Flooding needs big ideas: five solutions

14 February 2014

If we are to take the potential impacts of climate change seriously, we need bigger solutions to flooding, writes Ben Mitchell.

Ben Mitchell

The recent and relentless floods have led to calls for urgent action, both in the media and from affected communities. But some of the solutions proposed are knee-jerk reactions that may not be sustainable in the long term, they will only tackle low order flooding in the short-term. Instead, we need to think strategically.

The good news is that, despite flood levels on the east coast exceeding those of 1953 when several hundred people died in Britain, the vast majority of the Environment Agency’s defences have held. But we still need to plan ahead.

It helps to properly understand the underlying causes of recent flooding which are hardly typical: tidal surges resulting from combinations of astronomy and meteorology.

The beginning of January saw the usual spring tide of a new moon combining with the perigee, when the moon is closest to the earth, and the perihelion, when the earth is closest to the sun. This resulted in a boost to the gravitational forces thereby amplifying the usual spring tides which occur twice monthly at the full and new moon. A low pressure weather system from the Atlantic with its associated strong winds, brought to our shores by the jet stream being pushed further south, strengthened the tides even further.

Over the longer term, sea levels are rising, threatening our coastal communities. Surface water (pluvial) flooding is also getting worse, this is local flooding when drainage systems are unable to cope with high intensity local rainfall. Both rising sea levels and high intensity rainfall are some of the predicted impacts of climate change. Below are five possible solutions:

1. SuDS

Sustainable Drainage Systems (SuDS) will play an important role in the future but they are not a panacea and cannot necessarily be adopted as a blanket approach. At the downstream end of some medium-scale catchments, the delayed release of surface water can actually increase peak flows and make flooding worse. Furthermore, after prolonged rainfall, if the ground is saturated then the water has nowhere else to go and the implementation of SuDS could result in flooding at source. Soakage is also not practical for the many areas which are underlain by impermeable clay.

2. Planning for strategic infrastructure

If climate change impacts do their worst, then we may well be forced into providing major drainage infrastructure and for this we should be planning now. There must come a point when we can’t keep holding the water back in storage ponds or trying to soak it away into saturated soils.

It makes sense to learn from tropical countries which experience high intensity rainfall during typhoons. Many such countries have high-capacity drainage channels which normally carry only low flow but will be flowing “bank full” in times of a typhoon. If we are going to need these, we should start planning now for “reserved corridors”, at least in our urban design for future generations.

Each planning authority has strategies and action plans for its administrative area; these documents generally just repeat national policy for development in floodplains and lack bold new “strategy”. In this green and pleasant land we may not have the appetite for the unsightly large capacity flood channels seen in Los Angeles. But it is in these documents that authorities should be planning the future provision of strategic drainage and flood defence infrastructure.

Different solutions are needed to our flood problems.Photo: Martin Pettitt/Flickr

3. Building on floodplains

Of the strategic infrastructure we do have, a chronic shortage of housing in the UK means that, inevitably, some sites in lower risk flood zones will be needed for development. Technically, it is not difficult to achieve safe floodplain development by employing design solutions such as raising platforms. While these solutions can be expensive, this should be offset by floodplain land having limited monetary value otherwise.

4. Managing retreat for some communities

A tough solution. Some places may need to be abandoned to the sea, as has happened on the east coast already, or to inland flooding. It will not be cost-effective or practical to maintain defences for less productive agriculture or even small settlements, either on the coast or on areas below sea level, when defences need to be paid for elsewhere. Taxpayers may not be prepared to keep on paying for protecting these areas without economic justification.

5. Taking climate change seriously

The government needs to take the lead on climate change. In its bid to revive the economy before the next election, it has put the green agenda on the back burner.

The Intergovernmental Panel on Climate Change’s recently published report, Climate Change 2013: The Physical Science Basis should concentrate minds. It says that “continued emissions of greenhouse gases will cause further warming and changes in all components of the climate system. Limiting climate change will require substantial and sustained reductions of greenhouse gas emissions.”

It is clear from this winter’s events that tinkering round the edges is not enough. We owe it to future generations to think big and to get it right.

Ben Mitchell is a partner at Peter Brett Associates

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