Multi-disciplined piling solution at flagship Environment Agency scheme
Holmes Sluice spans the full width of the River Trent to help to protect Nottingham from flooding. Unfortunately, it is also a prime barrier to the natural migration of fish in the Midlands.
A scheme led by the Environment Agency to build a fish pass, the largest in the country at 215 metres in length, is designed to enable the bidirectional travel of fish by allowing them to bypass the sluice and swim freely up the river to reach their natural spawning and feeding habitats.
Ivor King provided both sheet piling and CFA bearing piles to this flagship £8.5 million project.
350 pairs of sheet piles installed to form fish pass channel
Two permanent sheet-piled retaining walls, running parallel to each other and connecting into the river at both ends, were installed to allow a channel bypassing the sluice to be formed.
The sheet piles were installed using Telescopic Leader Rigs with vibratory hammer attachments. Once in-situ, soil excavation between the two walls was carried out to allow the ‘fish elevator’ structure to be constructed.
The channel is 215m in length, 6.5m wide and variable depths of up to 6m, and is formed of 350 pairs of sheet piles.
CFA bearing piles provided for service bridges
Two service bridges, spanning the width of the channel to allow access to the sluices, have been constructed following the installation of a series of CFA bearing piles either side of the channel.
CFA piles are formed by drilling to the required depth using a hollow stem continuous flight auger. After reaching the designed depth, concrete is pumped through the stem as the auger is being withdrawn. A reinforced steel cage is then inserted into the fluid concrete.
Enabling access into site
Access to Colwick Country Park was via a weak bridge crossing a watercourse. However, the bridge was rated not strong enough to safely accept heavy goods vehicles and plant needed to build the fish pass into site.
A temporary bailey bridge was therefore constructed directly alongside the existing bridge to overcome this challenge.
We installed a total of 20 universal columns, of 11m in length so that a temporary span with increased load bearing capacity could be created to carry the heavy loads.
Providing better habitats for wildlife
Following pile installation and excavation of the main channel, a series of 20 ascending chambers have been added. Each is separated by a concrete stanchion, which also incorporates narrow slots for water flow.
All fish species, from salmon to coarse river fish, will be able to swim through the slots and rest in adjoining chambers, before continuing their journey through the pass and back into the river.