Decades of development pressures and flood control measures had resulted in the channelization and degradation of Rye Brook in Ashtead Common National Nature Reserve southwest of London. Consequently, in 1999 the City of London, in collaboration with several stakeholder organizations, began planning a project to restore natural processes to the brook and improve riverine and wetland habitats in the Common. Construction activities focused on restoring meanders to the straightened channel and creating a network of ponds and scrapes that would provide hydrologic complexity and enhance habitat potential for aquatic and avifaunal species. With the assistance of local volunteers, project managers also constructed a flow-control “wall,” using metal-mesh gabion baskets, that is intended to limit the flow of water downstream and allow the periodic inundation of the river corridor. By restoring more natural hydrology to the watercourse, project planners hope to stimulate the recovery of biodiversity along the brook and create a pleasant, inviting atmosphere for local recreational users.
11 The Common, Ashtead KT21 2ED, UK, 51.32007468822239, -0.3108089523925628
Country or Territory:
Freshwater Rivers & Streams
Area being restored:
390 metres of river channel
City of London
Primary Causes of DegradationUrbanization, Transportation & Industry
Urban and agricultural development has had a negative effect on the Rye Brook, and a large portion of its natural catchment area is now occupied by housing. During the Second World War, a 365-metre stretch of the brook was straightened and channelised, and this alteration resulted in much-reduced biodiversity relative to other, more natural reaches of the watercourse. The Rye has gradually come to be seen as little more than a drainage ditch, and a number of surface-water sewage outfalls discharge into it along its course. Moreover, topographical surveys commissioned by the City of London in 2003 confirmed that the unnatural structure of the river channel and corridor reduce its capacity to hold water, making it particularly susceptible to flooding during periods of heavy rainfall.
Reference Ecosystem Description
The areas of running freshwater habitat within Ashtead Common (such as the Rye Brook, seasonal streams, and boundary and drainage ditches) support a variety of aquatic vegetation, including Fool’s Water-cress (Apium nodiflorum) and Curled Pondweed (Potamogeton crispus). The Rye Brook supports breeding populations of Minnow (Phoxinus phoxinus) and Three-spined Stickleback (Gasterosteus aculeatus). The Common Frog (Rana temporaria), Common Toad (Bufo bufo), Great Crested Newt (Triturus cristatus), Palmate Newt (Triturus helveticus) and Smooth Newt (Triturus vulgaris) are also known to be present in the network of ponds, streams and ditches. The Common is frequented by Adder (Vipera berus), Common Lizard (Lacerta vivipara), Grass Snake (Natrix natrix) and Slow-worm (Angius fragilis).
Within Ashtead Common, extensive areas of scrub grassland are frequented by a variety of songbirds, including: Blackcap (Sylvia atricapilla), Chiff Chaff (Phylloscopus sibilatrix), Garden Warbler (Sylvia borin), Lesser Whitethroat (Sylvia curruca), Whitethroat (Sylvia communis), Willow Warbler (Phylloscopus trochilus) and Yellowhammer (Emberiza citrinella). Of particular interest are Bullfinch (Pyrrhula pyrrula), Linnet (Carduelis cannabina), Redpoll (Carduelis flammea) and Song Thrush (Turdus philomelos). The woodland areas support Great Spotted Woodpecker (Dendrocopus major), Green Woodpecker (Picus viridis), Lesser Spotted Woodpecker (Dendrocopus minor), Little Owl (Athene noctua), Nuthatch (Sitta europaea), Sparrowhawk (Accipiter nisus), Tawny Owl (Strix aluco), Treecreeper (Certhia familiaris) and Woodcock (Scolopax rusticola), among others. Grey Heron (Ardea cinerea), Grey Wagtail (Motacilla cinerea), Kingfisher (Alcedo atthis) and Snipe (Gallinago gallinago) have all been recorded along the Rye Brook.
– To restore and sustain natural processes in the river channel
– To improve and safeguard water quality in the river corridor
– To enhance and sustain biodiversity
– To increase flood storage capacity and thereby improve flood management
– To provide an attractive, accessible and safe river for community enjoyment
– To develop stimulating opportunities for teaching and learning and encourage community involvement in the project
The project does not have a monitoring plan.
During the promotion and development of the project, the local community was kept fully informed of progress by means of presentations, public exhibitions, guided walks, displays, newsletter articles, press releases and the City of London’s website. As project managers were also keen to involve the Ashtead Common Volunteers in the project, it was decided that the flow-control structure should be designed to use materials that volunteers could handle, without the need for extensive training or specialized machinery. The end result is a “˜wall’ across the watercourse, built by the volunteers, with 36 metal-mesh gabion baskets filled by hand with 54 tonnes of limestone. It is a structure volunteers can feel proud of whenever they see it or walk over it for years to come. This kind of direct participation in the project has afforded community members many opportunities to learn about river and wetland development, and it promises to continue providing educational benefits into the future.
Description of Project Activities:
The City of London employed a river engineer to design a scheme that would reintroduce meanders to a 390-metre stretch of the river channel, lengthening it to 450 metres and creating the profile found in a natural watercourse. The new design was intended to encourage natural physical processes such as erosion, deposition of minerals and occasional flooding. To aid in the recovery of these processes and increase habitat diversity, contractors used heavy machinery to excavate a mosaic of ponds and scrapes (i.e. shallow pools) alongside the new channel, which will fill with water when the Rye floods over its banks. The improved wetland habitat and hydrological complexity afforded by these new features will enhance the entire river system. Hydrologic modelling conducted in association with this project showed that the relatively steep watercourse would not flood a significant length of the river corridor. Therefore, the project was extended to include a degree of positive flood storage, resulting in the construction of 250 metres of embankment across the valley using material excavated from the ponds and scrapes. A flow-control structure--built using 36 metal-mesh gabion baskets filled by hand with 54 tonnes of limestone--was built across the watercourse with a short culvert passing through it to limit flood flows passing downstream and thus inundate the ponds and scrapes more frequently. This will reduce the 1-in-100-year flood peak flow from 1.50 m3/s to 0.85 m3/s.
Ecological Outcomes Achieved
Eliminate existing threats to the ecosystem:
The restoration of the Rye Brook river channel in 2004 re-established the natural topography of the watercourse. The new meanders and network of ponds and scrapes can hold 2,500 m3 of water and will potentially allow 1.5 hectares of the Common to flood. The processes of erosion and deposition are gradually aiding in the creation of a natural diversity of river habitats, such as pools and riffles, and these enhanced freshwater and wetland habitats are improving the quality of the entire river system and supporting a diversity of wildlife. It is still early in the river's recovery, but already Common Darters, Southern Hawkers, Kingfisher and Grey Wagtail have been seen in the area since the project was completed in September 2004. Restoring the natural channel has, in turn, provided a connection between the river and its corridor once again.
Socio-Economic & Community Outcomes Achieved
Economic vitality and local livelihoods:
One key focus of the Rye Brook Restoration Project was the provision of an open space for the enjoyment of local community members. The design of the new river channel, with its ponds and scrapes, took into account the safety of visitors by replacing the steep sides of the old ditch with shallow banks and constructing a boardwalk with handrails on top of the new flow-control structure. These considerations ensure safe, easy pedestrian access over the site. In addition, a short length of all-weather-surfaced track will link the public footpath to this flow-control structure and will create a viewing point from which visitors can enjoy the developing wetland. Measures such as these are intended to provide for public recreation at the site and to imbue local community members with a sense of pride and ownership in the newly restored river.
Key Lessons Learned
The improved river corridor will play an important role in contributing to the abundance and diversity of both aquatic and terrestrial habitats on Ashtead Common National Nature Reserve. In addition, the Rye Brook will provide a natural corridor, linking areas of semi-natural habitats and helping to sustain healthy and viable wildlife populations. Enhancing the river corridor and its floodplain has also increased the flood storage capacity of the Common by reducing the level and flow-rates of water in the main channel of the Rye Brook during peak flows and providing some flood alleviation for nearby residential properties. The lower flow-rates will reduce the risk of wildlife being washed away and will ensure the storage of floodwater on the Common, thereby providing additional wetland habitats. Improved biodiversity, resulting from the creation of new aquatic and terrestrial habitats in the river channel and corridor, will be enhanced further as the maturing habitats are colonised by a variety of flora and fauna.
A smaller restoration project is now in the planning stages for 2006, to take place on a section of the Rye Brook adjacent to the area restored in 2004.
Sources and Amounts of Funding
SITA Environmental Trust, through the Landfill Tax Credit Scheme, provided Â£35,000 towards the river restoration project on Ashtead Common. The City of London was also successful in obtaining funding from Thames Water, Surrey County Council, and the Mole Valley District Council. Altogether, this financial support constituted 50% of the total project costs, which was then matched by the City at no cost to the local community.
The City of London Open Spaces Department
Ashtead Common Estate Office
Woodfield Road, Ashtead, Surrey KT21 2DU
Tel: 01372 279083
Fax: 01372 271670