Environment | Supply Chain|
Excavation of channel
for giant fish pass underway
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Work to dig out the channel for the country’s largest fish pass is well underway.
These images offer a both bird's eye and a fish's eye view of a structure the Jackson team is constructing on behalf of the Environment Agency at Colwick Country Park in Nottingham.
When it is finished, the main channel will be 215 metres long, 6.5m wide and a vertical depth from ground level to invert that varies from 4-6m - providing access around Holme Sluices to scores of fish species migrating upstream on the River Trent including the critically endangered European eel.
Using an 35T and 3T excavator, the channel is being dug out at 6m per day. A cofferdam is in place to ensure no water enters the channel until work there is complete and will become part of the main permanent channel structure.
Views of the fish channel excavation underway at Colwick (2)
Pools
The next phase of work in the channel will be the construction of the reinforced concrete floors, walls and 20 ascending pools, which will all be cast in situ. The water flows within the channel will vary between 4.4m3/s and 4.9m3/s.
The 20 ascending pools provide rest for the migrating fish whereby the flows will drop to 1m3/s in these areas. The pools also act as multiple hydraulic breaks to control the level of water within the channel due to the circa 3m head between upstream and downstream river levels and therefore not affecting the Environment Agency’s legal requirement to maintain navigation levels in the upstream River Trent.
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Piling
Piling for the main channel took place between April 2022 and August 2022 and was overseen by Jackson’s supply chain partner Ivor King Piling who installed circa 350 pairs of AZ36-700 sheet piles to create the cofferdam for the main channel works with piling depths ranging from 8m to 11m.
To aid in the installation of the sheet piles due to the geology of the site (as it sits on a mudstone strata at approximately 7m below ground level), the full 400m circumference of the sheet piling cofferdam was pre-augured. This allowed Ivor King to install between 20 and 25 piles during piling days.
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