ENGINEERS are preparing to create a three-mile tunnel wide enough to fit a double-decker bus under two of Scotland's most prestigious parks.

Work on what is part of the biggest upgrade to the city's waste water network in more than a century is scheduled to begin in early 2016, it has been confirmed.

The £100 million Shieldhall Tunnel, which will be more than five times as long as the Clyde Tunnel, will be created between Queen's Park and Craigton industrial estate in a route that will take it under Pollok and Bellahouston parks.

It is the jewel in the crown of Scottish Water's £250 million project to transform some of Greater Glasgow's sewerage infrastructure, a makeover of a complex system of subterranean pipes which began in early 2013.

Geoff Aitkenhead, Scottish Water's asset management director, said: "We're making good progress with this massive investment in Greater Glasgow's waste water infrastructure, the biggest in living memory.

"The environment and communities throughout Greater Glasgow will benefit hugely from this because it will protect the natural environment and meet the needs of growth, economic development and regeneration. It will also support jobs and employment opportunities, including a number of apprenticeships.

"Some major projects have already been completed and the preparatory work for others is well under way."

A separate half mile-long new sewer tunnel is to be installed beneath the streets of the Yoker area of Glasgow as part of a £7m project to help improve the water quality and natural environment of the River Clyde and tackle flooding issues.

Scottish Water has just started work on the project, which involves the construction of a new sewer tunnel more than 25ft deep from the grounds of the former Blawarthill Hospital to the north bank of the Clyde.

Contractors George Leslie, working for Scottish Water, are expected to complete the work in about a year, depending on weather conditions.

The Metropolitan Glasgow Strategic Drainage Partnership was formed as a multi-agency approach to dealing with Glasgow's aging surface water drainage system which was said to have struggled to cope with the volume of rainfall during a major storm in July 2002. Glasgow was deluged with the same amount of rain during ten hours that would be expected in a month resulting in some of the worst floods of the past 40 years.

An army of engineers are looking to complete preparatory work, including mine working consolidation and utility diversion work in advance of the start of tunnelling works.

Scottish Water believes that the work will ensure that "some of the Glasgow area's key underground assets are able to cope with its above-ground aspirations".

Dominic Flanagan, the project manager for the Shieldhall Tunnel project, added: "Being part of the Shieldhall Tunnel project is a once-in-a-lifetime work experience.

"While tunnelling projects are commonplace in large urban environments, this scale of tunnel is unlikely to be built again in Glasgow in my working lifetime."

The Shieldhall Tunnel project is described by the city council as "permitted development" which does not need special permissions and can be constructed under the Sewerage (Scotland) Act 1968.

Scottish Water say that the route has been "carefully selected to maximise the use of parkland and minimise disruption".

But there is concern in some quarters that the 15ft wide waste water tunnel, which will be the biggest in Scotland with a storage capacity equivalent to 36 Olympic-sized swimming pools, does not require an environmental assessment and does not need planning permission.

Bill Fraser, chairman of Pollokshields Community Council, who was one of the leaders of the Save Pollok Park group set up seven years ago to fight plans for a GoApe tree-top adventure attraction which never went ahead, said he was surprised.

Mr Fraser said: "I am astonished, I really am, that there is no requirement for an EIA (environmental impact assessment) because obviously if you put a great hole in the ground, there has to be some accountability.

"It's not just going under the parks, it is going under parts of Pollokshields, so I am surprised there is no environmental oversight in general."

Scottish Water says that on the advice of Glasgow City Council there is no requirement to carry out an Environmental Impact Assessment for the tunnel, being created through a commercial joint venture between among others Costain and VINCI Construction Grands Projets.

EIAs seek to ensure that the environmental effects of major projects and development proposals are fully investigated, understood and taken into account before decisions are made on whether they should proceed.

Those projects that require assessment are mainly those requiring planning permission, but also include forestry and agriculture related projects, marine works, and oil and gas pipelines.

Scottish Water say they are in close consultation with members of the Metropolitan Glasgow Strategic Drainage Partnership which includes Glasgow City Council and the Scottish Environmental Protection Agency.

The publicly owned company says most of the work will be underground and the "vast majority of people will be unaffected" by the construction phase of the project.

A SEPA spokesman added: ""We will continue to monitor the project to ensure there is no detrimental impact for areas within SEPA's environmental remit and that any activities have the required level of authorisation." 　

Publicly-owned Scottish Water started its £250m, five-year programme of work to improve river water quality and the natural environment of the River Clyde in early 2013.

Scottish Water says the improvements are required to meet European directives and Scottish Environmental Protection Agency recommendations and will contribute towards the Scottish Government's objective to comply with the European Commission's Urban Waste Water Treatment Directive and to achieve its Water Framework Directive's 'good ecological' or 'good ecological potential' status for more than 40 miles of the River Clyde and its tributaries.

Scottish Water's investment includes upgrades to about 200 Combined Sewer Overflows (CSOs) or outfall pipes - safety valves used to control waste water during heavy rainfall - on the River Clyde and tributaries such as the River Kelvin and White Cart Water at a cost of about £105m.

A total of 128 of some 222 CSOs dotted across the Greater Glasgow area have been completed.

Other key flooding projects and work to improve river water quality as part of the £250m project are under way in areas such as Cathcart, Paisley, Clydebank and Bearsden, with more in the pipeline.