Flood risk and cities

The year 2015 ended with a series of storms causing unprecedented flooding in Lancashire, Greater Manchester and West and North Yorkshire. Bridges were washed away and thousands of buildings flooded, with the UK winter storms causing damage estimated to be at least £3 billion.

This figure appears, not as a cost to the economy, but a boost to GDP (which measures transactions) thanks to the spending required to repair the damage. As the current UK Government derives much of its policy from the effective ‘gaming’ of particular Key Performance Indicators of “Economic Health” such as GDP, this is a benefit, although those affected by  losing large amounts of their homes or businesses may see this differently.

So, while there is a strong argument to develop flood defences so that flood damage can be reduced in the future, there are a number of barriers which make this more difficult. The economic argument being not only that flood damage boosts the economy, but also that spending on flood defences requires a high Benefit to Cost ratio to justify them – while 2.0:1 is required for many road and rail transport projects, flood defence schemes now require 8:1.

What seems likely to happen with flooding in the future, and what consequences does this have for our cities?

Rainfall & Drainage

One of the key impacts of Climate Change in the UK is that, as the global climate warms, and warmer air is able to carry more water, almost all climate models predict an increase in rainfall and storm conditions (more heat energy in the atmosphere also causes higher pressure differentials and therefore stronger winds).

George Monbiot has written extensively on how woodland, drainage and watercourse management over the last few years have combined to exacerbate the impacts of more frequent storms, thanks to Government policy and the economic pressures on farmers. Water now drains more quickly into rivers without the benefit of upland woodland in particular to slow its progress and spread the extra water load over a number of days, thereby avoiding flash flooding.

Water Management

In the UK, water distribution is also a major issue – with the South East having the driest climate and a relatively high population density, water is, in many places, a fossil fuel, extracted from aquifers thousands of times faster than it can be replenished, even by floodwaters whenever they occur in the ‘right’ places for this. Areas obtaining their water from reservoirs are at much lower risk of drought with a warmer climate generating more rain storms, and can more easily store floodwater for future use.

Water runoff from hard surfaces flows quickly into storm drains and then into rivers. Increasing car ownership led to gardens being paved over for parking, which worsened floods in 2007 and resulted in a change of Planning regulation. Flood defence programmes often canalise rivers or dredge them, both of which speed their flow.

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How urbanisation and more hard surfaces worsen flooding (Source: Susdrain: The Community for sustainable drainage)

On the other hand, Sustainable Drainage Systems (SuDS) slow stormwater by letting it soak into ground and wetland vegetation, which release it slowly, and green roofs can perform a similar role. Several towns and cities which have developed quickly with poor fluvial drainage (such as Bracknell and Milton Keynes) use networks of balancing ponds to store stormwater before slowly releasing it into the drainage system, as smaller streams and rivers would be unable to take large peak loads without flooding. These ponds double up as park water features and sometimes as boating or watersport lakes. While these are not SUDS themselves, they perform a similar role.

Flood Plains

The Environment Agency divides flood risk into three zones, 1, 2, 3 and 3a, as shown below

Floods - flood zones
Environment Agency Flood Risk Zones

However, the practice of referring to “1 in whatever” years’ flood events or storms has to be called into question when formerly 1 in 100 year events now appear to have much higher frequencies. In any case the Zones reflect relative flood risk and still have value in that sense.

Large portions of some cities lie in Zone 3, as can be seen from the map, including many locations on which development is proposed. In Leeds, much of the Aire Valley Area, including where development has already started, is in Zone 3, as is a large amount of the Thames Gateway area, stretching from London to the far reaches of the estuary in Southend, this map from Kingston University’s School of Architecture & Landscape shows only the London area.

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London Flood Risk (pink) and the Thames Gateway (hatched). Source: School of Architecture & Landscape, Kingston University

The Thames Gateway

With the UK so dominated by London, issues affecting London are widely discussed in other places so are rarely covered here. Its Planning and other initiatives are in many cases wildly divergent from other parts of the UK. London’s greater financial and political autonomy (with its own Devolved Assembly), its role as seat of Government and its dominance of the economy and economic discourse are such that it should be expected to have a long term, financed plan for mitigating the effects of flooding – this being the Environment Agency’s Thames Estuary 2100 Plan of 2012. This revised downwards the former Worst Case Scenario for water level rise in the Thames by 2.5 metres (Page 24), and suggested that “The Thames Barrier will continue to provide tidal flood protection to West London to the same high standard as is enjoyed in all the other areas protected by the Barrier. But over the next 25 years we need to put in place new ways of managing fluvial flooding other than by operating the Thames Barrier” (Page 44)

The strategy maintains that the Thames Barrier will not need replacing until 2070, though this is considered in terms of defence against marine storm surges, rather than fluvial flooding from ‘extreme’ rain storms (which are projected to be normal winter storms in the future). However, its rate of closure to avoid floods has increased significantly as The Guardian reported in February 2015, “The other exceptional element of the 50 closures cluster [December 2013 to February 2014] was that the great majority – 41 of them – were prompted not by tidal surges from the east, but by prolonged heavy rainfall in the Thames catchment area to the west of the capital. The resulting increases in “fluvial flow” downstream created the second type of reason for closing the barrier – protecting vulnerable locations just upstream from Teddington, such as the village of Thames Ditton and the residential Trowlock Island.
These are put at risk when the pressure of the tidal Thames waters arriving from the other direction further boosts already high water levels. But that risk is reduced if, over on the opposite side of the city, the barrier is closed just after low tide. This effectively turns the London stretch of the river into a temporary reservoir with spare room into which the extra fluvial waters can freely pass”

Government’s confidence in rising flood frequencies not being a major issue is such that the largest expansion of development and population in the country has been planned in this very area. The Thames Gateway area covers around 60km (4 miles) of the Thames Estuary, on both sides, and, as Terry Farrell wrote in his book Shaping London, “This is the global-warming frontline; this is the defence zone where the long-term future of London will probably be decided” (Page 84)

“I sat back and looked at the whole of the estuary when questioning the government’s definition of the Thames Gateway project five years ago. It seemed to me that until recently there was a habit of using economic targets as a substitute for vision and planning – to my mind, targets such as the number of houses built (200,000 being the ultimate target), the reduction in unemployment, the creation of new jobs, and the amount of inward investment being attracted did not add up to the same thing as a vision and a plan. So, after much self-questioning and thought on the subject I offered the idea that the core concept should indeed be that of environmental and landscape regeneration as the first infrastructure … This led to a plan being published at the end of 2008, which was generally accepted and supported. It now seems that under the title ‘Eco-region’, a new vision is emerging which to my mind is much more satisfactorily attuned to the issues of this century” (Pages 97-100)

The lack of foresight here was staggering, but as a result, of Farrell’s work, his Masterplan was retrofitted onto the Thames Gateway proposals, providing for wetland green spaces and the shifting around of development to at least some account of vulnerability to flooding. The development is the responsibility of three different agencies in different areas, the London Assembly in London (The London Thames Gateway Development Corporation having been wound up), the Thames Gateway Kent Partnership and the Thames Gateway South Essex Partnership, each with their own masterplans. Development outside London has been slower than anticipated, and perhaps has been scaled down – the Ebbsfleet Garden City has a target of around 10,000 homes, making it smaller than most of the Post-War New Towns despite having the advantage of the out of town Regional Shopping Centre at Bluewater and the High Speed Rail station at Ebbsfleet, both of which could support a far larger population – not to mention its position in the lowest flood risk zone.

Elsewhere

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The ‘viral’ photo from Whalley, apparently showing floodplain land with Planning Permission… (source unknown)

So, while London’s flood defences and forward planning could be said to be woefully inadequate, what hope for the rest of us? A photo of a sign (above) in a flooded field in Whalley, near Rochdale, went viral after the December floods in Northern England. It stated “Development site with permission for 39 dwellings”. It turned out to actually be in Zone 1 (the zone of least concern, in which there is a 1:1,000 or less risk of flooding), and certainly shows Storm Eva flooded land which was not considered at high or even medium risk from flooding. With strong predictions of more frequent storms and flooding in the future, perhaps the Zone boundaries need updating.

What can be done?

Ultimately, the key question is how to respond to the prospect of flooding in Britain becoming more frequent. The late Planning Professor Peter Hall, in his manifesto for the future of London (1963’s London 2000, followed by 1988’s London 2001), advocated a constellation of 25 New Towns around London, and, while sea level rise was not mentioned (let alone the issue of Climate Change leading to more storms and floods), he described a response to one of his proposed sites being poorly drained – “The lights that illuminate the sky to the south mark a new town: Headcorn, started next to the Channel Tunnel High Speed Train route at the same time as Hamstreet. Twenty miles nearer to London, its houses were snapped up by London commuters. Its architects, finding they had to build on ill-drained Weald clay, made a virtue of the fact and designed the town around a series of canals which divide the town into islands” (London 2001: Page 212). Naturally, this is not a new idea at all – Amsterdam is built on boggy ground and all its buildings are supported on masses of wooden piles, with a network of canals fulfilling the dual purposes of transport and drainage.

In some locations, such the Thames as Windsor, secondary channels have been created for the purpose of storing flood water and letting it out into the river slowly, although these have a large land take . Such a scheme was proposed for the Aire at Leeds, but was subsequently cancelled. The story of Pickering in North Yorkshire, which used more low-tech flood defence techniques and didn’t suffer as badly as surrounding towns from the Storm Eva floods is quite interesting, and shows that this approach can also cost less than a heavy engineering one. There has been a counter-argument, showing that rainfall in the Pickering area had been lower than almost everywhere else in Yorkshire, but equally the rainfall in an area of fluvial flooding is less important than how much rain has fallen upstream.

That is not to say that there is no merit in more ‘engineering’ driven solutions, but the short-termism of UK Government thinking and the stop-start nature of investment which this produces doesn’t lend itself well to tackling these issues.

In an environment where Planning is considered to have limited value, never mind its relatively narrow scope and scale in the UK (with no full National Spatial Plan and the elimination of Regional Planning from England in 2010), it is also difficult to see how holistic solutions can be arrived at. Housebuilding is dominated by the construction of standard model houses while flood-prone areas could benefit from designs with more waterproofing and which can dry out quicker, and Planners increasingly have less power to specify such responses. Sustainable Drainage Systems and green roofs are also relatively cheap, and designating floodplain land as sacrificial in times of flood, perhaps with only recreational use, is also possible by rearranging development and green space (as Terry Farrell advocated)

The situation George Monbiot referred to is one where the protection of agricultural land and urban land are pitted against each other, while it is necessary to protect both food supply and the places where people live and greater economic output is produced, much conventional land management practice has been detrimental in terms of water impacts to farms as well as cities. A more holistic approach to water management which can slow the passage of water into rivers, replenish aquifers and reservoirs and ensure we build with floods and water management in mind, This would involve everything from upland woodland management to reducing soil erosion, Sustainable Urban Drainage Systems, green roofs for water storage, building in water-sensitive ways on floodplains (if we must) and potentially sacrificial urban reservoir space, as has been implemented in parts of the Netherlands, where underground car parks can be used as floodwater storage – it’s even proposed as a strategy in Oxford. As with so much else in Planning, one of the key issues is that it requires more coordination and more upfront funding than it appears anyone is prepared to commit.

 

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