Pembroke Power Station Fish Deterrent System
To prevent fish from entering the CW intakes of the new Pembroke power station, an acoustic fish deterrent system was proposed.
The eventual design consisted of 18 submersible underwater speakers which could be lowered and raised onstainless steel guides mounted on a painted steel lattice frame standing on the concrete invert in front of the intakes, and fixed with saddle brackets to the concrete face of the intake structure. To allow access to the speakers acantilevered elevated walkway was required on top of the framework.
Due to access problems on the site itself, the installation work was carried out from the sea using a cranebarge c/w 50t hydraulic telescopic crane for the installation and a laydown barge c/w 25t hydraulic telescopic crane for storage and assembly of the components.
Firstly, the 9 main frames of the structure where bolted together. Each frame consisted of 2 vertical steel legs14m in height, to which the horizontal and diagonal cross bracing were bolted. Anodes were fitted to each leg as cathodic protection against corrosion, and the stainless steel guides bolted to the vertical legs.
With the 9 frames assembled, the heavy silt up to 3m deep had to be dredged by our own dive teams to allow installation of the frames. Starting at the centre of the structure, frame 5 was raised from the deck of the barge hanging vertically, and then slewed intoposition using the 50t crane. The frame was then lowered until the legs werejust of the invert.
The legs were then pulled towards the CW intake structure using chain blocks until the saddle brackets came into contact with the concrete bullnoses of the structure. Once the saddle bracketswere in contact, the frame was lowered into its final position ready for drilling and fixing to the concrete intake structure both above and below water.
With the middle frame successfully installed, frame 4 was lifted into position and secured against the structure. The infill steelwork between frames 5 and 4 could now beinstalled.
This process was repeated until all 9 frames and connecting infill steel work were installed.
The cantilever beams and decksupport steelwork could now be installed, along with the decking and handrailing for the walkway.
