This spring we have seen a number of extreme local flooding incidents.  I have seen a lot of coverage of the impacts on people struggling to cope or of people banding together to help each other deal with the impacts.  But I haven’t seen much about why the flood happened in the first place, and importantly, following on from that, how to try and avoid it happening again.   There is of course only so much we might do about the rain, but we can do something about the nature of the land it falls upon, where and how it drains, how quickly it runs off and how much damage it does in the process.

Only last week, I watched torrents of water flood down Scone main street.  That week flooding was already front and centre of my mind, after a friend asked me to help advise over a flood event in Cupar that nearly put his company out of business.   He wanted to know what could be done to prevent it happening again.  

In both cases there was a very similar MO.  An extremely heavy rain shower hit high ground, with nowhere to pool, so almost instantly, large quantities of water gathered pace and swept down hill, flooding everything in its path.  However, this issue is not just about water.  It is also about soil.  In both cases the water ran brown – full of soil and sediment and taking half the farmer’s top soil with it, and silting up drains in the process.  In Scone the road works have clearly exposed more soil, and the drainage they have installed is clearly inadequate, but in both cases the farmer had ploughed downhill.  In both cases the crop in the fields was potatoes, some of these even finding their way into properties during the incidents.  In both cases there was significant damage to roads and properties.  And yet in both cases water levels returned to normal within in a few hours.  Unfortunately for those in its wake, the damage had been done by then.  In my friend’s case, perhaps as much as £250,000 of damage!

The intensity of the rain is a factor, but why is it flooding?  This question matters, because without an answer we are helpless to do anything to prevent it happening again.   So, perhaps the question is - why does the water flash off the land so quickly?  And is there anything that can be done to stop it or slow it down?

In essence, for the best part of 200 years, we have invested a great deal of effort in rebuilding our landscape to drain more quickly and to speed up the rate water runs downhill. But more than ever we are seeing the consequences in our streets, homes and the frailty of our infrastructure. 

Even as far back as 1849 a local historian Peacock, wrote about seeing significant increases in water levels in the Tay, as a result of increased agricultural drainage in the upper catchment of the river.  Field drains were being employed to get water out of fields more quickly, to prevent it spoiling the crop.  It improved the yield, but put more pressure on communities downstream.  But since that period we have seen more and more field drainage, and more and more similar actions which accelerate this process further.

For example we have seen projects to ‘straighten’ water courses and rivers and increase ditches and culverts – so speeding up the flow of water significantly.  In addition we have removed from our landscape some of the natural defences we have against flooding – trees, bushes, water features, flood meadows – and made fields bigger too.  Add to this the fact that we have increased the amount and depth of ploughing, which destabilises the soil, especially if we then plant root crops, which are good for breaking up the ground, but exacerbate problems when it rains on a slope.  Potatoes are well understood to be about the worst crop to plant for flooding.  And we continue to plough up and downhill across the contours, not side to side along the contours, so when it does rain on a slope, we have created channels for the water to run down even more quickly. 

If there is soil in flood water, it has probably come from a farm or a building site, and there is a lot more we could do to prevent it leaving the field in the first place.   We need to be able to prevent the water building momentum, to hold it back for longer and to slow it down when it does start to run off.  We should be ploughing across the hillside, and planting something which binds soil better, especially downhill from a crop like potatoes.   It used to be common to plough across the slope at the bottom of a field (an ‘end rigg’), but this has become less common practice.  It might not have stopped it flooding entirely but it might have helped. And topsoil is valuable – it contains most of the nutrients in the soil, so farmers don’t really want to lose it.  If we are serious about preserving topsoil, we should be considering landscaping – building banks, bunds, natural soakaways and buffer strips full of hedging and soil binding plants.  

If done well the land will then drain itself at a more natural pace, and prevent most of the problems we are witnessing. 

The problem with such heavy deposition of soil, is that even if councils keep the drains clear (and I’ve seen plenty of evidence to say this is more patchy than it ideally should be), the silt will overwhelm some drainage and flooding will be directed down streets and other routes – water will always find a way.  Drains need to be kept clean and councils could surely do more, but there is still a danger this simply puts pressure further ‘downstream’, so it still makes sense to prioritise those actions, like field improvements, which will cut it off at source.

There is something else that both of these flood-hit sites shared in common too.  They are both designated for housing developments.   Very large numbers of houses are planned for Scone above the existing village, and for Cupar across the whole of the northern perimeter, again uphill of the existing town.  This might reduce the soil in the run-off because tilled soil will be replaced by concrete and tarmac, but that is small consolation.  It will increase the volume of water running off the hillside even more substantially, because houses, roads and hard standing are even less porous than heavily drained fields, and it will further reduce the land’s ability to soak up excess rain water.   In other words, rainstorms won’t need to be as intense to still cause flooding downhill and down-stream.

This would all be a recipe for problems, but is more urgent than ever, because we are now seeing increasing rain and storm intensities because of climate change.  Climate change is not optional after all – the impacts are already with us, and all the scientific predictions tell us this is going to only get worse.   With one in five households in the UK at risk of flooding, this is a topic we really need to take more seriously before it occurs, not just afterwards, when it is too late.  Adaptation is essential to protect communities, and one possible first step is more sensitive farming practice in prone areas.  Sensitive urban design is vital too, and should be the norm not the exception.  We need to take a more responsible and holistic approach to local land management.  And ultimately we need to cut our greenhouse gas emissions too, because it is not possible to keep adapting forever. 

Flooding is a complex issue, which is usually a result of a combination of factors working together.  However, if there is nowhere for rain water to pool and drain slowly, then it will run off land more quickly.  There are a range of measures that can be taken to slow down flow, avoid the worst impacts and to minimise damage downhill and downstream.  It is vital for almost every existing community in the face of increasing climate change, and every new housing development, that we start to take them seriously.