relevant information. Key recommendations on p. 66. London Wildlife Trust also published London: Garden City? which revealed the scale of the capital's garden loss - at the time of publication (2011) this was at a rate of two and a half Hyde Parks per year. Hard surfacing – including decking and paving – increased by over 25 per cent in the 100 month study period. Town gardens can do much to act as sponges and help stop water flowing too fast and prevent rivers being overwhelmed.

Lancashire

Lancashire Wildlife Trust has been working with the Environment Agency to design and deliver works at Lunt Meadows, a 70ha site.  The project involved diverting part of the flow of the adjacent River Alt through a system of ditches and reedbeds by lowering the embankment and installing a wind-powered pumping system at the outflow. It has restored floodplain connectivity to a channel that is predominantly embanked all of its length, which will improve the morphology and ecology of the River Alt catchment as well as improving water quality.

Creating reedbeds on site will allow filtering out of contaminants such as ammonia, phosphorus and tributyl tin compounds.  The scheme has brought flood risk management benefits to adjacent properties and the larger urban areas in the vicinity.

Yorkshire

Sheffield Wildlife Trust's Centenary Riverside plays a key role in Rotherham’s future.  Designed as a floodplain, it forms part of Rotherham’s Flood Alleviation scheme which holds back potential flood water and protects industrial and residential areas nearby.  

Yorkshire Wildlife Trust’s Potteric Carr wetland reserve saved hundreds of Doncaster homes from flooding in 2007.  During heavy rainfall, the water ends up in this flagship wetland reserve rather than flooding south Doncaster housing, before gradually soaking into the ground, and draining into streams and watercourses.  There are other benefits too.  A reed bed and aerobic filter (originally constructed to protect the reserve's wildlife from surface pollution) ensures that the water leaves the wetland cleaner than when it arrives.  And, as any visitor will tell you, Potteric's rare black-necked grebes, bittern, avocet, whooper swans, 15,000 golden plover and swarms of black darter dragonflies make it a fabulous place to unwind.  It's the ultimate win-win.

Semi-natural defences also help reduce surface flooding in towns and cities. One option, known as Sustainable Drainage Systems (SUDS), consists of engineered ponds and reedbeds, which are home to wildlife throughout the year; and larger basins which only fill up during prolonged periods of rainfall. A SUDS scheme at Manor Park in Sheffield saved a few dozen houses from flooding in 2007.

Shropshire

At Melverley Meadows nature reserve, Shropshire Wildlife Trust has worked on natural flood defence systems like the restoration of floodplain meadows, which alleviates flooding further downstream in Shrewsbury.

Sussex

Sussex Wildlife Trust is a partner in ARC – Arun & Rother Connections – an initiative which is promoting measures to prevent the Arun and Rother river catchments from flooding so badly.  After the heavy rains in January 2014, there was severe flooding in parts of West Sussex and the residents of Pulborough were particularly badly affected. The scheme is working to address the fact that 90% of flooding here comes from surface water run-off.  ARC is promoting rain gardens and Sustainable Urban Drainage Systems. They are going to be running community water events during 2014. See the download at the bottom of this page.

The North East

In the North East of England the Living Waterways Project is an EA initiative delivered by the North East Wildlife Trusts aimed primarily at reducing water pollution in urban areas and empowering community groups to take ownership of their local rivers.  But the initiative aims to produce multipurpose projects, integrating sustainable solutions to flood risk and improvements to river and riparian wildlife habitats.  The project is achieving its aims through a combination of community engagement, education and practical works, creating creation of reed beds and settlement ponds to remediate problems where they enter the river. 

All these schemes are fantastic for wildlife and many provide wonderful wild places for people to enjoy as well as being successful at alleviating flooding.

Downloads

FilenameFile size
sussex_wt_sky_garden_wetlands_can_help_stop_flooding.doc486.5 KB
a_new_way_to_manage_water_-_live_draft_feb_2014.pdf5.13 MB