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Loch Duntelchaig fish pass with CB Greenbox

Loch Duntelchaig fish passlogo scottisch water

Revolutionary technology and a large dose of innovative thinking are at the heart of a recently completed, cutting edge Scottish Water project. The installation of a new tilting weir fish pass has been critical in not only securing the water supply to customers in Inverness but is also protecting the migration patterns and survival of migrating fish passing through Loch Duntelchaig in Inverness-shire.

There were a number of challenges associated with this project, namely the tight turnaround time associated with the construction programme. The work had to be completed by the end of September 2014 – meeting this deadline was absolutely essential to ensure fish populations were not impacted due to construction work that could have prevented migration or the release of sediment into their habitat.

The utility’s project team used their expertise in the field of water resource management and embraced the latest technology to come up with a solution that would effectively meet both the business need to complete the job quickly, efficiently and cost effectively and the environmental needs of the migrating fish population. This came in the form of strong partnership working with a company that are promoting the benefits of ‘Greenbox’ technology and applying its capabilities to tilting weir technology.

The Greenbox is essentially an actuator, level sensor, solar panel, battery pack and control panel in a single, off-the-shelf unit which powers and moves the tilting weirs into the correct position, ensuring that fish passage can be maintained throughout the full operating range of the loch. It helped make savings in three ways; it removed the need for expensive cables to be laid or wind/ solar solutions installed to power the weirs, there was no requirement for the manufacture of a bespoke control panel and there was no need to use traditional actuators.

Caroline Olbert, from Scottish Water’s Water Resource Team, says the team faced many challenges: “Our task was to look at ways we could improve the security of supply to our customers in the Inverness area, as well as making an improvement to fish passage at the loch. We looked at a number of different solutions but none was as innovative and comprehensively beneficial as the one we settled on.”

“At the fish pass fixed concrete walls were replaced with tilting weirs that are adjusted to match the water level in the loch. Fish passes are often designed to work at particular water levels but at Loch Duntelchaig parts of the pass now move with the changing water levels, meaning that the pools and weirs are always at their optimum level to allow fish to move upstream. The inflexibility of the old fish pass meant that less water was available for use by customers during dry weather, as the loch had to be maintained at a higher level to allow fish to continue to use it.”

Control over the weirs came in the form of a Greenbox – a standalone unit, designed to sense water levels and adjust the position of the weir. These weirs were also custom built to include a V shaped notch to allow safe fish passage.

Hugh MacPherson, Scottish Water’s Project Manager for the project, said: “This fish pass is unsurpassed in terms of how innovative the technology behind it actually is. It is the first tilting weir fish pass of its kind in the UK and, possibly, Europe. Cost has also been a great win for the team in that the whole project would have been a lot more expensive if it hadn’t been for the Greenbox.

“A new standard has been set and the hope is that this concept will be replicated in the future at various reservoirs and lakes where the water levels fluctuate too much for a normal fixed pass.”