Urban flooding

Assembly 2014: Blue-green infrastructure and urban flooding

One of the problems with flooding is that it takes many forms. Coastal flooding you can understand – if you live on a low-lying coast and it’s stormy, there’s a chance that the sea may reach your property. Similarly, if you live on the banks of a river, you can see how a river might break its banks and flood neighbouring land.

Pluvial flooding seems to be the most difficult type to get to grips with. Pluvial means ‘due to the action of rain’; so pluvial flooding results when rain falls so heavily that the local drains can’t dispose of the water fast enough.

The Flood Risk session at the ARCC Assembly looked at all sorts of flooding, but one project had a particularly interesting view on pluvial flooding. The Blue-Green Cities project looks at how we might be able to recreate the natural water cycle in our cities. In natural systems, the rain falls and is either absorbed directly into the ground or transported away down streams and rivers. Some of it sinks through the soil to become ground water, and some of it evaporates into the air to fall again elsewhere as rain. The rest eventually reaches the sea, where it evaporates and later falls as rain – starting the whole cycle over again.

In our urban areas, the rain can’t sink into the ground as it’s mainly covered with concrete and buildings, so water is channelled into pipes in the hope that it will flow away.

The Blue-Green concept proposes a different approach – have more absorbent surfaces, recreate natural channels for water to flow through, and allow it time to evaporate back into a more natural water cycle. This idea exposes many challenges, not least of which are arguments that the land in our urban areas is simply too valuable to ‘waste’ on green stuff.

However, we seem to be experiencing more extreme rain storms and more intense floods. Repairing the damage costs huge sums of money, with many small businesses never recovering from a flood. And that’s not taking into account the stress and health impacts which society does not seem to consider.

In the long term, there must be a better way than just building bigger and bigger drains to pass the problem onto someone else. Maybe, just maybe, the Blue-Green approach is the way forward for our urban areas. Surely it’s worth a try.

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