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3.25 km of chalk stream habitat made passable to fish
12 brown trout caught and successfully transported to the new channel
Rare black poplars and aquatic plants introduced
The Chalgrove Brook, a rare chalk stream boasting a population of wild brown trout, faced a critical situation.
Classified as "failing" for fish under the Water Framework Directive, the presence of barriers and obstructions emerged as significant factors impeding the resilience and abundance of fish populations. This project, located near the historic Stadhampton Mill, aimed to address a concrete weir which was obstructing fish passage and causing various ecological challenges. Barriers like this redundant weir negatively impact river ecosystems by isolating fish populations, hindering natural spawning, disrupting sediment transport, and affecting water quality.
Thanks to funding from the Environment Agency (EA) Water and Environment Investment Fund (WEIF), the Stadhampton Mill Fish Pass project was launched to address these issues.
The primary objective was to create a bypass channel that would enable fish to navigate past the old weir, thus opening up approximately 3.25 km of vital chalk stream habitat for brown trout and other species.
The project began in March 2023, with the excavation of a new 1.2 km fish passage channel and infilling of the existing channel.
The new channel followed a more natural route, utilising a paleo channel adjacent to the straightened man-made channel that existed prior. The banks of the channel were graded to create a low gradient bankside, facilitating diverse vegetation growth.
To safeguard brown trout population during construction, before infilling the existing channel, the Environment Agency and dedicated volunteers moved fish from the existing channel into the new one using hand netting and electrofishing.
During this process, 12 brown trout were caught and relocated into the new channel.
The bypass channel was carefully designed to ensure that fish of all species, ages and sizes can pass whilst also seeking to provide valuable ecological habitat.
The bypass channel was designed to provide passage across a wide range of flows. The channel features 14 rock weirs with offset notches which create a series of drops small enough to enable fish passage. The bed of the channel utilises the pre-exisiting floodplain gravel, which was exposed during excavation, and provides the ideal basis for reestablishment of characteristic chalk stream communities.
A series of measures were taken to assist the establistment of characteristic riparian and aquatic plant species and protect them from grazing.
After construction was complete, the newly excavated river bank was seeded with native species. Two rare black poplar trees, one male and one female, were also planted along the bank of the new channel. Hedgerow species like hawthorn and alder were planted to promote connectivity with the existing tree line. Aquatic and emergent species of local genetic origin, carefully selected with the assistance of Rick Bennet of Babylon Plant Nursery, were sourced and planted by volunteers. Species included water crowfoot, water parsnip, water forget me not, and yellow flag irises. Chestnut post and rail fencing was installed to protect the new channel from horses which graze in the adjacent fields.
Our Funders: Environment Agency
Our Partners & Suppliers: Amenity Water Management, 5 Rivers, Babylon Plants Nursery, the landowners and our dedicated volunteers
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