Finding the balance of fish pass design

The Construction (Design and Management) Regulations (2015) places a legal duty on Designers to eliminate, reduce and control foreseeable risks that may arise during the construction or maintenance of a building, product or system. For a technical fish pass, there is a requirement to optimise the pass for fish passage. This must however be balanced against other site-specific constraints and the need to minimise the risks associated with constructing and maintaining the fish pass. Finding the balance between performance, maintenance and any other site-specific constraints is the crux of fish pass design.

Principal Designers plan manage, monitor and coordinate health and safety in the pre-construction phase (and beyond at the client’s request). Our team of hydroecologists, civil engineers and principal designers are experienced at working together to produce designs which form a balance between the hydraulic performance, consideration of health and safety and other site constraints.

Close integration of our principal designers in the project team at all phases leads to fish pass designs which are optimised from a technical, construction and health and safety perspective.

Langsett fish pass

At Langsett in the upper reaches of the River Don near Sheffield, the hydrology of the river dictated that the proposed Larinier fish pass needed to be narrow (<0.5m) to function across the whole flow regime. This however meant that such a narrow pass would effectively become a 20m long confined space, and potentially hazardous to maintain.

Ease of access had to be balanced against public safety as the pool downstream of the weir is a popular bathing spot in summer. Following an options appraisal process where a number of options were considered, a walkway was added to the side of the Larinier to enable safe access to the pass for maintenance.

Lobwood fish pass

At Lobwood weir on the River Wharfe, the river is flashy in nature, with floods likely to overtop any fish pass and access steps a number of times a year. Debris loads in the river are also likely to be high as the river upstream of Lobwood is bounded by deciduous woodland.

Any railings or access paths to the pass are therefore highly likely to be damaged during these frequent moderate flood events, and require cleaning from debris snagged on the railings (increased maintenance). A large access platform was incorporated into the design which allowed debris removal from the pass to be undertaken form the bankside via machine (this also largely removed the need for man entry into the pass). Removable handrails were included in the design, to be implemented before maintenance and removed following maintenance to reduce the risk of damage by debris.

Want to know more?

Email Dave Mould for more information or visit our fisheries web page.

Are you attending the River Restoration Conference on 24-25 April? We’ll be showing you how our catchment and river restoration team deliver innovative and sustainable solutions to improve our rivers and catchments.

We are giving four presentations and have eight posters for you to see our project examples. Read the abstracts to find out more in our interactive guide below.

Leave a Reply