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Hull and high water

Cleaning up the muck spewed out from Hull is, at £200M, the biggest single project in Yorkshire Water's current portfolio of work. Labelled Humbercare, the wastewater scheme will collect sewage from three existing works via a £50M tunnel and convey it to a £54M treatment works before discharging clean effluent to the sea.

Driven by the Urban Wastewater Directive, it will be a big improvement on Hull's present arrangements and incomparably better than the original Victorian sewerage system.

Hull's first mains drainage relied on the tide. Very large brick sewers were constructed under relatively small streets near the sea wall. They acted as tanks, storing up whatever flowed through the drains so that at the appropriate moment the contents could be pumped over the sea wall so that the tide could, hopefully, carry it away. Only minimal screening has been added since.

In the 1980s the Department of the Environment set the limit of the Humber estuary at the Humber Bridge. This meant Hull's sewage discharge was obliged only to undergo primary treatment. Later a judicial review changed the definition of the estuary as beginning at Spurn Point, therefore requiring only secondary treatment.

The initial plan for the project involved a relatively small sewer tunnel at high level. Value engineering and reappraisal of the scheme with the contractors led to construction of a much larger and deeper sewer tunnel.

Siting the tunnel deeper reduced disruption on its 13km route across Hull and the 3.5m diameter accommodated stormflow storage within the sewer. The Lovat earth pressure balance tunnel boring machine driving through alluvial sands and gravels is now three quarters through the work.

Treatment works design and construct contractor Kvaerner is founding every structure on piles at the site, formerly an old timber yard located east of the city. At the shore the outfall is short because of the high standard of treatment at the works. In consequence it is being built inside a relatively small cofferdam.

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