Precast concrete offers many advantages for the construction of fish passes as the material is both hard wearing and will not corrode in water. Working within watercourses can often be challenging and costly, with both the environment and the safety of your workforce a key consideration. Precast concrete can help reduce both the risks and the costs of the project.
A precast solution for fish passes offers many advantages over insitu. As the units are manufactured off site time delays due to poor weather are reduced. Installation times will therefore be minimalised which will reduce the construction costs for the project. All the units will be identical and there will be less wastage involved as well compared with using shuttering and wet concrete.
There are a number of different types of fish pass or fish ladder that can be installed, one of the most common being the Larinier. These are often chosen because they are suitable for several different species of fish and it is possible to design the width and height of the baffles according to the flow rate needed. With the Larinier, rest pools can be incorporated in between flights, allowing fish to ascend in stages. In the same way, a pool and weir fishway or fish ladder consists of a number of overflow weirs and pools and is constructed in the form of a staircase, enabling fish to jump from one pool to the next. A vertical slot fish pass replaces weirs with walls and instead has vertical slots or gaps allowing fish to swim from one pool to the next without the need to jump to reach upstream. This is particularly suitable for large numbers of migrating fish.
In the UK, the Environment Agency is the primary agency involved in both the legislation and advice on the construction of fish passes. Statutory responsibility for the approval of fish passes for migratory salmonids lies with the Environment Agency under the Salmon and Freshwater Fisheries Act 1975 (‘SAFFA’). Plans for the fish pass must be approved by the EA who will review the designs before approval is given.
The Environment Agency produce an excellent Fish Pass Manual which includes guidance on the legislation, selection and approval of fish passes in England and Wales and this can be found here: FISH PASSES (publishing.service.gov.uk)
Poundfield Precast have considerable experience in using low and ultra-low carbon precast concrete and this technology can be significantly important in environmental projects such as fish passes and fish ladders. In 2023 it is expected that over 50% of the projects the Precast Products Group (PPG) are involved in will fall under the Greenbloc low carbon alternative ranges.