TPA helped Mott MacDonald Bentley with a walk on the wild side

08 Dec

Modular pontoons helped to reinvigorate a reservoir draw-off tower.

A project to renovate a draw-off tower in the middle of a Welsh reservoir, using plastic and NATO steel pontoons supplied by specialist temporary access solutions provider TPA, has now been completed.

Main contractor Mott MacDonald Bentley (MMB) started work at Llyn Brenig near Denbigh in Conwy, North Wales, in August 2018 to replace a permanent 10-tonne gantry crane on top of the concrete structure.

TPA installed a 250m2 modular plastic pontoon with handrails and access gates as a temporary jetty providing access for operatives onto the water and mooring for the vessels and steel work barge working on the project.

The VP plc company also supplied six 2.1m by 4.75m steel NATO pontoon sections to create a 6.4m x 9.5m work barge with handrails. With a maximum load capacity per m² of 465kg, this is being used to float and manoeuvre equipment and materials across the water, including three seven-tonne steel gate valves (6m high by 2.8m wide) to the reservoir crane tower where they are lifted off and secured into position.

The concrete draw-off tower was first installed at Dŵr Cymru Welsh Water’s showcase reservoir in the blazing hot summer of 1976. Standing some 50m tall, but with only one to two storeys showing above water level, it has a 330m tunnel to the base of the dam. 

But the extreme environment has taken its toll and as part of the work to secure the new scour gates into position within the existing tunnel, new hydraulic concrete profiling was installed. The concrete for this was transported over in a skip by crane on the NATO work platform pushed by a 90hp RIB.

The project has seen perhaps more than its fair share of bad weather, with high winds causing the jetty pontoon to rail against its moorings. This required TPA to redesign the layout to give two, rather than one, “leg” between the pontoon and the shoreline, for extra security.

MMB site manager Dewi Strawson said: “We work on reservoirs all the time but this one was fairly unique. There aren’t many that have a 10-tonne crane in the middle.

“We were working in an exposed location and were hammered by the weather at times but TPA reacted well to any issues. They came out quickly to sort them out.”

TPA’s NATO steel pontoon sections were lowered into the water, then pushed together and coupled by connecting forks and rings. This method of assembly only requires up to three people so floating work platforms with different dimensions can be built very easily. 

As well as being attractive to birdwatchers (the lake is home to ospreys), cyclists, fishermen, sailors and walkers, Llyn Brenig has a Discovery Centre with a fully-equipped indoor classroom and outdoor area where schools can take part in hands-on activities that include the water cycle, water efficiency, climate change, pond dipping and orienteering.