Jonathan Morley
Associate Director - Hydrology
Cinderford Brook Fish Passage
Our hydrology teams undertook a hydraulic modelling exercise to support the design of fish migration barrier removal at four locations on the Cinderford Brook.
Key details
Project name
Cinderford Brook Fish Passage
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Client
Severn Rivers Trust
Location
Gloucestershire
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Services provided
- Low flows hydrology and hydraulic modelling
- Fluvial flood risk hydrology and modelling
- Input to river restoration design
Challenge
The fish barriers are sharp drops in bed level across the width of the channel which hinder upstream migration for key species. We needed to assess the hydraulic behaviour of the system to inform the design and measure the performance of the proposed barrier removal measures under low flow and flood low conditions.
The low flows analysis considered the range of required low flows for different species of fish. The magnitude of flow was estimated using LowFlow software which provided inflow conditions for four ‘mini models’ built in Flood Modeller Pro, each representing in detail a localised reach around the barrier.
For the high flood flows analysis, when the system is experiencing flood conditions (2-year, 20-year and 100-year including appropriate Climate Change Allowances), we conducted a linked 1D-2D model, covering the reach in which the four fish pass structures are contained. This checked the proposed measures do not have an adverse impact on flood risk.
Solution
Through assessing and comparing the existing ‘baseline’ scenario and the proposed barrier removal mitigation design, our modelling exercise showed that the proposed changes to the barrier removal design achieve continuity in hydraulic behaviour. Throughout the reach, it performs more uniformly and consistently, and the detrimental localised changes to flow conditions arising as a result of the barrier structures no longer exist.
Where the barrier used to be, the localised reach now behaves in a hydraulically similar way to the immediate wider up and downstream reaches, meaning the structure is no longer the potential cause of barrier to fish movement. The proposed barrier removal works represent an improvement to fish migration prospects on the watercourse.
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