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Glasgow drain brains

Water and drainage Sustainable drainage

'Joined up thinking' is the watchword for Glasgow's new strategic drainage study, says Adrian Greeman.

It was when monsoon level rains hit Glasgow in the summer of 2002 that the trouble started. Sewer overflows in the unprecedented downpour meant foul water debris in the streets added to the misery of severely disrupted transport systems and more than 500 flooded homes and businesses.

The first reaction, once the authorities had pitched in with sandbags and emergency pumps, was to 'find the guilty';

the obvious target was Scottish Water, blamed by press and politicians for an inadequate sewer system and bottleneck drainage. Sure enough the sewers, which have not been significantly expanded in capacity for decades, were part of the problem.

'There is a backlog of investment and money has tended to go on treatment works and processing, which is good, ' says David Wilson, senior strategist for Scottish Water and a key figure in subsequent development plans.

But it soon became clear there was more to the story.

Cluttered surface water channels, increased run-off from ever more paved areas, choked culverts and the sheer volume of some 'overland flows' all contributed to the problem.

'Like most older systems, ' says Wilson, 'storm flows are taken into a combined foul and storm water drainage. It does cope normally.' 'Except when it rains.' adds Iain Macnab, development manager for Glasgow City Council's development and regeneration service.

His council is responsible for flood prevention under Scottish law. Like the 31 other local councils in Scotland it must control and maintain the above ground streams, burns and drainage channels, either directly or by instructions to private landowners where watercourses run. The Scottish Executive approves bids and funds work.

So the storms of July 2002, which dropped more rain on the city than even the current 100 year design event calculates, were a wake up call to both parties.

'It all came at the right time really because there was already a growing realisation of a need for action, ' says Macnab.

Flooding has been quite regular in Glasgow and needs to be dealt with; and the city is particularly interested now because of major regeneration plans it has for several rundown areas of the city including the eastern side's Dalmarnock. This area of old disused steelworks and other industry was worst affected by the flooding. Now some £1,500M worth of potential public and private investment is pending to regenerate wastelands.

Glasgow council responded hesitantly and then with growing enthusiasm to proposals led by Wilson that a joint strategic study be carried out.

He felt that rather than the city spending three years assessing the burns, gullies and run-offs of the once natural system, while Scottish Water looked at the underground sewerage, the two could work together.

Scottish Water funds the studies but benefits from potentially reduced hard investment.

Not only is duplication of effort reduced but changes on the upper system can to be tied to the underground; if a cleared channel above could take flows then capacity could be reduced beneath.

An integrated study is better able to take in new techniques in sustainable urban drainage systems (SuDS), says Norman Fleming from civil engineer Hyder which Scottish Water has appointed as lead consultant for the strategic study.

Fleming, who is project managing the technical input to the study, says there is huge scope for this in Glasgow including 'retrofitting' of SuDS to brownfield areas and the development of soakaways, flood ponding areas, and so forth. 'It means a lot of lateral thinking in the study about 'soft' engineering, which is mainly done by the city, as well as the 'hard' infrastructure of the sewers, which Scottish Water will do.'

He thinks the willingness to look at these kinds of solutions demonstrates that Scotland is quite a way ahead in the UK in applying SuDS.

A joint study also gives a better chance to incorporate other factors, says Wilson. Among the most important of these are the forthcoming environmental and water quality requirements of the European Union's Water Framework Directive (WFD).

A more focused study on the water quality of the River Clyde will also be undertaken.

'That is due as part of the second phase of the study which begins shortly, ' says Fleming. 'It will look at most of Glasgow city.

'At present we have just finished the first phase looking specifically at Dalmarnock'.

That phase also included collecting general data about population, development plans and so forth.

Phase One and Two will cost about £2M overall. A third phase, due to start in the autumn and running to June next year, will expand the geographic area of the study to the whole region around Glasgow.

Feeding into the strategic study are the results from several ongoing drainage area planning studies (DAPS) for the four main areas of Glasgow.

Montgomery Watson is doing some of these as well as a separate division of Hyder itself, with the whole co-ordinated by Hyder.

'DAPS are much more formalised and rigid than the master planning, ' says Fleming, 'But the data collection and modelling can be used by us for testing options and verifying them.'

He adds that the kind of modelling which can be used has jumped in accuracy.

'Whereas a decade ago a model of Hong Kong had just four hundred nodes to create a network for the whole city, even the initial study here has 1,400.'

Flow data for the inputs into the nodes is estimated from housing and occupancy data around each input point; actual flows help verify assumptions (see box).

But model data is only part of the overview which produces a much more strategic and broad ranging assessment of the possibilities. 'So far, ' says Fleming, 'We have identified some eight 'corridors of opportunity' for combined drainage and city regeneration.'

Ongoing results from the study are fed into a joint steering group of Scottish Water and the city and that then allows the engineers there to feed their results into the planning and strategic development areas of the Glasgow City Council.

Eventually the whole process will lead to perhaps several hundred million pounds of capital expenditure, spread over 10-15 years, says Wilson. Some of this will be approved for Scottish Water spending and some from the city; there are also options for the city to insist drainage investment is included in all private sector development plans.

'Environmental features may well enhance schemes anyway, ' suggests Macnab, who says the city is determined on a 'sustainable city' image for the future.

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