The Cockshut Stream
Restoration Project
Restoring, revitalising and protecting.
The Cockshut is a 3km long chalk stream that flows from springs at the foot of the South Downs in Kingston, eventually joining The River Ouse before flowing out to sea. The restoration project realigned the stream into a new channel flowing through 6.8 hectares of wetland habitat, boosting the biodiversity and climate resilience of the Lewes Brooks habitats and beyond. The reserve helps with flood management and carbon storage, but also allows the stream to flow naturally, unpolluted and with its native plants and wildlife protected.
The Cockshut: A Rare and Special Habitat
Only 200 chalk streams are known globally, 85% of which are found in the UK in southern and eastern England. They are a haven for iconic species like otter, kingfisher, brown trout and mayfly as well as many fish and specialist invertebrates on which they feed.
Since chalk is porous – like a sponge – rain that falls on the hills drains through the ground into aquifers and raises the water table. Once the water levels reach a certain point, water flows out from springs and into the chalk streams. The filtering action of the chalk means they generally have clean, clear water and more stable temperatures.
Often made up of natural gravel and flint, chalk stream beds are good spawning areas or fish and breeding grounds for freshwater invertebrates. The streams also provide a good habitat for a wide range of river plants like water crowfoot.
Prestigious Award Winner
Cockshut Stream Restoration won both the Landscape Category and the People’s Choice Award at the South Downs National Park 2024 Design Awards: 2024 Design Award Winners - South Downs National Park Authority
Chalk streams sometimes have winterbourne stretches in their headwaters, which run dry in late summer or autumn as the springs stop flowing. These are known as ephemeral chalk streams and those that flow all year are known as perennial chalk streams
What you can see
Look out for kingfishers, snipe, egret and herons in the grassland. Toads, sticklebacks, eels can be spotted in the scrapes and ponds. Grass snakes use the reedy ditches, and many species of dragonfly can be seen patrolling the meadow and river banks.
Flood Management
The site is designed to provide benefits during periods of both heavy rainfall and prolonged dry spells. With an additional 16,000m³ of water storage available within the footprint of the site it reduces peak flows reaching Lewes by up to 90 minutes and adds to both local and landscape wide flood mitigation measures being delivered to reduce the risk to Lewes.
During periods of dry weather then water levels recede into a meandering channel connected to low lying sections of the floodplain to create a functional wetland which can support freshwater species during periods of drought. As a SSSI designated for its freshwater ecology it was critical to the projects outcomes that the habitat created was resilient our changing climate.
The Idea
In 2019 the idea for the Cockshut Stream Restoration Project came about after representatives from Lewes District Council, the Ouse and Adur Rivers Trust, the South Downs National Park Authority and the Environment Agency went for walk to look at opportunities to improve the Chalk streams that run through Lewes. The two streams, namely the Winterbourne and the Cockshut streams, have been moved and canalised over time providing poor aquatic habitat. The land behind the Stanley Turner Ground was identified as having potential to create a wetland area - and so it began!
The Plan
Driven by the Ouse and Adur Rivers Trust’s (OART) vision to develop a rich and diverse environment which supports a range of wildlife species and inspires individuals and communities to engage with and protect their local river systems OART and LDC contracted cbec eco-engineering to develop a detailed design option for the restoration section, taking into consideration the local constraints of the site, such as the downstream tie in point, existing services, and the requirement to not increase flood risk to the adjacent properties. cbec project - The Cockshut Realignment Project
Historical management of the land surrounding The Cockshut required the construction of the channel to help with management of drainage of the surrounding marsh land, diverting flows from upstream and capturing surface water runoff from the land between Lewes town and the channel, in the area that is now the playing fields. Managing flows and draining the marsh land allowed the development of the land for agricultural purposes
Construction works commenced on the 5th of June 2023. The contractors first job was to strip off the existing vegetation and stockpile the material for use on site later. Next they cut out the main channel that would allow the stream to meander through the site.
OART and Lewes District Council (LDC, principal landowner for the site) sought to implement restoration measures which help improve morphological and ecological conditions in the channel and the surrounding land area, recognising that The Cockshut is an artificial construction but that drainage of the site is still required. To achieve this goal desk and field-based assessments were undertaken, then initial and detailed design development for the site and the hydraulic modelling results comparing flood risk for existing and design conditions Engineering drawings for the final design were then developed.
Breaching the banks
On the 9th of August 2023 the banks for the Cockshut stream were breached allowing the water to flow into the newly created wetland. The water levels will need a low level of management in the future to ensure the right amounts of water are heading down the stream and down the Celery Sewer.
