Case study:Gadebridge park river restoration

Project overview

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Status	Complete
Project web site	http://https://consult.environment-agency.gov.uk/engagement/gadebridge-park-information-page/
Themes	Environmental flows and water resources, Fisheries, Flood risk management, Habitat and biodiversity, Hydromorphology, Monitoring, Social benefits, Urban
Country	England
Main contact forename	Kelly
Main contact surname	Standbrook
Main contact user ID
Contact organisation	Environment Agency
Contact organisation web site	http://https://www.gov.uk/government/organisations/environment-agency
Partner organisations	Affinity Water, Dacorum Borough Council
Parent multi-site project
This is a parent project encompassing the following projects	No

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Project summary

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The River Gade, a globally rare chalk stream with poor ecological status within Gadebridge park, used to flow down a ‘perched’ channel created to supply water to Bury Mill. It was disconnected from its floodplain and over widened, leading to sluggish flows and a build-up of silt and vegetation. The EA Gauging Station Bury Mill and other in-channel structures acted as barriers to fish movement. Being disconnected from groundwater and spring flow had a significant impact on low flow resilience and to wildlife. Partnered with Dacorum Borough Council and Affinity Water Limited, this Environment Agency lead project diverted 415 metres of river channel to the valley bottom through the park. The Bury Mill gauging station was replaced with an ultrasonic one to allow fish passage. Work progressed from 2018 with construction complete in June 2025.

0.85 hectares of habitat was created, 3.9 hectares habitat enhanced, 6.5 km of river restored, 0.9 hectares buffer strip created and 1.1km water body opened to fish passage. The river corridor now provides better resilience to low and high flows and the impacts of climate change. Two new bridges and a large gravel access point to the channel were provided for the local community.

The project was designed by JBA Consulting Limited and delivered by BAM Nuttall Limited.

Monitoring surveys and results

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Macrophyte survey- August 2025: New species:

• Persicaria maculosa (Redshank)
• Callitriche obtusangula (Blunt fruited water starwort)
• Sparganium erectum (Branched bur-reed)
• Lemna minor (Duckweed)
• The total number of species has increased from 18 to 24 new ones

Increase in cover:

• Ranunculus penicillatus subsp. Pseudofluitans (Brook watercrowfoot)
• Veronica anagallis-aquatica (Water speedwell)

Fisheries: In a fisheries survey in September 2025, we recorded high numbers of minnow, and similar counts for stickleback and bullhead. Most significantly we recorded 14 trout in the ~100m section, with a few different age classes represented. We also undertook a detailed habitat survey to help assess how the habitat will change in the coming years.

Summary of improvement- In the 2021 survey we were suffering low flows. The highly modified old channel had no resilience in such conditions and offered very little habitat for fish during those flows. We confirmed this, as we recorded trout on a survey in 2022 further upstream, where restoration work had been carried out previously. Our work within the park restored a more varied range of habitats that could be used across more flows.

Our 2025 post works survey showed a significant increase in numbers of "minor" species, all of which are prey items for trout. Their increased abundance is a great sign of river health and will support trout numbers in the park. Habitat requirements change as trout are in different life stages. The trout we recorded were from a few different age classes, from juveniles to adults. This shows that even in a 100m section there is enough variety in habitat to support a population of trout.

BNG has increased by 10% from 26.8 units to 29.53 units

A Kingfisher and 3 Grey Wagtail have also been spotted on site since the restoration was completed.

Lessons learnt

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• Factor in a good contingency for the project, thinking about the contractors available on the framework, increases in material costs, inflation, FTE charges, compensation events. Have a good understanding of any changes to the design, working with the designer to estimate cost increases.
• The project group should contain members of the required level of authority. Set accountabilities early to avoid delays and misunderstanding plus each team's minimum requirements. Technical team leads should have ownership of their elements of the project to ensure all discussion items are logged and addressed.
• Make sure all staff have the training and capabilities to conduct their role within the project team and they have available resource.
• Develop a robust benefits realisation strategy early on to enable a better understanding of the benefits to all parties and a greater financial contribution.
• Walk the line of works with the Topography Plan and Tree Survey before commencing works at site, to check for mapping discrepancies.
• Ensure a close working relationship with the designer and the technical teams to avoid delays.
• Engage with the local community in a variety of ways eg. project web page, mailing list updates, project mailbox, Facebook, Twitter, council newsletters, onsite signage, community events.