Flood warning
The densification and expansion of infrastructure and property in high risk areas is already increasing the threat caused by severe flood events. Unthinking adoption of a "business as usual" approach will not solve these issues, so how should the industry respond? Here, Mike Woolgar, managing director for Atkins' environmental and water management business, examines the major challenges being faced by the worldwide water industry.
Anyone who has had their home flooded knows what a terrible effect it has on one’s life, health and feeling of security: the home has been invaded by an irresistible, smelly and uniquely destructive force. Those who are comprehensively insured can recover their belongings and get back to living relatively quickly, although the psychological effects can take much longer to drain away. For those who are uninsured, and there are many of these, the recovery period is so much greater. Around the world, the poor, the less economically resilient, tend to live on the most marginal land, and that includes land prone to flooding.
There are three main types of flooding:
- Coastal: when high tides, low pressure events, strong winds and more topically tsunamis occur alone or in combination, overwhelm the coast and flood the land behind. Periods of flooding reflect tidal cycles.
- Fluvial: when river flows from high rainfall and/or snowmelt cause rivers to overtop their banks and inundate the floodplain which may or may not be built up. Floods can take days to rise and fall or minutes in small catchments like Boscastle.
- Pluvial: when high intensity rainfall in urbanised areas runs quickly off the roofs and paved areas and the resulting flow overwhelms the road and other local drainage systems. Typically these vents have rapid flood rise and relatively quick fall after the rain stops.
Damage and devastation
Whatever the type of flooding, the water is not clean and healthy, frequently carrying sewage, industrial waste, flotsam, sediment, farm waste and other undesirable materials. Depending on the depth of flooding, the speed of rise, the duration and the flow velocity, outcomes can include death, damage, decay and devastation. Farmland can be ruined; roads inundated for days thereby preventing commerce, access for emergency services and normal social contact; power and other utility systems can be flooded or threatened causing supply outages and necessitating huge emergency logistical exercises to supply clean water. We saw all of this in the UK in 2006 and 2007 and the UK has a temperate, benign climate. In Jeddah in 2009 there were over 100 deaths in road underpasses as people were trapped and drowned in their cars by flash flooding. In Pakistan the floods in 2008-09 destroyed roads and the economy in the highlands, and the 2010 floods in the heavily populated areas along the Indus are still draining away in some areas.
Returning to the benign UK, what is the cause of the problem? Why has the UK Government identified inland and coastal flooding as 2 of the top 13 national risks (National Risk Register of Civil Emergencies, Cabinet Office, 2010)?
Our economy is increasingly urban in nature and we build much of the new infrastructure where the urban nodes are. As the amount and value of housing, factories, retail properties, roads, cables and all the paraphernalia of modern life increases in these areas, so the risk – evaluated as the cost of damage suffered and the probability of such damage occurring – increases. This is the case even in the absence of any climate change effects. This is why the Environment Agency has for years been cautioning against further development in floodplains and this is why the Environment Agency now has the power to object to planning proposals which could further increase risk. This is also why the Pitt Report recommendations and implementation of the Flood and Water Management Act are important, reflecting the need to co-ordinate management of urban flooding whether fluvial, coastal or pluvial.
If we add in the impact of climate change with sea levels already rising and expected to rise faster and further, and with rainfall patterns expected to become more seasonally exaggerated in many locations, the risk is increased still further as probability of events increases.
A complex environment
So what can we do? Obviously, wholesale removal of urban infrastructure to “safe” zones is not economically justifiable and is probably socially unacceptable – given current predictions of climate variability. This is not to say that it has never happened – there are some small towns in the US which were relocated many years ago – but a more reasoned response will include better assessment of risk, review of new development proposals and ensuring that any that do proceed are designed and built with flood resilience and flood impact taken properly into account.
As a social and economic problem, with uncertain science and uncertain hydrology, flooding is not just a “hard” engineering problem although of course some solutions have hard engineering solutions: sea defences are frequently concrete and steel to resist the continuous battering that they get. Flooding is also spatially complex with effects sometimes very localised and sometimes very broad. The impact of particular structures or topographies can have significant effects locally or elsewhere and new development can be built where it can itself be at risk or can exacerbate risk to others. Planning has to be for flood management rather than just flood defence. It needs to be done at catchment or “landscape” scale to be sure of capturing all the influences and impacts. It requires a blend of skills from a range engineering types: scientists, economists, social science working together to elicit sustainable and workable solutions amid a large set of geographical, legislative and other constraints. It will also require good communication skills so that the numerous stakeholders can come to understand their roles and responsibilities in this increasingly complex environment.