Floods kill 10,000 people a year worldwide. According to aid agencies, they account for over two thirds of the annual average of 211m people affected by natural disasters. They cost around US$7bn a year, a third of the natural disaster total.
Unfortunately, global warming and the continued attraction of development in flat, low-lying, waterfront areas mean that the world's exposure to flood risk is increasing. Certainly this is the recent experience of Britain, which suffered its most extensive flooding on record in autumn 2000, with total losses of around $1.5bn – about $0.7bn of which was insured.
Recorded rainfall in October and November was the highest for 270 years and resulted in 10,000 properties being flooded. The event was a severe jolt to the British economy and resulted in a plethora of reports, recommendations and initiatives.
Quantifying the national risk
Following the floods, the UK government commissioned a report on the national assets at risk from flooding. The National Assessment of Assets at Risk from Flooding and Coastal Erosion was published in September 2001. It confirmed that about 10% of the population of England and Wales – some 5m people in 1.9m homes – live in flood-risk areas.
A positive outcome of the report was that previous investment in flood and coastal defence was proved to have reduced annual average damage from a potential level of $5.2bn to $1.2bn – which the politicians naturally claimed as an impressive rate of return on taxpayers' investment. However, the report also showed that current levels of investment were insufficient to replace assets as they reached the end of their useful life, suggesting that annual average damages would start to increase again
Waking up to climate change
The Government's Environment Agency is the main organisation responsible for reducing flood risk, with over 5000 staff involved in planning, building, repairing and operating flood defences.
Its own report on the lessons learned from the autumn 2000 floods acknowledged that the event was a warning of the impact of climate change – which over the next 75 years could increase the risk from flooding in parts of Britain as much 400%. It acknowledged that future flood risk management must consider the effects of similarly extreme events.
The Environment Agency noted that some flooding occurred from sources other than rivers, such as storm sewers, and in places with no previous history of flooding. This led to public confusion about who was responsible for what – something which is now being addressed.
Need for greater awareness
It was acknowledged that flood warnings could be more effective, and that the population should be informed beforehand, so they knew what to do when a flood warning was issued. The agency now intends to invest more than $150m in flood warning systems over the next ten years, and will run repeated flood awareness campaigns to reinforce the message that floods don't just happen to other people.
It was also acknowledged – perhaps for the first time – that there are many locations in Britain where engineering solutions are impractical, and others where permanent work could lead to significant damage to the environment. In these areas it was decided that a form of grant or incentive should be considered to encourage appropriate local flood protection measures.
The agency concluded that decision-making processes involved in flood defence investment must take into account the wider issues surrounding an integrated risk management framework. These included greater consideration of social and health impacts, and consistent standards of defence within each town. Indeed, the Government has recently published new guidance for planning authorities when considering applications to ensure they think carefully about the risk of flooding before allowing development to proceed.
A call for a doubling of investment
The most challenging set of recommendations for change came not from the Government or the Environment Agency, but from the engineering profession itself. The report by the Institution of Civil Engineers, Learning to live with Rivers, examined the UK's existing flood defence infrastructure and recommended that the current level of capital investment – around $120m a year and equivalent to 0.5% of replacement cost – should be doubled. It also called for improved analysis of flooding probability, better flood resistance in new buildings, a single flood protection programme and a consolidated executive agency capable of providing a one-stop shop service.
The report emphasised that the human distress and health damage caused by flooding had been overlooked in the strictly economic approach to assessing the benefits of flood mitigation, and argued that the human cost should be built into future benefit-cost assessments. It noted that the flooding of houses with sewage from overloaded sewers was even more distressing than surface water flooding and posed a considerable health risk.
Involving local communities in preparing emergency plans was suggested as one way of raising flood awareness among householders and businesses at risk. This should also include planning and resources for recovery from flooding. Greater awareness of flooding could also be achieved through the publication of data by transport authorities, which would commission and publish flood-risk surveys of flood-prone routes or locations, especially where heavily trafficked routes are capable of being severely affected.
In particular, Learning to live with Rivers recommended that using return periods to communicate flood risk was misleading, as people might think that, once they had experienced one 1-in-100 year flood, they would not suffer another in their lifetime. Gambling odds are better understood by the public, so a 1-in-100 year flood would be better communicated as a 100-1 chance flood – reinforcing the fact that the odds remain unchanged regardless of recent events.
The report also recommended that the country's archive of daily rainfall be fully computerised and the resulting files made freely available in the public domain.
A National flood management agency?
On a strategic level, the report called for consolidation of the responsibility for national flood risk management around one executive agency with enhanced supervisory powers over the various operating authorities. It would have resources allocated directly from Government and have responsibility for spending prioritisation, preparation and implementation of flood management schemes.
The engineering profession is, however, fully supportive of the Government's new initiative to prepare catchment-wide flood management plans for all 80 catchments in England and Wales. These will enable flood-control measures to be properly integrated through the use of computer-based models, which can be adjusted to allow for future changes in climate and land-use. This is in contrast to the relatively inflexible approach in the Government's current flood estimation guidance.
Learning to live with Rivers concluded that it was vital that rivers were provided with flood storage areas – even at the cost of abandoning homes and businesses in flood plains. It also reminded everyone that 'floods can only be managed, not prevented'.
Simon Fullalove is a civil engineer. Tel: 020 8744 2028, E-mail:
simon@fullalove.com.
