- 25th May 2017
- Posted by: Joanne Woodhouse
- Category: Projects
In 2015, the River and Fisheries Trusts of Scotland commissioned us to produced detailed designs for the removal of Dowies Mill weir. They also asked for a technical solution to replace an existing fish pass at Fair a Far weir on the River Almond, Lothian. This would facilitate the passage of salmonids, lamprey species and eels.
At these locations, the Almond is considered an active, high energy, bedrock influenced river with a Qmean of approximately 6.0m3/s. The head difference across Fair A Far weir at Q95 exceedence flow is approximately 3.5m.
Heritage and access considerations were particularly challenging at these sites. Both sites are within a designated public open space. The left banks are designated as a Designed Landscape and an Area of Outstanding Landscape Quality in Local Policy.
Fair A Far weir and mill remains are designated Category B. Therefore they are protected under the Planning (Listed Buildings and Conservation Areas) (Scotland) Act 1997, and are located in the Cramond Conservation. A pre-existing pool and traverse fish pass sits between Fair A Far weir and the inaccessible left bank. The bank consists of a near vertical, 20m high, sandstone face.
Dowies Mill weir is adjacent to the highly valued River Almond Walkway, an accessible footpath which is busy during the summer. Dowies Mill lies 300m downstream of the Category B listed Cramond Brig.
A further challenge has been to develop a solution that is aesthetically acceptable in the context of the adjacent landscape and heritage receptors of value. It needed to reflect the visualisations used in earlier public engagement activities as far as possible. It also ideally needed to overcome the large head difference at the weir which sits within the footprint of the existing fish pass.
At Fair A Far weir, our project team is designing a two flight Larinier fish pass with an adjacent dedicated eel & lamprey pass.
At Dowie’s Mill, the solution is full removal of the weir. This is in combination with bed stabilisation and creation of a boulder-rapid arrangement.
The proposed Larinier solution at Fair A Far results in a fish pass whose geometry and hydraulic performance achieves all associated criteria for large migratory salmonids, as specified in the EA Fish Pass Manual.
Furthermore, our engagement with the Scottish and English regulatory fisheries specialists enabled acceptable, compact changes in direction to be incorporated into the resting pool design. This ensured the alignment and location of the pass also achieved accepted technical criteria relating to fish passage.
We utilised 3D CAD software in development of the design. This facilitated rapid and ongoing visualisation of features key to the technical performance of the design. This did however have the potential to compromise the aesthetics of the scheme. This facilitated the most appropriate JBA technical specialists (heritage & structural engineers, fish pass specialists), as well as the client group, being efficiently involved in the design decision making process. This technique was particularly useful in resolving design decisions relating to appropriate construction materials and general arrangement details.
Want to know more?
Find out more about the work our fisheries team does in our environment section.
You can also contact Jon Whitmore for more information on this specific project.