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Floating on a new wave

Last week flooding experts from across the UK gathered in London to form a united view on the government’s future flooding strategy. Mark Hansford reports.

Shortly before Easter the government is expected to publish one of its most widely anticipated pieces of legislation in years. Its aim is to prevent a repeat of the devastation of summer 2007 when exceptionally heavy rain caused widespread flooding.

This affected 55,000 properties, led to the rescue of 7,000 people and contributed to 13 deaths. Eighteen months on, the bare facts emerging from the 2007 floods remain staggering – the country saw the largest loss of essential services since the Second World War, with almost 500,000 people without mains water or electricity. Transport networks failed, a dam breach was narrowly averted and emergency facilities were put out of action. The insurance industry expects to pay out over £3bn as a result of the floods, making the UK floods the most expensive in the world in 2007.

Much has happened since summer 2007. In February 2008 the government published its Future Water strategy for England. This explained the importance of water in our society and the way in which the government will manage this important resource. Shortly after, the independent Pitt Review from Sir Michael Pitt highlighted the need for a single Act of Parliament to bring together the disparate pieces of legislation governing the issues relating to flooding and flood defence responsibility.

In May’s draft Queen’s Speech, prime minister Gordon Brown outlined plans for a Flooding & Water Bill to act on the review and on issues raised in the Future Water strategy document. This Bill represents a once in a lifetime opportunity to put in place systems that will actively implement new thinking in flooding and water management and support best practice. It is that important.

Future Water and the Pitt Review were the subject of considerable consultation, and as a result it is expected that no consultation document will be prepared before the draft Bill is published. So the industry needs to be ready when this happens – the Bill is expected to appear before the Easter recess. It will then enter formal consultation and pre-legislative scrutiny in the early summer. At this point, stakeholders will be expected to present their views before the Bill is introduced to Parliament in the 2009/10 session.

Last week, water and flooding engineers congregated in London at the Chartered Institute of Water & Environmental Management (CIWEM) winter conference in an attempt to form a common view, ahead of the Bill’s publication. Top of the agenda was Pitt’s recommendation – adopted by government – that local authority engineers take the lead on flood defence. Around £15M has been allocated for this, but many feel that is not enough. "The £15M of funding to establish the new local authority powers seems insufficient to build up the necessary expertise and resources required," says Hydro International director Alex Stephenson.

Pitt called for a revival in local government technical skills with much higher pay scales for public sector flood engineers. Council leaders have backed the move to give local authorities a stronger leadership role in flood prevention, but say that they are under-funded and under-staffed. A joint survey of 257 councils in England before Christmas by the Local Government Association and the Department for the Environment, Food and Rural Affairs found that 60% of councils lack the money to fulfil their flood risk responsibilities. It also found that a quarter have had difficulty recruiting and retaining technical staff.

Last year Pitt told NCE he recognised that this would be a challenge in the face of dwindling engineering departments in local authorities where much of the engineering specialism "is now limited to highway engineering".

Aside from local government resourcing, there is concern about the engineering approach to flood defence, in particular the vital role of sustainable urban drainage systems (SUDS) and the ability of local authority engineers to properly understand them. "One key danger is the enduring misinterpretation of SUDS, which effectively limits its adoption to natural space-hungry above-ground solutions, such as swales and ponds, and misses out on opportunities for using hard engineered storage, infiltration and attenuation technology where appropriate," adds Stephenson, who also chairs trade association British Water’s SUDS group.

"To achieve effective and workable flood management in the future is going to require significant changes in the Environment Agency, local authorities and water companies. But there are still serious concerns in the industry that the new arrangements could remain unclear, over complex and with duplicated responsibilities," says Stephenson.

"A consistent, simple and streamlined solution is required, based on an open approach to sharing information and agreeing what defines a drain or sewer. Work to prepare for these changes can’t wait for the Bill to become law. It needs to begin straight away, supported by training and funding," says Stephenson, summing up the mood of the CIWEM conference.

"Sound SUDS principals also need to be applied to the government’s commitment to remove the automatic right of developers to connect to the public sewers. The problem is that using infiltration and soakaways is simply impractical for many ground conditions. The proposals need to embody the use of appropriate storage and attenuation technologies either to slow flood waters down before they enter the sewers, or to deal with the increased loads of stormwater locally. Even rainwater harvesting could be considered on new developments as a means of holding back rainwater during peak storm periods," he says.

Everyone will be looking to the Bill to see how it tackles these engineering and resourcing issues. Its success in doing so will determine the government’s ability to head off another 2007-style disaster.

SOLVING THE PROBLEM
Government is not asleep to the threat of stormwater flooding and has, in the last six years, taken several steps towards addressing it, starting in 2002 with Approved Document H.

This changed the hierarchy of drainage and drainage design considerably and introduced
the concept of sustainable urban drainage solutions (SUDS).

SUDS aim to reduce the volume of run off water reaching sewers and watercourses immediately after heavy rain. They fall into two main categories:

1. Source control and prevention techniques
These are designed to reduce the volume of water discharged from a developed site. They can help to restore underground water resources and include green roofs, permeable pavements, rainwater harvesting and infiltration trenches and basins.

2. Permeable conveyance systems
These channel the run off slowly towards watercourses through a process of filtration and storage in ponds or lakes where it can be slowly absorbed into the ground or evaporate. Such systems include filter drains and swales (long, straight grassy depressions).

SUDS can be incorporated at the following different levels:

  • At an individual property level (for example water butts, green roofs and permeable driveways).

  • At a community level (for example swales, detention basins and porous paving of highways).

  • At a strategic level (for example strategic balancing ponds and wetlands).

In all three cases, debate has raged ever since their introduction over the perceived predilection towards above ground options.

In theory, SUDs employ a whole suite of techniques to effectively manage drainage at source. But in reality, SUDS are seen as swales and drainage ditches acting as stormwater attenuation ponds. Development has been slow with water companies reluctant to adopt them and developers unwilling to waste valuable land installing them. The alternative is below ground storage based on modular tanks or large diameter pipes. Both have advantages and disadvantages:

Above ground (soft) SUDS
Pros

  • Ease of construction (generally only earthworks required)

  • Ease of access for maintenance

  • Natural treatment

  • Encourages biodiversity

Cons

  • High land take

  • Potential eyesore and health and safety risk if not maintained or abused. Can be abused by flytippers

  • Site topography and conditions can limit functionality

  • Lack of designer and contractor expertise

Below ground (hard) SUDS
Pros

  • Minimises space required

  • Can use land above

  • Protected against misuse or vandalism

  • Can retrofit

Cons

  • Water treatment for discharge into water courses requires ancillary components

  • Greater maintenance expertise required as they are confined spaces

  • Site conditions can limit functionality

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