Thames Tideway Tunnel Mythbuster

As experts, academics and the EU Environment Commissioner say, it’s time we learnt to work with nature, rather than against it.

Thames Water appear to have convinced many politicians and the public alike that London is just about the only place in the world where sustainable Green Infrastructure (GI) would not be an effective mitigation for the issue of rainwater flooding combined sewers, causing overflows.

Below we demonstrate that ten of their favourite myths don’t stand much scrutiny…

(click on each heading to read the corresponding mythbuster or use: expand all / collapse all)

Myth 1: The Thames Tideway Tunnel (TTT) would be a “supersewer”
  1. The primary cause of overflows in London’s original (“Bazalgette’s”) sewer system is that it gets flooded by rainwater.  This is because by design, it combines sewage and stormwater in the same pipe.  Portions of the system are prone to run out of capacity when it rains too much.
  2. Hence, the primary issue is rainwater, which is actually a valuable natural resource.  Preventing or delaying it from entering the sewer system is the best way to prevent overflows.  This is what Green Infrastructure (GI) aims to achieve – among many other benefits.
  3. The TTT (or “super-sewer”) would actually carry a combination of rainwater and sewage.  As such, calling it a “sewer” is rather misleading[1]
  4. The “combined sewer” design is now widely recognised as flawed and no longer implemented[2].  However the TTT would essentially perpetuate this outdated practice of combining sewage with rainwater, postponing proper resolution of the issue.


Myth 2: Green Infrastructure (GI) is too costly / the TTT is far cheaper

  1. This is as a bold claim, considering the TTT’s estimated capital cost has already gone up over three times its original estimate [3], even before the first drop of concrete has been poured under the river it’s supposed to protect.
  2. The tunnel is so costly that it cannot be covered by the normal “sinking fund” consumers pay into through their water bills, for infrastructure to be maintained and upgraded [4].
  3. Further the Government chose to step in to commit uncapped taxpayer-backed “contingent financial support” as the TTT couldn’t be financed by Thames Water alone.  How can anything be more expensive?   And TW’s shareholders cannot be expected to contribute to the expense or share the associated risk, despite the billions they’ve cashed in in dividends and other opaque financial transactions over the years…?
  4. When Thames Water compared GI with their tunnel, they included all operation and maintenance (O&M) costs on the GI side but not on the tunnel’s – is this a fair comparison[5]?
  5. With help from engineers, we have costed one GI solution consisting of porous asphalt[6].  Its capital cost (comparing apples to apples) is about £3.2bn, which is at least £1bn (or roughly 25%) cheaper than the tunnel’s latest estimate[7].
  6. Financing – the cost of which is not included in the capital cost comparison – is bound to be significantly cheaper for GI because it’s piecemeal rather than “big bang”.  Further, EU financing assistance for GI is to become available as early as 2014[8].  Martin Blaiklock, a noted specialist in infrastructure finance estimates that financing for the TTT will be of the order of £5-6bn – bringing the total bill to £10bn.  No surprise TW don’t advertise this figure…
  7. Because it is far less risky in financial and technical terms, GI would not require an uncapped taxpayer guarantee to a private company, which the Treasury famously describes as “impossible to monetise” (paragraph 21 of this explanatory note to the Water Industry (Financial Assistance) Act 2012)[9].
  8. It’s true that the tunnel’s cost could be directly shared among more people, TW’s 14m sewerage consumers, reaching as far West as Cheltenham for example.  For an obscure reason, the hike would spare TW’s commercial customers.  We think it would be fairer for everyone in London to pay for remediation of the city’s drainage issues, including those commercial consumers[10].
  9. TW’s CEO, Martin Baggs, admitted at a panel discussion[11] that “without SuDS[12], the TTT has a very short lifespan”.  In other words, some unaccounted and unknown SuDS costs will have to be added to the tunnel’s in any case for it to be effective.
  10. Finally, privatised Thames Water, like any corporation, has one overriding aim: maximise profits for its shareholders. Their interest may not always be best aligned with those of the public. A ‘tip of iceberg’ illustration of this surfaced when, in October 2013, an Ofwat inquest revealed that TW had overstated the cost of land acquisition for the TTT, attempting to pass that on to their consumers by charging them an extra £29[13].


Myth 3: GI would take too long to become effective

  1. Another reason we chose porous asphalt as a reference GI solution is that it dispels this myth: in the 10+ years it would take to get the TTT operational, roughly 50% of London’s primary roads and a third of secondary roads will be resurfaced[14].  This would be nearly enough to address the issue by itself, with little extra effort or disruption[15].
  2. Unlike the tunnel, GI will start cleaning up the river immediately and incrementally, whereas one would have to wait until 2023 (assuming no further delays[16]) for the tunnel to become operational.
  3. Within 2 years, our proposed short term workaround could help mitigate any concerns with the pace of GI implementation[17].
  4. Had we started with GI earlier, much progress would have been achieved by now[18].  While hindsight won’t be of much help, we should take heed now and stop postponing the implementation of GI, when even TW admit it is a necessity!


Myth 4: Implementing GI would be extremely disruptive

  1. Implementing the porous asphalt solution would incur very little additional disruption, since roads are being resurfaced anyway (see 3.1 above).  Green roofs happen… well, on roofs, which are currently underused; so again, no significant disruption.
  2. Disruption for additional implementation of, say stormwater tree trenches or rain gardens, would have minimal and scattered impact, as opposed to the tunnel which imposes a substantial penalty on some “unlucky few”, who would see their lives heavily impacted[19].


Myth 5: There is no space for GI in a dense city like London

  1. Publicly available data indicates that for inner London (the combined sewer catchment area), 38.1% is gardens, green spaces and open water and 21.5% is roads and paths and 26.5% buildings.  The good news is that all three categories are suitable for GI…
  2. The porous asphalt solution by itself dispels this myth easily: less than half of London’s roads would need to be converted – even less when combined with other GI techniques.
  3. Another figure that TW bandy around, in the hope to make people think it’s simply impossible to implement GI in the required scale, is that it would take a surface equivalent to 40x Hyde Park for it to make a difference and “where do you find that space”?  This actually compares neatly to the 100x Hyde Park of paved over front garden space[20] that could/should be converted to permeable paving or porous asphalt[21].
  4. A 2008 survey by the Greater London Authority assessed that there are 10 million square meters of roofs suitable for greening within a 6Km radius of Trafalgar Square[22].  Green roofs, like most of the GI toolkit, come with substantial ancillary benefits.
  5. So all that needs to happen is that a subset of the above be converted using suitable GI techniques.  As previously discussed, this needn’t be overly disruptive.  Regardless of the specific issue of sewer overflows, which would be solved as just one of the benefits, this GI adoption is necessary if London is to be turned into a sustainable city ready to face 21st century environmental challenges[23].


Myth 6: London’s geology is not adequate for GI

  1. Unlike what TW would have everyone believe, close to half of the geology of the catchment consists of sand gravels, which are eminently suitable for infiltration.
  2. TW further claim that those sand gravels are “permanently saturated” and therefore unsuitable for infiltration.  Those with slightly longer memories will remember that only a year ago, London experienced a protracted drought, a key cause of which was that aquifers were severely depleted.  London is classed by the Environment Agency as “seriously water-stressed”[24].
  3. Somehow, London’s geology is capable of accommodating the 650 mega-litre of fresh water that TW squander every day from their leaking pipes.  This is six times the volumes of sewer overflows, which clearly compounds the drainage issues[25]!  TW claim this is “too hard and too expensive” to fix but somehow, equally old and complex Paris manages a leakage rate of 9% compared to TW’s 28%[26]


Myth 7: Bazalgette’s original sewer system can no longer cope with London’s expanding population

  1. Bazalgette famously had the foresight to design his system for twice the worst case capacity scenario he had calculated at the time, factoring in significant overcapacity.
  2. One of TW’s favourite misleading myths is that London’s population has increased from 2m in Bazalgette’s days to 8m today.  It’s therefore meant to be obvious that his sewer system has to be overwhelmed.  What they omit to say is that most of this population growth occurred away from Inner London (served by Bazalgette’s original combined sewer system)[27].  In fact, the population in Bazalgette’s catchment is well within the limit for which it was designed.
  3. If London is facing sewer capacity issues, it seems likely this could be due to TW’s negligence in the maintenance of their sewer network[28]. This point was recently underscored by Sir Ian Byatt, eg Director General of Ofwat in his paper: “Thames Tunnel; A Critique of a Flawed Project“. He notes that there were no sewer capacity issues in Central London when he left Ofwat in 2000 and that the nominal population increase since then cannot explain the alleged capacity issues[29].


Myth 8: Only the Thames Tideway Tunnel can achieve clean waters

  1. Despite its exorbitant cost, the tunnel is designed to still allow each connected CSOs to overflow four times a year each, at commissioning[30].  This will worsen due to escalating climate change, to which the tunnel contributes with its own substantial carbon footprint.  Climate change increases risks of extreme weather events, to which the tunnel, with its finite capacity, is not resilient[31].  This is illustrated in our “Thames Tunnel and Climate Change Vicious Cycle” infographic.
  2. Grey infrastructure is notoriously subject to “incidents”, of which a sad, long list exists.  This Guardian article tells just one such story, which saw TW annihilate all life in the River Crane.  What would happen when a “sluice gate gets stuck” in TW’s massive single pipe concentrating so much of London’s sewage and rainwater?
  3. The TTT documentation makes mention of “allowing very infrequent residual spills to the River Lee at Abbey Mills to protect the tunnel system from high water levels during extreme rainfall events”28.  Here’s an example to help the reader understand what this might mean: Mogden Sewage Treatment Works, which recently underwent a £140m (our cost) upgrade has similar wording in its specification.  In the same month of May 2013 that upgrade was inaugurated, the plant released over 81,000 m3 of activated raw sewage into the Thames in just a few hours.  Such is the dependability of grey infrastructure.  Concentrating so much of London’s sewage and rainwater down a single pipe would make it a prime risk for such “incidents”.
  4. The tunnel will have to undergo major maintenance (several weeks’ duration) at least once every ten years, during which time it will presumably not be operational.  What will happen with the sewage/rainwater during that time?
  5. The tunnel will have to be relined well before its design life (100 to 125 years according to TW) is elapsed.  This will be a lengthy operation; again, what will happen?
  6. The picture is the exact opposite with GI; by its distributed nature, it is resilient and can be complemented or improved at any time, if found deficient or where additional capacity is required.


Myth 9: London’s environment and economy need the TTT

  1. Because it fails to consider the integrated water cycle, the TTT would only improve one aspect of the environment (water quality) at the expense of almost all others, such as but not limited to:
    • Climate change, owing to its substantial carbon footprint
    • Water security, because it doesn’t help mitigate drought
    • Natural defences, because it doesn’t help to restore natural drainage
    • Air quality, due to increased pollution both during construction and operation.

    GI (as the concept implies) does the exact opposite and much more; for example, green roofs reduce a building’s energy consumption, which in terms mitigates climate change.

  2. Of the (peak) of 4,000 people due to be employed directly during construction of the tunnel, TW have made the ambitious pledge to “meet a target on employing in excess of 20% local labour”[32].  This is because, firstly tunnelling requires specialized skills which are more easily sourced abroad and secondly TW’s contractors will want to maximize their profit margin.  So this is a peak of 800 local jobs we’re talking about here, which will revert to a few dozen once construction is complete.  Contrast this with GI, which will create a lasting, local, green collar industry.  In NYC, the Department of Environment Protection is pledging to create up to 3,000 such green collar jobs every year[33].


Myth 10: “GI would simply not work”

By now, you will have seen a pattern.  Every single one of TW’s excuses to dismiss the sensible 21st century Green Infrastructure solution has clouded, muddled, obscured or displaced the truth in some way or other, so as to make it appear their darling tunnel proposal is the only solution.

  1. Whilst it’s true that widespread application of GI to solve stormwater management issues is relatively new[34], it’s already proving so successful in the US and Germany to name but two examples, that both the US Environment Protection Agency and the European Commission’s DG Environment have publicized policies that Green Infrastructure and integrated water management[35], should be the preferred approach to deal with CSO discharges.  Binding legislation to this extent will doubtless be passed soon.  In other words, the TTT would likely be outlawed within a few years[36]
  2. One of GI’s big advantages is to be able to assess and correct deficiencies incrementally as needed, with each additional GI measure bringing its own ancillary benefits.  With a “one size fits all” solution that is the TTT, if there’s a problem[37], it could turn into a massive sunk cost[38].

(expand all / collapse all)


Considering the sheer number of red flags listed above, the lack of due diligence in the TTT’s examination process and willingness of some politicians to accept TW’s word as gospel is a real concern.

Only you, dear reader, can make a difference by signing the petition to ensure that, at the very least, the above aspects are thoroughly investigated before our generation’s biggest spend on an environmental project can be committed.

(version 1.2, published 12-Sep-2013, updated Feb 2014)

  1. [1] By accepted estimates, 80% of the TTT’s content would be rainwater; it is therefore more accurate to describe it as a “super rain drain” than a “super sewer”.
  2. [2] This was actually already recognised as such in Balzalgette’s days.  The only reason combined rather than separate drains were laid was to save costs.  Ever since then and as London expanded, separate systems were laid as can be seen on historical drainage maps.
  3. [3] According to Consumer Council for Water: “The total costs of the complete Tideway schemes have increased from £1.7bn six years ago to £4.6bn today” (Jan 2011). Less than a year after this writing, a further £500m was added to the estimate. So the cost has escalated from £1.7bn to £5.1bn (2011 prices).
  4. [4] However, by many accounts, Thames Water could have paid for much of their tunnel themselves if they had been a little less profligate, distributing billions in dividends and other payments to its shareholders.  See for example “Water companies told to stop siphoning off cash to foreign owners”, the Independent, 17 July 2013
  5. [5] Source: Appendix D of TW’s ‘needs’ report for the TTT.  Actually the fact that the tunnel’s O&M as well as financing costs are not clearly disclosed is a major concern in and of itself.  The only thing we know for sure is that the bill increase, which TW’s 14m residential customers would be subjected to, would be permanent so one can infer these costs would likely dwarf the corresponding costs for GI.
  6. [6] Porous asphalt isn’t the only GI solution or some sort of preferred measure to be taken in isolation.  Green roofs and most GI measures are also less costly.  We use this as a reference since it has been easy to analyse government data, obtain cost and assess it in terms of feasibility as we discuss further.
  7. [7] The tunnel’s last known capital cost estimate is £4.1bn in 2011 prices or £4.2bn in 2012 prices…
  8. [8] No such assistance will be made available for unsustainable tunnels, for obvious reasons.
  9. [9] Bearing in mind TW is mainly owned by overseas financial institutions used to collect a 20% levy on every penny paid by 14m captive consumers, this may not be the smartest move.
  10. [10] The cost can be shared even more fairly by incentivising households and companies to contribute less stormwater to sewers by installing GI on their premises, bearing in mind stormwater is the primary issue we’re dealing with here.
  11. [11] At the Institution of Civil Engineers on 20th May 2013.
  12. [12] SUDS = Sustainable urban Drainage Systems, this means roughly the same as Green Infrastructure.
  13. [13] page 23 of this Ofwat report
  14. [14] Road resurfacing data from the Asphalt Industry Alliance ALARM survey.
  15. [15] Other, perhaps, than designing it to maximize infiltration rather than temporary retention.
  16. [16] If history’s any guide… the Channel Tunnel, to which TW like to compare their engineering feat, ended up taking 20% longer to complete than planned, and also incurred 80% cost overruns, with financing costs being 140% higher than original forecasts…
  17. [17] A number of innovative, sustainable and complementary approaches such as the Japanese ‘Hydrospin’ screen, which has already been installed over 1,000 times, have not been adequately considered by TW and have great potential to significantly reduce pollution in overflows in a very short time frame.
  18. [18] Some enlightened cities, such as Stuttgart in Germany or Zurich, Switzerland, started heavily investing into GI (particularly green roofs) as early as the 1980’s.  As a consequence, they enjoy today much better water quality levels than the tunnel would ever be able to deliver (the tunnel would still allow sewer overflows 4 times a year, initially…).
  19. [19] In some cases for up to seven years; including several years of 24/7 industrial site work in the midst of dense residential neighbourhoods in the direct vicinity of schools and sheltered homes.
  20. [20] UK-wide figure but it’s not too far-fetched to think that 40% of these are in London.
  21. [21] Local Authorities have powers to ensure this but don’t use them.  Possibly the biggest part of the work that’s necessary to arrive at a sustainable London is to rationalize the regulatory framework.  Lobbying finds an easy target in some work-shy politicians who claim this simply cannot be done (again!).  Other cities, such as Philadelphia, New York, Dublin or Hamburg, which have the courage of looking at their sustainability challenges in the eye show it can be done.  If our politicians aren’t up for the task, they need to be replaced.
  22. [22] It’s true that deploying GI will required some creativity, as opposed to “same old” unsustainable practices of mixing precious rainwater with sewage in countless tonnes of concrete.  The creativity of GI is exemplified by the recently unveiled Living Wall on Victoria’s Rubens at the Palace Hotel.  Fighting climate change will require some serious thinking outside the box and this is a prime example of both the opportunity and the challenge.
  23. [23] In the aftermath of 2012’s Hurricane Sandy, New York City, which already possessed a robust Green Infrastructure plan recognised the need to boost it much further to better weather the next storm (see NYS 2100 commission report, Cross Cutting Recommendations, p.12).  London, as we know too well, is also prone to flooding…
  24. [24] In the aftermath of 2012’s Hurricane Sandy, New York City, which already possessed a robust Green Infrastructure plan recognised the need to boost it much further to better weather the next storm (see NYS 2100 commission report, Cross Cutting Recommendations, p.12).  London, as we know too well, is also prone to flooding…
  25. [25] All this (clean) water is either infiltrated or runs down combined sewers (an industry estimate is that this might be the case for 40% of this volume), severely compounding the sewer overflow issue.
  26. [26] TW have no incentive to fix the leaks because we pay for the leaked water as well.
  27. [27] This fascinating animated graph shows how the geographical distribution population of London evolved.  Bazalgette’s system was designed for 2x2m, which today’s central London population is well within (offices and commercial premises rather than overpopulated Dickensian slums).  Outer London is thankfully served by a separate system which doesn’t combine rainwater and sewage, unlike the outdated and flawed practice that the TTT would perpetuate.
  28. [28] An example of this can be found in this recent report of a sewer blockage in West London, of 15 tonnes of waste, which was only discovered when residents complained they couldn’t flush their toilets. Prof Jean Venables, CBE and ex President of the Institution of Civil Engineers reckons that the capacity of that sewer was reduced to 5% of its nominal capacity (NB: to 5%, not by 5%). Experts reckon that for this ‘fatberg’ to have grown to such proportions, the sewer must not have been maintained properly for an extended period.  Yet consumers are paying for such routine maintenance; where is that money going?
  29. [29] rather it’s more likely that TW are neglecting their maintenance duty; much like they wouldn’t be interested in fixing clear water network leaks if it weren’t for the regulatory pressure applied by Ofwat. Maintenance merely costs money unless one is interested in long term perspectives, which is typically well outside Private Equity outfits’ horizon (we’re back to the issue of misalignment of interest between the privatised monopoly arrangement and those of the general public).
  30. [30] Source: page 52 (57 on PDF) of TW’s “Needs Report” for the Thames Tunnel, which also mentions that “All options allow very infrequent residual spills to the River Lee at Abbey Mills to protect the tunnel system from high water levels during extreme rainfall events” without quantifying them.  At a public briefing on 11th April 2013, Phil Stride, head of TW’s TTT unit admitted that in order to be able to capture peak stormwater flows, the tunnel would have to be twice as large as its current design, which is simply not viable, both from an engineering (sheer space requirement) and cost perspective.  Scant details are available as to how these overflows will happen and what effect they will have on the river’s habitat.
  31. [31] This is the reason TW now readily admit that without SuDS, “the tunnel’s lifespan will be very limited”.
  32. [32] Source: page 15 of TW’s glossy: “Why does London’s economy need the Thames Tunnel”.
  33. [33] Another example, in Philadelphia, a worldwide leader in sustainable water management, a survey found 32,000 jobs related to GI within a few years of the city embarking on the most ambitious blue-green programme.
  34. [34] This negates another of claim that “decades of studies have confirmed that the TTT is the best solution” – this research, which was conducted in a time when one simply didn’t know better than build more unsustainable infrastructure, is completely out of date.  This is one of the reasons Chris Binnie, who was the Thames Tideway Strategic Study’s independent chairman has urged a rethink.
  35. [35] A “common sense” practice which recommends that issues related to water should be considered as a holistic “big picture” rather than each in isolation.  For example: flooding and drought are both very much related to rainwater and the so-called “natural water cycle”, which is being impaired by excessive development in general and impervious surfaces in particular.  By contrast, the TTT considers only the single issue of sewer overflows (imminently related to rainwater as explained above) and leaves it to other measures to solve the other issues.  In the case of drought, for example, TW’s solution is yet more ruinous and eminently unsustainable infrastructure such as desalination plants.
  36. [36] Washington D.C’s mayor has recently acted to stop two similar tunnel projects, while the city performs due diligence analysis of the perceived superior and cheaper GI solution.
  37. [37] Let’s say for example that its gradient is insufficient and results in blockages or that the it becomes prohibitive to run the energy-hungry (15GWh) pumps required to operate it – a real likely scenario since (1) the UK is headed for an energy crunch within the foreseeable future and (2) the CO2e cost of operating these pumps could easily skyrocket within a decade.
  38. [38] Many of the cities, such as Milwaukee (US), which were early adopters of similar tunnel solutions found very quickly that they had issues – in Milwaukee’s case, they had to shore up the tunnel with a second multi-billion expense only eight years in.  The tunnel is much like a multi-generational mortgage: 14m people are to be hooked on its cost, and any resulting overruns.