Flood prevention before flood defence

As Sheffield breathes a collective sigh of relief that the new flood defences along the Don mainly held back the torrents, communities further along the river are not so lucky.  The barriers pushed the problem further downstream, so now the unfortunate residents of Fishlake and others around Doncaster and Rotherham have been forced to leave their flooded homes.

Flood at Fishlake near Doncaster, November 2019

Climate scientists have long been predicting more extreme weather at more frequent intervals. South Yorkshire is now acutely aware of what it means to be in a climate emergency. The science is simple.  As the atmosphere gets warmer it holds more moisture. The intensity of downpours depends in part on how much water the air can hold. The rate of evaporation from the ocean is increasing as the world warms. Think about heating a pan of water on your cooker – the higher you turn the dial, the faster the water evaporates. The same thing happens with the planet, and globally, this higher rate of evaporation contributes to more extreme rain.

The planet is continuing to heat up at frightening speed. Here are some recent records.

1.         hottest June ever: 2019 

2.         hottest July ever: 2019

3.         hottest August ever: 2016

4.         hottest September ever: 2019

5.         hottest October ever: 2019

6.         hottest summer ever: 2019

7.         world record hottest month: July 2019

It will be no comfort to the people of Fishlake that people all over the worldhave been suffering from extreme weather.

In Australia they are experiencing their worst ever bushfires.

Fourteen Southern US states are in a “flash drought” that’s cracking farm soil, drying up ponds and increasing the risk of wildfires. A flash drought is the rapid onset of drought driven by abnormally high temperatures and winds as opposed to conventional drought, which is mainly driven by lack of rain.

In North and North East India floods forced more than three million people from their homes in July. In Nepal and low-lying Bangladesh 76 people died after days of heavy monsoon rains. Worst affected was the northern Indian state of Bihar, where some 1.9 million people fled their homes due to rising waters.

But things will get worse. A terrifying interactive map4 is doing the rounds on Twitter showing how the seas will rise as the climate continues to heat. The map reproduced here shows the areas with a 20% annual chance of flooding by 2050 if we continue to pollute our planet. This is not scare-mongering, but a scientific paper published in October 2019 by Climate Central. The authors state that “As a result of heat-trapping pollution from human activities, by 2100, areas now home to 200 million people could fall permanently below the high tide line”

Map of Humberside and South Yorkshire showing areas with a 20% chance of annual flooding by 2050 if we continue with business as usual.

So what are we to do? We need to treat this as an emergency and implement rapid ways to reduce our greenhouse gas emissions to zero.  We need to start mopping up some of the excess carbon in our atmosphere by planting trillions of trees.

To reduce the threat of flooding in Sheffield, the first thing we need to consider is what happens to rainfall when it falls on the moors? We can learn from the town of Pickering, where people have worked with nature and not against it. Pickering is at the bottom of a deep gorge and was flooded four times between 1999 and 2007. Experts advised them to build a £20m concrete wall through the centre of town to keep the water in the river. But this wasn’t allowed as a cost benefit analysis showed that too few people would be protected. But then a local environmentalist explained how the moors had traditionally released rainwater much more slowly, and that centuries ago, monks at nearby Byland Abbey had built a bund (embankment) to hold it back. Eventually academics, the Environment Agency and the Forestry Commission got behind the scheme.

In the streams above the town they built 167 leaky dams of logs and branches which let normal flows through but restrict and slow down high ones. They also used bales of heather to slow the flow in smaller drains and gullies and planted 29 hectares of woodland. They built an embankment, to store floodwater, releasing it slowly through a culvert. 

The scheme appears to be working well.  The total cost was around £2m, a 10th that of the proposed wall. It may not cope with future massive storms, but it is a good first defence.

Currently the moors around Sheffield are managed for grouse shooting. They are burnt and drained to maintain the heather, the ideal habitat for grouse, who are then shot for sport. Instead we should be managing the landscape to maximise flood prevention, carbon absorption and biodiversity. Flood prevention should be considered before flood defences (though these may be needed too). The need for flood prevention should trump landowner’s requirement for shooting profits.

Graham Wroe

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