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Martin's blog: sewer flooding is a major issue

My view is that a good deal of underground drainage systems are going to be severely challenged in future if UK is now to experience frequent intense rainfall as we have seen recently.

Martin Knights is president of the International Tunnelling Association

Existing and aged drainage systems were never designed to take the extra runoff from areas that have been surfaced over let alone increased run off within the zone and purpose that they were intended. Countries that traditionally have traditionally experienced regular intense rainfall have adapted their drainage systems to suit.

In Houston wide channel networks quickly direct intense storm water runoff and in South East Asia in Malaysia for instance their recent infrastructure improvements recognise the need for directing and storing large volumes of surface run off away from potential flooding of urban areas.


The biggest area of concern in UK will be legacy sewerage networks that have combined storm and sewer capacity. During intense rainfall the combined contents of the network usually overflow into rivers causing unsightly and disgusting 'slicks'. A number of UKs drainage systems exist on this principle which the water companies will have to address. Cities such as Glasgow, London, Liverpool, Leeds and Newcastle to name some may have to face up to this climate change issue at some cost to the water company customers.

The Thames Tideway scheme is a response to this requirement. Thames Water have been investigating options for a number of years and are now about to impliment a £2bn tunnel/CSO scheme in two phases to prevent frequent overflows of combined stormwater/ sewage into the Thames. The proposed tunnel will collect overflows and direct them via a dedicated spine tunnel under the Thames from Hammersmith to Beckton treatment work. Scottish Water are looking at a tunnelled options for a scheme designed to prevent serious future potential flooding of the city areas as has been recently experienced. Cardiff, Bristol and Blackpool have all undertaken schemes in recent years so the indications are there that existing major infrastructure may also require upgrading to meet the climate change related challenges.

A recent article in the Economist related the effects climate change on glacial melt inPeru.Andean hydro schemes that were powered by once reliable water supply cannot now operate because cycles of flood/drought and render existing power plant redundant. Although not directly connected to the context of this article it does demonstrate that the irregular aquatic effects of climate change are a very serious challenge (and opportunity) for civil engineers. The sustainable opportunity may be in harnessing and storing the intense runoff and reusing it rather than draining away back to rivers/seas.

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