Do you live half way up a hill, or well away from rivers and sea? Have you been watching the floods on TV and thinking, ‘Thank God that’ll never happen to me’? Well think again.
Broadly (and I know I’m over simplifying a bit) floods fall into two categories: fluvial, where accumulated water flows into rivers which then burst their banks, and pluvial, where sudden heavy rainfall overwhelms drains, sewers and culverts, flooding nearby properties. To be at risk from fluvial floods, you need to be fairly near a river. Pluvial floods, on the other hand, can happen anywhere.
We think of flooding coming from rivers because fluvial floods tend to be on a much bigger scale and they therefore attract more news coverage. Pluvial floods are usually smaller and more localised. A whole area being submerged will bring in the reporters but a drain overflowing, or a sewer bursting, flooding half a dozen houses, may not even make the local news.
It’s difficult to get accurate figures on pluvial floods because they are sudden, localised and, therefore, often unreported. Some recent studies suggest that, because of the frequency of pluvial floods, over time, they do nearly as much damage as river floods.Two years ago, a report by the Joseph Rowntree Foundation estimated that pluvial flooding accounted for around one-third of the UK’s flood risk. This paper from Risk Management Solutions on the 2012 floods put the figure even higher. RMS calculated that half the flood damage in 2012 was due to pluvial flooding.
In the past, the “at risk” definition commonly referred to properties located in the floodplain or vulnerable coastal areas. However, 2012 demonstrated that high-frequency flood losses can accumulate to significant levels in other regions as well. While 2012 flooding was widespread, little of it occurred along major rivers; much of it occurred on the minor rivers or was pluvial in nature. The high groundwater levels and soil saturation were important antecedent conditions influencing the observed flooding. As the persistent, extreme weather exacerbated these conditions through the year, the reported incidents of pluvial floods increased to become the dominant mode of flooding by the end of 2012. From an insured loss perspective, no individual flood event was in and of itself a major source of concern to the insurance industry. However, taken together, the geographic extent and temporal concentration of flooding led to the second-highest total annual flood losses in the U.K. since records began; surpassed only by the annual losses from the U.K. floods of 2007.
So, although most floods that year were not major events and therefore not newsworthy, their cumulative effect gave 2012 some of the worst flood damage since records began.
Pluvial floods were a significant factor in the 2007 floods. Remember the floods in Hull? This Hull University report explains how rainwater overwhelmed the drains, pumping stations and sewage systems. Its conclusion:
The June 2007 floods came from an unexpected source: surface water flooding. This revealed a major weakness in UK flood defence strategy, which has no capability for forecasting or warning from pluvial flooding. Furthermore, the design levels of urban drainage need to consider the vulnerability of the site. This is especially important for low- lying areas with no natural gravity-driven drainage such as Hull. Finally, the way in which the UK water industry is presently structured, postprivatisation, means that there is no lead agency for urban surface water flood management, although the recently enacted Flood and Water Management Act provides a new framework for responding to urban flood risk.
After the floods of the last few weeks, there is a lot of talk about building defences against river and sea flooding but this is only half the story. Combatting pluvial flooding is more complicated and will require significant improvements to drainage and sewage systems.
Inevitably, the water companies are coming in for a lot of stick over this. Channel 4 has been on their case:
The Environment Agency has taken its fair share of blame for the flooding misery in Somerset , but there is an industry which has escaped criticism. And unlike the quango, it’s not short of a billion or two. Step forward the privatised water industry which has a key role in dealing with our storm and sewage water. In the last six years water companies have made £11 billion in profits from our water bills, surely enough to have stopped its customers from having raw sewage flooding into their homes and down their streets every time there is a heavy downpour.
Dispatches has been investigating the role of the water companies in the country’s recent flood problems and while Somerset have been dealing with record rainfalls and storm surges many homes across the country have been dealing with another consequence of the deluge: sewage flooding into their homes and down their streets.
When it rains heavily, our underground infrastructure can become overwhelmed and raw sewage can get discharged onto our streets , rivers and to a growing number of unfortunate people into their homes. According to the Consumer Council for Water, complaints from homeowners about sewer flooding are up by 50% compared to last year. [My emphasis.]
Private Eye is having a go too.
THE really unpleasant thing about floods, which isn’t conveyed in TV footage of people collecting groceries by canoe, is that they turn streets and homes into open sewers. It’s disgusting, a severe health hazard and it takes weeks to get rid of the stench.
Londoners have so far been spared shit in the streets.
But after heavy rain the Victorian sewer system cannot cope. On some 50 occasions in 2000, a year of exceptionally heavy rainfall, London’s sewer system was in danger of overflowing.
The water companies argue that at least some responsibility must be borne by customers who concrete over their gardens and throw all sorts of junk down the drain which, eventually, clogs up the sewers. There may be some truth in this but, regardless of who is to blame, the evidence suggests that sewers, drains and the infrastructure for managing rainwater floods will need to be upgraded over the next decade. It wasn’t designed to cope with today’s population, lifestyles and, in all likelihood, increased rainfall.
These days, it’s not just tree-hugging hippies who think the climate is changing. Defence strategists, security analysts and the insurance industry are pretty much convinced too. If generals, majors and the gnomes of Lime Street are preparing for it, the rest of us should take it seriously too. The consensus among scientists seems to be that winter rainfall, and therefore flooding, will increase in Britain over the next few decades. If pluvial flooding is a problem now, it’s one that’s only going to get worse.
As with so many things, there is a class element to all this. In news reports, we usually see large riverside houses flooded but the Joseph Rowntree Foundation found that those in the most deprived areas are most at risk from pluvial flooding. Many of these areas were developed during the industrial revolution. They tend to be on low-lying land and, even where the housing stock has been modernised, the drains and sewers often haven’t.
Fluvial flooding is shouty and makes headlines, while pluvial flooding is quiet and insidious. If we are going to get a lot more rain, flooding will become an annual problem in more places. Not all of those places will be by rivers or on the coast.vial flooding makes headlines, while pluvial flooding is low key and insidious. A lot more people will be at risk from flooding even though they are nowhere near a river. Yes, flood defences need to be improved but that’s only half the story. Our sewers and drainage systems will need some serious work too.
Declaration of interest: Our house was caught by a pluvial flood after a downpour overwhelmed the drains and sewers in the neighbouring street. We had to move out for nine months while the damage was repaired.
Update: Quoting research by the Environment Agency, Zurich Insurance reckons the risk from pluvial flooding is even greater than that from river and sea floods. They also have a gentle pop at the water companies.
In the summer of 2007 following a period of persistent wet weather, Hull was one of the many towns and cities across England to be affected after bursts of heavy rainfall triggered multiple flooding events and saw insured flood losses total £3 billion across the country – the largest amount ever paid out by UK insurers.
And this danger is only likely to get worse due to a combination of climate change as well as an expected increase in the UK’s urban population, planning regulations that encourage building in flood risk areas and as-yet limited investment by water and sewerage companies to update Victorian-era systems, notably in London.
Graphic via Zurich Insurance
Update 2: The FT’s Jim Pickard pointed out that this year’s floods have still not affected anywhere near the number of properties as those of 2007.
Not to play down impact of the floods on victims but so far 5,800 homes flooded…..against nearly 60,000 in 2007 http://t.co/5RIFlgz9dK
— Jim Pickard (@PickardJE) February 12, 2014
Most of the damage in 2007 was caused by pluvial floods.
Update 3: Colin Wiles argues that we should build more houses, not fewer, in places like the Somerset Levels:
After all, if this is marginal land, what better use is there than housing? If that sounds counterintuitive, look again at Amsterdam. It was created out of a similar landscape and sits at or below sea level and yet flooding is rare.