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Your View | What is the water supply problem?

Water cropped

Total water supply (including leakage) in England and Wales is only around 7% of the average water resource. Virtually all of that 7% is returned, either as leakage or after use. We just move water around, in time and place. There are environmental gains and losses depending on the where and when of abstraction and the where and when of returns. But there is no question of any absolute shortage of water – just shortage of enough storage to sustain supply through the dry times.

Meanwhile, leakage control is expensive, never-ending, and suffers diminishing returns. There will always be a financial optimum where it starts to be cheaper to provide “new” water than to reduce leakage. This would be Ofwat’s ideal target – but of course it needs adjusting for environmental effects.

So what are those effects?

In the dry South East, most of London’s water and about two thirds of Anglia’s comes from river abstractions at or near their tidal limits. Tidal limit abstraction has zero effect on the fresh water environment, and wherever water is returned upstream (by leakage or after use) the result is environmental gain, increasing low flows in the receiving river. In such cases why on earth would we want to drive leakage below the financial optimum?

In stark contrast, groundwater abstractions are intrinsically damaging – witness the state of many chalk streams. In groundwater dependant areas, such as much of the Southern region, there is a real case for greater spending on leakage – but even here, might it not be cheaper, as well as more reliable, to substitute winter water via reservoirs for the offending groundwater abstractions?

And in general, why are we in such resolute denial of the value of returning flows, including leakage?

  • David Evans (M), Worcester, davidevans.water@btopenworld.com

Your feature on water resilience (New Civil Engineer, last month) is welcome but surely incomplete. For England and Wales, it concentrates only on domestic/household use, say 3bn.m³ per annum. It omits industry and direct abstraction. The Department for Environment Food & Rural Affairs’ figures for 2006/07 in millions of cubic metres per year are (approximately):

  • Industry including agriculture commerce, power and manufacturing – 1,300m³
  • Leakage – 1,250m³
  • Direct abstraction across all sectors – 6,500m³ (of which a large amount is probably returned to the river system, for example cooling water from the power industry).

So concentration on domestic use/waste is important but misses the whole picture.   

 It should also not be forgotten that the worldwide water required to produce England’s imports of food and goods is estimated to be very much higher than, and in addition to, these figures.  

  • Edward Hepper (F), Uplands 61 Queens Road Alton Hants GU34

It was with a feeling of déjà vu that I opened the feature on water resilience (New Civil Engineer, last month). There are so many parallels with the 2012 drought, and so much of the same language. In 2012 the ICE State of Nation: Water reported that on a scale of one to 10, UK’s water security was only 4; a rating that reflected direct water use in UK, and indirect water use embedded in food and goods imports. The ICE went on to recommend universal metering (at the time said by government to be unnecessary), raised awareness in society of the role played by water, and development of new supply schemes for households, industry and agriculture. The report was reviewed by the government but the response given to the ICE was essentially “we’ll call you”. A wet autumn and winter followed and all thoughts of water security were replaced by those of the impacts of flooding.

So here we are again with the National Infrastructure Commission (NIC) referring to the “limited ambition” of our regulators and water companies to improve water security, and promoting a suite of storage, transfer, and re-use schemes. Globally, the results of Nasa’s research from the Gravity Recovery and Climate Experiment show what is described as “major hydrological change” as precipitation and river flows become more variable, and as ground water depletion accelerates.

I ponder, though, whether anything game-changing can happen when our nation, through its water regulators, continues to focus on keeping the price of drinking water as low as possible, and as we continue to depend on water across the globe to support our food and other import needs. The water discourse in the UK remains largely one related to water company ownership, domestic water prices, and drinking water system leakage. While I welcome the NIC’s views, I suspect that the Treasury’s mantra to keep the domestic water price low, and the arrival of autumn rainfall, will mean that we will continue to sleep-walk into an insecure water future.

  • Michael Norton (F), michael.norton@nortonwater.com

 While your editorial is spot on in its thinking about water resources, especially in the South East of England, the more detailed articles and associated diagram simply illustrate the narrowness of the thought processes involved (New Civil Engineer, last month).

Leakage does not always affect the available resource; in inland areas it simply recharges the groundwater and in some coastal settlements it is the only barrier to saline intrusion. Meanwhile demand management is unlikely to solve the problem within any reasonable timescale. And, with the exception of Thames’ proposed reservoir at Abingdon, there is no need for new reservoirs in England; reliability can be more economically achieved by inter-catchment raw water transfers which, in any case, are more flexible.

The potential costs (at £20bn) are grossly overstated. A functional water grid could be built for not much more than Thames Water is about to spend on its Tideway project.

Flawed design competitions

For several years you have reported on the design competition, then the winning entry and finally the successful planning application for the new footbridge at Tintagel Castle. The winning entry has been described in adulatory tones as “two 30m cantilevers reaching out and almost touching in the middle….” and the planning submission written by the architect states that “the new crossing is not a single bridge but two independent bridges springing from either bank and almost touching in the middle”.

This feature was clearly one of the key reasons why the design was selected as the winning entry – the competition entry said that there would be a clear joint between the mainland and island halves and that the narrow gap between them represents the transition between the mainland and the island, here and there, the present and the past, the known and the unknown, reality and legend.

From the very first time I read this description it was immediately obvious that it would not work and it would not be built with this design feature. A gap that opens up horizontally from 5mm in extreme summer to 85mm in extreme winter is only the starting point of the practical problems. The real issue is the fact that the two halves move laterally and vertically apart when one span is loaded and the other is not and this would be a significant health and safety risk to users. It is also bound to be far more flexible as two independent cantilevers and would no doubt encourage some members of the public to see how much they could make it “move” in the middle.

Why am I therefore not surprised to find that, buried in the fine print of the planning application, is the statement that “a pair of 40mm diameter pins between each half ensure that the bridge halves are aligned vertically and laterally”. So in spite of all the hype and all of the publicity the bridge is actually a single span with a pinned movement joint, and is not two independent bridges at all.

It is a salutary reminder that architects are not engineers and should not be allowed to misunderstand, and more importantly misrepresent, the fundamentals of bridge design.

  • John Roberts (F), johnm axwellroberts@hotmail.com

Cladding responsibility

I must warn that Lord Denning’s comments on the responsibility of local authority building control officers were not overturned by the House of Lords, contrary to what is often said by lawyers, and repeated in Peter Williams’ letter (New Civil Engineer, last month).

The belief that the House of Lords overruled its decision in Anns v Merton by its judgement in Murphy v Brentwood District Council arises from the inability of most lawyers to understand soil mechanics. In Anns v Merton, trenches for the strip foundations were not dug deep enough, so the soil foundation failed causing the structural foundation to fail (ie the structure itself was not defective, the soil resistance was too low). In Murphy the structural raft failed, not the soil (ie the structure itself was defective at the outset).

In law, “damage to property” can lead to damages in tort, whilst “pure economic loss” cannot. “Damage to property” means damage to other property, not to the very product which was defective at the outset (D&F Estates Ltd v Church Commissioners for England). In both Anns and Murphy the product at the centre of the case was the building structure.

This appears to lead to the position that building a tower block with highly inflammable cladding will not give grounds for tort against the regulating authority, while destroying the integrity of an existing structure’s fire protection by applying the same cladding will.

  • DR Carruthers (F), carruthers365@btinternet.com

Why are we so steel and concrete dependent?

I was very interested to read the debate about the construction industry’s carbon footprint (New Civil Engineer, last month). All I can say is that until the industry reduces its dependency on steel and concrete, no significant reductions can be achieved. All other industries have stopped using these materials in favour of fibre reinforced plastic (FRP) composites decades ago for pure commercial reasons.

We need universities to add this subject to their courses and structural engineers to develop their skills in FRP composite design.

We have just delivered our tenth FRP composite footbridge deck and the demand from local authorities is growing rapidly as they recognise the significant benefits in terms of cost, durability, speed of installation and sustainability.

  • John Drewett, Lifespan Structures, Basepoint Havant,Harts Farm Way, Havant, Hampshire, PO9 1HS

 Small is beautiful

 Peter Williams’ comment on value engineering is interesting (New Civil Engineer, June). “Value engineering” is now considered to be equivalent to “cost engineering”: using ingenuity to reduce costs, but it was not always so. The term, as originally derived by Larry Miles in the 1960s, meant “using ingenuity to discover all the values inherent in a product” and thus, in his particular case, determine whether investment would be worthwhile in the associated manufacturing process. “Value” is about much more than money: for civil engineers it is a crucial aspect of how we should consider both what we do and the processes by which we do it in terms of the outcomes for society as a whole. It is a pity that “value” seems to have lost its value.

  • Nick Tyler (F), Chadwick professor of civil engineering, director UCL Centre for Transport Studies, UCL, Gower Street, London WC1E 6BT

 

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