Heathrow airport plans in relation to the reservoirs that supply part of London’s water
Plans drawn up by Heathrow airport, or others, to show indicative locations for new runways to the south and west show them in the areas where reservoirs are now. There are the Queen Mother reservoir; the Wraysbury; the King George VI; and the Staines reservoirs. Together they are an important water resource for London, for which water requirements grow each year as the city’s population increases. There are huge technical problems in building a runway across part of an important reservoir, the ground levels being one. With climate change likely to make future water supplies less predictable, Thames Water anticipates that there will be a slight drop, of perhaps 5%, in its water availability in 2040 compared to 2012. Meanwhile it forecast “a total increase in population in our area of between 2.0 million and 2.9 million people by 2040 – three quarters of which is forecast in London. Overall, we forecast household water demand to increase by approximately 250 Ml/d” (mega litres per day). Household water is only one sector using water. Creating a huge new reservoir to replace one removed by a Heathrow runway would be an immense undertaking. One was proposed, and rejected, near Abingdon, in 2011. Even transporting water into the Thames from the Severn would have huge costs and environmental implications.
Below is a range of articles and bits of information on the water / reservoir / Heathrow issue.
HEATHROW AIRPORT EXPANSION
THE RESERVOIR AND NATURE CONSERVATION ISSUES – by Wraysbury Parish Council
THE RESERVOIR ISSUE
The South Western Option, as published by Heathrow Airport, will destroy King George V1
Reservoir, and will impinge considerably on Wraysbury Reservoir. The document published by Heathrow Airport, entitled ‘A New Approach’, on page 26 states: ‘This option presents a more complex construction challenge due to the runway being constructed over a reservoir’.
How will this be achieved?
The banks of Wraysbury Reservoir at the southern end rise to approximately 70 feet above the surrounding land. When the reservoir is full, water reaches to approximately 5 feet below the top of the banks. It has been suggested that a ‘platform’ will be constructed to carry the runway and the two parallel taxiways over the reservoir. Such a platform would need to be at least 75 feet above the surrounding land. A 75 foot high embankment would need to be constructed across Staines Moor and through the village of Wraysbury. Such a monstrosity, if constructed, would raise manoeuvring aircraft way into the air, spreading their noise over a wide area.
If the runways were to be raised up to a height of approximately 75 feet, how would heavy aircraft climb up onto it? Aircraft are very sensitive to gradient when taxying. A large increase in engine power is required to negotiate even a small slope. Increasing engine power
significantly above idle while taxying is very undesirable and dangerous, as it greatly increases the risk of blast damage to other aircraft and adjacent ground equipment.
The use of massive winches or large lifts belongs in the realms of fantasy. Building a platform over the reservoir is therefore completely impractical.
The removal of the King George VI Reservoir is relatively simple. It would need to be drained, and the concrete, ballast and clay banks would then be used to partially fill the huge hole which would then be left. (The reservoirs go down at least 25 feet below ground level, to the London Clay strata which underly the gravel). Extra material would need to be imported to complete this infilling.
Wraysbury Reservoir would present a much more complex challenge. To construct a runway
at ground level, the reservoir would need to be drained, and the banks at the southern end
would need to be demolished.
A new bank would then need to be constructed further north, clear of the proposed runway and parallel taxiways. It would have to be carefully keyed into the existing banks to make the reservoir waterproof.
The banks of Wraysbury Reservoir are constructed with three main components. A wide puddled clay core makes the bank waterproof. This needs to be constructed with great care. It is keyed well into the impervious London Clay strata which lie about 25 feet below the surface. It would be difficult to key a new clay core into the existing one, which is about 45 years old.
The remainder of the bank is constructed of ballast, which was excavated on site. This
provides the structural stability, and supports the inner clay core.
Full document including more on conservation is at http://www.wraysburyparishcouncil.gov.uk/includes/SWOptionReservoirandEcological2.pdf
From the Mayor of London’s Draft Water Strategy, August 2009
[a few excerpts….]
“The pressure on London’s water resources is increasing. During a dry year there is an
estimated shortfall of 200 million litres a day, which is expected to increase over the longer
Climate change and an increasing population are expected to add to pressure on water supply and water resources. Although the biological and chemical quality of London’s water resources has improved, they were still (in 2004) the worst of any region in England.
The implementation of the European Union’s Water Framework Directive is likely to lead to
improvements in the water quality of London’s waterways.
A significant proportion of the capital’s water supply network dates from the Victorian era
and leakage results in a considerable amount of water being lost on a daily basis. Water
companies in London are working towards agreed leakage targets to reduce the amount
of leakage from the network, and have a duty to promote water efficiency. Thames Water
has plans to raise the level of metering in London to 77% within 15 years which could
potentially have an adverse economic effect on vulnerable groups if household water costs rise. An appropriate tariff structure could reduce these impacts.
The population of London is projected to increase by 6.6% to 2026, and to meet this growth the London Plan includes a target of 30,500 new homes per year. This population increase will also need the associated public and social infrastructure, transport, education, health-care, green spaces etc, and will place increasing demand on London’s resources, including water.
Climate change is another cross-cutting issue that will affect all aspects of life in London, and
may impact particularly on water related issues such as flooding and the reliability of supply.”
Thames Water’s website says:
“We forecast a total increase in population in our area of between 2.0 million and 2.9 million people by 2040 – three quarters of which is forecast in London. Overall, we forecast household water demand to increase by approximately 250 Ml/d.
Thames Water says:
“Every day we supply on average 2,600 million litres of drinking water to around 9 million people across London and the Thames Valley. In London most of the water we treat comes from rivers, while outside London water is mainly taken from underground aquifers via boreholes.”
“In the UK every person uses approximately 150 litres of water a day, a ﬁgure that has been growing every year by 1% since 1930. If you take into account the water that is needed to produce the food and products you consume in your day-to-day life (known as embedded water) you actually consume 3400 litres per day.
“This is quite alarming if you consider that the UK has less available water per person than most other European countries. If you live in the South east of England it is even more so, as this part of the country is the most water stressed.”
From Thames Water’s Revised Draft Water Resources Management Plan 2015 – 2040
with more detail at https://www.thameswater.co.uk/about-us/5392.htm
This shows they predict less water to be available over this period. The population will be larger, and the water companies depend on less water being used per person.
This shows the runways near Heathrow, as they are at present:
The Wraysbury Reservoir is a water supply reservoir for London lying just west of the M25 near the village of Wraysbury and Heathrow airport. The reservoir was begun in 1967 and completed in 1970 with a capacity of 34,000 million litres.
The reservoir is owned and operated by Thames Water and 400 million litres of water are pumped daily from an inlet at Datchet on the River Thames. A neighbouring reservoir is the King George VI Reservoir, opened in 1947, which is supplied from Hythe End. To keep grass on the reservoir short and make inspections easier, Thames Water maintains a flock of sheep on the earthen banks.
Wraysbury Reservoir is within a Site of Special Scientific Interest which also includes gravel pits at Wraysbury.
The King George VI Reservoir lies to the south of Stanwell Moor near Stanwell and Heathrow. The reservoir was opened in November 1947 and named after the then reigning monarch King George VI. It is owned by Thames Water.
The reservoir occupies 350 acres (1.4 km2) and holds 3,493 million imperial gallons [15.8 million litres] (15,880,000 m³). Its maximum height above the original ground level is 56 ft (17 m). Like the other Lower Thames reservoirs, it is of traditional earthen dam construction, with a puddled clay core supported by ballast embankments built from materials excavated on site. It is entirely man-made, as the area had no natural topographical features that could be dammed off to create a reservoir. To make inspecting the integrity of the reservoir easier, Thames Water maintains a commercial flock of sheep on the reservoir banks to keep the grass on the reservoir banks close-cropped.
The reservoir was completed in 1939 but was left empty due to the outbreak of the Second World War. It was reputed that a mock Clapham Junction railway station was built inside to confuse the Luftwaffe. The reservoir was used for fog dispersal experiments in the development of the FIDO landing system.
This reservoir and the adjacent Staines Reservoirs receive their input from the River Thames at Hythe End just above Bell Weir Lock. The Staines Aqueduct continues eastwards, passing the Water Treatment Works at Kempton Park, to supply the Water Treatment Works at Hampton. The other adjacent reservoir, Wraysbury Reservoir, is situated to the west on the other side of the M25.
The reservoir forms part of the Staines Moor Site of Special Scientific Interest. The reservoirs carry nationally important wintering populations of tufted ducks, pochard, goosander and goldeneye.
The Staines Reservoirs lie to the east of the King George VI Reservoir near Heathrow airport in the county of Surrey within the Colne Valley regional park. The village of Stanwell is nearby as is the town of Staines. The two reservoirs are placed between the A3044 and the A30. They were built in 1901.
The area has been designated a Site of Special Scientific Interest (SSSI) as it carries important wintering populations of tufted ducks, pochard, goosander and goldeneye.
The Queen Mother Reservoir lies between the M4 and the M25 to the west of London. It is 475 acres (1.922 km2) in size or about 1 km in diameter – making it one of the largest inland areas of water in Southern England. It is managed by Thames Water.
This is one of a number of reservoirs to the west of London and was built in 1976. Its water is pumped from the River Thames nearby. The water improves in quality during its retention in the reservoir as solids settle and organic contaminants are adsorbed, absorbed and degraded through a combination of natural biological processes aided by sunlight and oxygenation. Water from the reservoir is treated (often using slow sand filters) before being put into supply as London tap water.
The reservoir lies within the Colne Valley regional park and like other local reservoirs is popular for sailing and bird-watching. Petrels have been spotted at this reservoir.
Supplementary Written Evidence from Foster + Partners (AS 39A) on Aviation Strategy, to the Transport Select Committee
given to Parliament on 7.3.2013
(Foster supporting its plan for an airport in the Thames estuary, and opposing growth at Heathrow).
Comments on Policy Exchange four runway proposal for Heathrow
The proposal would require the closure of the Wraysbury reservoir and we have assessed the main impacts on the water supply system, environment and the road network.
Water supply system
The reservoir stores 34,000 million litres of water and 400 million litres of water are pumped daily into the reservoir from River Thames at an inlet at Datchet. The reservoir is part of the Thames Valley stored water system of a network of 12 reservoirs serving London.
The reservoirs are pumped storage schemes dependent on raw water from the River Thames.
The closure of Wraysbury would have serious implications for household and businesses in London particularly in a dry year, such as the [early] 2012 drought where water restrictions were introduced. Without Wraysbury, more severe water use restrictions could have resulted from the drought with significant costs to businesses in addition to costs to households.
Finding a replacement reservoir with a suitable source of water would take a minimum of 10 years from concept to completion under current planning regulations. Presumably the costs of this would also have to be covered by the airport.
Wraysbury Reservoir is a Site of Special Scientific Interest (SSSI) in its own right. It is also part of the South West London Waterbodies Special Protection Area and a Ramsar site. As such, the normal environmental regulations apply for a European site. These include the need to comply with the Habitats Regulations, the need for an assessment /Appropriate Assessment and the need to prove imperative reasons of overriding public interest (IROPI) for closing the reservoir and to ensure provisions for compensation.
It is worth noting that an expanded Heathrow would significantly increase the numbers of flights over the centre of London, and the number of people in the Capital suffering unacceptable levels of noise.
4 March 2011 (BBC)
Abingdon £1bn reservoir plan rejected by government
Plans for a £1bn reservoir in Oxfordshire to supply more than eight million people over the next 25 years have been rejected by the government.
Thames Water wants to build a site on four square miles of land near Abingdon to help ensure future demand is met.
The bid went to a public inquiry but the secretary of state said there was “no immediate need” for such a site.
Thames Water said it would look at developing plans for a smaller reservoir at Abingdon.
In a statement the Department of Environment, Food and Rural Affairs (Defra) said: “The secretary of state [Caroline Spelman] has accepted all of the recommendations included in the planning inspector’s report.
“The report included a number of complex recommendations that require a significant amount of further work on the part of Thames Water.”
Defra said Thames Water had been told to scrap the current plan and consider a proposal for a smaller reservoir.
The water company said the reservoir, which would have held 100 million tonnes of water, was necessary to meet future demand for water in the South East but that it was willing to alter its plans.
Martin Baggs, Thames Water’s chief executive, said: “The [planning] inspector has specifically asked us to develop a proposal for a smaller reservoir at Abingdon, which will be one of a number of options available to us.”
Campaigners had fought the plan, claiming there was no need for such a large reservoir and that it would damage the environment.
Leader of the Vale of White Horse Council Tony de Vere said: “We are delighted with this decision.
“Local residents were very worried about the impact of such a large reservoir and we share their relief that the plan has been axed.”
Related BBC Stories
17 August 2010 (BBC)
Abingdon reservoir inquiry draws to close
A public inquiry into plans for a massive reservoir in Oxfordshire is due to come to an end this week.
Thames Water is proposing the development, which would cover four square miles of land south west of Abingdon and cost £1bn.
The water company says the reservoir is necessary to meet future demand for water in the South East. It will finish making its case on Wednesday.
Campaigners say it is not needed and would damage the environment.
The Cotswold Canal Trust, the Group Against Reservoir Development (GARD) and the Environment Agency have all submitted their closing statements this week.
The inquiry began in June at the Oxford Conference Centre in Park End Street. The result is expected later this yea
15 June 2010 (BBC)
Inquiry into £1bn Oxfordshire reservoir plan
A public inquiry has begun in Oxford into plans to build a £1bn reservoir.
Thames Water (TW) wants to build the facility, which would hold 100 million tonnes of water, on land near Abingdon.
A spokesman said water supplies in the area were already stretched and the reservoir would help ensure demand is met over the next 25 years.
Campaigners the Group Against Reservoir Development (GARD) claim the plan is not a “cost effective and environmentally sustainable” option.
In a statement, it said: “GARD’s objective is to persuade the Government inspector chairing the inquiry to conclude that TW’s Abingdon reservoir is not needed.”
The Wantage & Didcot MP Ed Vaizey has campaigned for a public inquiry, which he hopes will allow all the arguments to be heard.
He added: “I have always maintained that Thames Water must be held to account and its plans scrutinised.
“There are perfectly viable alternatives to a reservoir, as well as clear ways to reduce water consumption so that a reservoir is not necessary.”
TW identified the South Oxfordshire site more than five years ago and the inquiry follows a public consultation in 2007.
Martin Baggs, of TW, said the company supplies water to 8.5 million people.
“We take this responsibility extremely seriously. After consulting widely, our customers have told us they do not want us to take any risks with the security of their water supply,” he added.
Need for reservoir ‘not proven’
|The Environment Agency has said it is not convinced there is a need to build a £1bn reservoir in Oxfordshire.The controversial development near Abingdon is designed to safeguard London, Oxfordshire and Swindon’s water supplies in case of a drought.But the plans would also mean that some residents could be forced to move.A series of public exhibitions showing detailed plans for the reservoir – the biggest to be built in the UK in 25 years – starts in Abingdon on Saturday.The exhibitions will focus on what the reservoir may look like, how it would work, the impact of construction on the local communities and local wildlife and recreation.A consultation began in September last year but the Environment Agency said Thames Water has failed to respond fully to some central issues and had not proved a need for the reservoir.Craig Woolhouse, area manager for the agency, said they agreed that Thames Water could not meet the forecast growth in water demand without finding a new water source.But he added: “We still believe the company can take its leakage reduction and demand management much further to reduce impacts on the environment from use of water.”
Water watchdog Ofwat has described Thames Water as the UK’s leakiest supplier.
The company said it would continue its discussions with the Environment Agency and the county and district councils, to address issues raised.
The reservoir would be half the size of Windermere in Cumbria and hold 150 billion litres of water pumped from the River Thames.
If the plan is approved, the reservoir could be built within 15 years.
Richard Aylard, Thames Water’s environmental director, said they are inviting local people to have their say on the plans.
He said: “We are aiming to help people understand the scale and technical requirements of the reservoir, including what construction will be necessary and where pipelines and treatment works might be sited.
“We want this to be a real opportunity for local people to help shape their environment.”
STATEMENT BY GARD
4th March 2011
RESERVOIR REJECTED – PLAN MUST BE RE-EVALUATED
The Secretary of State for DEFRA has now published the report by Inspector Wendy Burden on the Thames Water (TW) Water Resources Plan following the Public Inquiry last year.
She has accepted the Inspector’s conclusions which were that the plan did not meet the statutory requirements under the Water Industry Act, and that the measures Thames Water proposed should be adopted were not fully justified by the evidence.
The Inspector concluded that changes to the plan were needed including:
• Deletion of TW’s premise of ‘long term risk’ associated with future, unknown, sustainability reductions.
• Deletion of all programmes with the objective of meeting that long term risk.
• Inclusion of a wider range of feasible options.
• Changes to be made to the methodology for programme appraisal to bring it in line with good industry practice, with a clear description of the process set out in the plan.
• Use of a sensitivity analysis to cover the potential for future sustainability reductions and identifying a choice of options from the feasible options list to meet the different levels of sustainability reductions.
The Inspector also believed that the minimum necessary, should the Secretary of State take a pragmatic approach, would be for Thames Water to demonstrate a security of supply, and to revise its programme appraisal to identify a new preferred programme for the London and South west Oxfordshire water resource zones.
GARD concludes from this that the reservoir proposal is therefore ruled out for the immediate future.
GARD has played a major part in opposing Thames Water’s flawed plan to build a massive reservoir on 5,000 acres of productive farmland South West of Abingdon.
The proposal would cost £1billion, take about 10 years to construct and result in considerable additional charges to consumers.
At the Public Inquiry last summer GARD was represented by an outstanding QC, Nathalie Lieven, using the evidence of two nationally acknowledged expert water resources witnesses, Chris Binnie and John Lawson. Their evidence clearly demonstrated that the need for the reservoir had not been proved, and that if the need for a large additional water resource arose in future there were cheaper, quicker and less environmentally damaging alternatives to the reservoir which the company had not properly considered.
In addition to GARD’s evidence, the CPRE (Campaign to Protect Rural England), Oxfordshire County Council, the Vale of the White Horse District Council, and significantly, the Environment Agency presented well prepared cases against the plan.
The Secretary of State’s ruling means that Thames Water must now investigate fully and objectively several alternative long term water resource proposals, including Severn-Thames transfer, which they failed to consider properly in the preparation of their 2,000 page plan, because, it must be assumed, Thames Water’s owners regarded their water customers’ interests were secondary to those of their shareholders.
GARD is most grateful for the support given by our local MPs, Ed Vaizey and Nicola Blackwood, other elected representatives including Iain Brown, and of course our members.
Information from GARD (Group Against Reservoir Development)
THAMES WATER’S DRAFT PLAN FOR 2015-2040
BACKGROUND: Following the public inquiry held in 2010 into Thames Water’s 2009 Plan, the inspector found that the TW’s proposals were not fit for purpose, not compliant (over estimated demand) and that some important alternatives to the proposed Abingdon reservoir (Upper Thames Reservoir UTR) south west of Abingdon had not been properly investigated, particularly the options involving water transfers from R Severn to R Thames to supply London’s reservoirs. The inspector ruled out TW’s proposed 100 million cubic meter reservoir. Consequently, TW’s plan was subsequently amended as a result of these findings.
NEW PLAN: In March 2013 TW posted their next draft Water Resources Management Plan (dWRMP 14) covering the 25 year period to 2040, on their website. It called for public consultation by 23 July 2013. It is not for GARD to detail TW’s plan here but, in general terms, TW is forecasting an increasing deficit in the available water supply resulting from their forecast population growth and climate change trends over the 25 year period ahead.
TW plans to address this deficit by reducing per capita consumption through public education and compulsory metering to 142 litres per head per day (from the current level of about 160 litres per head per day). TW also intend to continue their leakage reduction programme, but on a very surprisingly unambitious scale and then only, until 2020. Thereafter, TW maintain leakage at a constant level rather than reducing it to the considerably lower UK water industry average which TW themselves said was achievable in their previous plan.
It is GARD’s view that the actual deficit will be considerably smaller than TW’s plan states, and that their leakage reduction proposals should not only be much more ambitious but should extend well beyond 2020.
On the water supply side, TW’s plan envisages a large increase in re-use of treated effluent as a sustainable method of increasing supply, but their method proposed is based on an energy intensive process known as reverse osmosis (RO). Although RO is 100% safe, TW believe there is a risk that public consultation will reveal aesthetic objections to recycled treated water usage, a concern that would also apply to more conventional, alternative treatment/purification processes.
To ensure adequate supply beyond 2030, TW’s dWRMP 14 plan intends to bring in a major new resource from one or more of the following three options, each of which requires considerable further research work:
- A new UTR reservoir near Abingdon of, as yet, unspecified capacity.
- Further development of water re-use based on improved treatment methods.
- R Severn to R Thames bulk water transfers to top up TW’s London reservoirs, as required.
To achieve cost effective, long term and sustainable solutions, the challenge still faced by Thames Water is to carry out essential environmental, technical and economic research work on each of these three main options over the five years leading up to their next 5 year plan from 2019.
GARD is convinced that bulk transfers from River Severn into River Thames will prove to be the most appropriate, least costly and least environmentally damaging solution. In contrast to other alternatives, it offers very significant scope for future increases and development of water supplies for London, particularly when additional resources are offered from United Utilities’ Vyrnwy Reservoir are included. Crucially, this would eliminate any dependency on the R Thames flows or on ground water supply sources.
There are various publications from GARD at http://www.abingdonreservoir.org.uk/downloads.html
Mr John Lawson MA, FREng, FICE, FCIWEM
Key technical advisor to GARD
John Lawson is a civil engineer specialising in water resources engineering with a degree in mechanical sciences from Cambridge University. Fellow of the Institution of Civil Engineers (ICE) since 1985 and of the Chartered Institution of Water and Environmental Management (CIWEM) since 1988, he was invited in 2002 to become a Fellow of the Royal Academy of Engineers in recognition of his contribution to water resources engineering.
He served on the Water Resources Expert Panel of CIWEM from 1994 to 2002 and was its Chairman from 1997 to 2002. He served on the Water Board of the Institution of Civil Engineers from 2002 to 2007, and was its Chairman from 2003 to 2007.
He worked for Halcrow Group Ltd., Consulting Engineers, from 1968 to 2007. Throughout his career he was engaged on projects for water supplies, flood control, irrigation and hydropower, becoming a Director of Halcrow Group Ltd. from 1990, and Managing Director of its water business from 2003 to 2007. He has been responsible for numerous water resource planning studies in England and Wales, with a particular focus on minimising the impact of abstractions on the environment.
From 1991 to 1994 he was responsible for Halcrow’s work assisting the National Rivers Authority to develop its water resource strategy for England and Wales, which was published in 1994. This involved helping the NRA and water companies to examine a wide range of strategic options to meet future demands, including the Severn transfer and the Abingdon reservoir. His role in this was project manager, coordinating the work of the NRA and all the water companies concerned, including assisting the NRA in analysing the strategic options and developing their strategy.
Since his retirement from Halcrow he has worked as a voluntary water resources adviser to Action for the River Kennet, and the Wye & Usk Foundation. He is also a Trustee of the Thames Restoration Trust. In 2007 he prepared a report for Halcrow on transferring water to the Thames catchment from Wales, including the Severn transfer.
Plans for new reservoirs
The reservoir plan for Abingdon
New houses being built in the South East mean water demand is rising. Seven new reservoirs could be built across the South East to cope with the rise in demand for water.
A joint investigation by BBC’s Countryfile programme and the Independent on Sunday discovered that water companies are planning to flood thousands of acres of farmland.
Among the places earmarked for new reservoirs are Canterbury, in Kent, and Abingdon in Oxfordshire, where plans which had been discarded years ago have now been revived.
Thames Water first presented plans for a reservoir in Abingdon in 1990 but they were withdrawn after being told they had to deal with leakage from water mains first.
Possible water restriction
Now it has been revealed the water company has revived the scheme and has included the proposal in its business plan.
If built, the reservoir would cover half of farmer Neil Walker’s fields and buildings.
He said: “We could literally end up under 40 feet of water.”
But water companies say new reservoirs are needed because of all the new homes being built and the increased amount of water being used with dishwashers and power showers.
Dr Peter Spillet, from Thames Water, said: “When you look ahead 20 to 25 years we can see a big gap developing between supply and demand and we have used the more conventional more economical, least cost approaches we can think of.
The site of the planned reservoir in Kent
Mid Kent Water already owns some land earmarked for the reservoir
“A large, regulating reservoir up stream would be a good solution.”
The seven reservoirs would only be built if permission was granted from the government and the Environment Agency.
But Baroness Young, Environment Agency chief executive, said: “The point we are making in being pretty resistant to reservoirs is that most companies that put forward proposals for reservoirs are not thinking about how they can reduce customers’ demand and manage their leakage effectively as a first step.”
She also said if there was a dry winter there may be restrictions on water usage in the spring and summer next year.
In Kent, plans have been revived for a mile-and-a-half long reservoir in Broad Oak. The proposals were first drawn up in 1974.
Mid Kent Water has said it is needed because of the thousands of new homes planned for the county.
Policy Exchange map of their plans for Heathrow …..
Compared to the existing situation (and proposed location of a 3rd runway). The existing runways are about a mile apart. The Policy Exchange seems to be putting the runways in each pair very close together.
Heathrow unveils a new approach to third runway
17 July, 2013 (Heathrow Airport press release)
Illustrative map indicating location of south western runway, over current reservoirs.
- 2 other runway plans from Heathrow at http://news.sky.com/story/1116793/heathrow-options-for-third-runway-revealed