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P&S Consulting Engineers

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Projects » Poaka Beck

The project required the replacement of an existing siphon pipeline situated just under the surface of the upstream face, crest and downstream face of the Poaka Beck Impounding Reservoir Dam, near Ulverston, Cumbria. The siphon pipeline has a dual purpose, serving as the supply pipeline to Poaka Beck Water Treatment Works (WTW) about 800m downstream and as a scour pipeline for lowering impounded water within the reservoir in an emergency situation requiring partial reservoir drawdown. 

The project required the replacement of an existing siphon pipeline situated just under the surface of the upstream face, crest and downstream face of the Poaka Beck Impounding Reservoir Dam, near Ulverston, Cumbria. The siphon pipeline has a dual purpose, serving as the supply pipeline to Poaka Beck Water Treatment Works (WTW) about 800m downstream and as a scour pipeline for lowering impounded water within the reservoir in an emergency situation requiring partial reservoir drawdown.

The siphon arrangement comprises:-
A submerged ‘bellmouth’ inlet structure in the upstream face of the dam with a hydraulically operated isolation valve.
An inclined siphon pipeline to an air vessel chamber in the dam crest containing equipment for initial priming of the siphon and for automatic extraction of air as it accumulates at the top of the siphon during operation.
An inclined siphon pipeline in the downstream face from the air vessel chamber to a valve chamber in a berm in the downstream face of the dam containing a hydraulically operated valve for use during siphon priming
An inclined siphon pipeline from the berm chamber to a downstream tee with one leg to Poaka Beck WTW and the other leg to the stream for use during scour operations or drawdown.
The project consisted of the complete replacement of the siphon pipeline with a polyethylene pipeline, air vessel chamber and berm chamber.

PaSCoE were commissioned to provide both permanent and temporary works designs including:

  • Holding down blocks for new pipework;
  • New reinforced concrete access steps;
  • Geotechnical Advisor, supervising dam excavations and compaction of new clay core;
  • Dam stability assessments for plant access on berm track and dam face.

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