River Rother Meadowgate regulator and fish pass, UK

The UK’s Environment Agency has procured the world’s first full-width modular fish pass using NEC. The innovative structure was built as part of an £8 million upgrade to the River Rother Meadowgate flow regulator in Rother Valley Country Park near Sheffield. The project won the Innovation Award at the Constructing Excellence Yorkshire and Humber 2025 annual awards and was highly commended for the Innovation Impact Award at the 2025 British Construction & Infrastructure Awards.

The Environment Agency engaged contractor JBA Bentley under an NEC3 Engineering and Construction Contract (ECC) Option C through its £2.5 billion 2013−2019 NEC-based Water and Environment Management (WEM) framework in 2018. Work started on site in February 2022 and was completed in October 2024.

Meadowgate is part of a wider scheme, the Don Regulators, to upgrade three river flow regulators on the River Rother, which aim to attenuate flows on the Rother and protect downstream communities on the River Don. The Meadowgate project involved replacing the life-expired bottom-hinged regulator gate with a top-down, vertical control gate and improving passage for coarse fish, eel, trout and salmon. The new gate was completed in November 2023 after which the UK’s largest temporary syphon solution was installed to create a dry riverbed immediately downstream on which to build the new fish pass in June 2024. 

Consisting of four 1 m diameter steel pipes 110 m long, the syphon system passively diverted up to 12m3/s flows around the working area for the three-month construction programme, saving over 1000 t of carbon dioxide emissions equivalent compared to a traditional diesel-powered over-pumping solution. Eighty 2.5 m by 2 m precast concrete ‘fish tiles’ weighing 4 t each and with varying height upstands were then installed across the reformed riverbed. These were designed using computational fluid dynamics to ensure bottom flow velocities remained below 1 m/s and a minimum depth of 0.2 m.

NEC project manager Arcadis was appointed under an NEC3 Professional Services Contract (PSC) through the Environment Agency’s Commercial Services Framework.

Collaborative delivery 

Environment Agency project manager Tim Cobb says NEC3 ECC Option C was used because it was the standard construction form under the WEM framework, which has since been replaced with its NEC4 based Collaborative Delivery Framework (see case study). ‘We’ve used NEC contracts for a number of years now as they are the best and most collaborative way for delivering engineering design and construction contracts.’
He says a particular collaborative benefit of NEC is the ability to allow early contractor involvement. ‘JBA Bentley was engaged to undertake surveys and assessments of the existing regulator gate and then develop the design and support the Environment Agency writing the works information for the refurbishment and replacement project.’ 

JBA Bentley civil engineer Saffron Catterick says another example was the early engagement with fish tile supplier Craven Concrete. ‘Early involvement allowed the team to co-develop and approve custom moulds, driving the fish pass tile design and ensuring accuracy, buildability and construction readiness. Regular visits by the design lead to Craven’s premises maintained strong communication and reduced production risk.’

She says the project team adopted a collaborative commercial approach to align programme objectives and foster shared accountability. ‘Milestone dates were agreed collaboratively, with delay damages balanced by appropriate risk allocation. The largest risk for all parties was flood risk, with the team ensuring the works did not increase flood risk in the surrounding area and that temporary works were safe for operatives in the channel. After identifying this risk, the parties agreed this would be held by the client.’ 

Catterick says the project team co-developed the works information to add a trigger level for river levels and flows. ‘This was effectively managed through an innovative flood forecasting application providing a 48-hour lookahead, text alerts and data validation. When unusually high flows were confirmed, a compensation event was triggered. This collaborative approach to risk allocation, supported by the ECC Option C pain-gain share mechanism, promoted joint responsibility and efficient, goal-aligned delivery.’

Keeping on time and budget

Arcadis associate project manager Phil Boyes says proactive use was made of NEC early warnings by both the contractor and project manager. ‘Early warning meetings focused on mitigating the issue and identifying who was best placed to carry out the mitigation to minimise project impact.’

He says for significant change items, compensation event meetings were held prior to the submission of compensation event quotations and programmes. ‘This allowed the contractor to explain the pricing and programme logic, minimising assessment questions and leading to prompt agreement and implementation.’
Boyes says an example was the significant change in the fish pass design and temporary works required for it. ‘The contractor presented a number of options detailing the cost, programme and risk implications, allowing for collaborative discussion and the best option to proceed with.’ 

He says programme submissions included detailed supplementary documents to assist in identifying and understanding changes and progress. ‘This simplified the programme review and assessment and acceptance process, which led to no issues delivering the project in compliance with the programme.’ 

Boyes adds that the project manager updated the project budget forecast to completion on a monthly basis, ensuring it always reflected the latest programme at the time of submission. ‘The assessments included monthly comparisons of forecast and actual defined costs, including understanding what drove any changes and implications for spend going forward.’

Benefits of using NEC

• NEC provided the best and most collaborative way to deliver the design and construction, including allowing for early contractor involvement.
• NEC pain-gain share promoted joint responsibility and efficient, goal-aligned delivery.
• NEC early warning process helped to identify who was best placed to carry out mitigation to minimise the project impact.
• NEC compensation event process ensured the contractor was fairly and quickly compensated for changes to the works information. 
• NEC programme submission and acceptance process ensured the project was delivered to the agreed programme and budget.