It never rains but it pours!

By: 
Janet Moxley
on : 
13th Jan 2016
Bulletin item expiry date: 
12th Feb 2016

 

In case you haven’t noticed it’s been pretty wet across the UK this winter. As a kayaker I usually like a bit more rain than most, but when people are being flooded out of their homes and infrastructure seriously damaged it stops being fun!
Unlike in England and Wales in Scotland we have generally been pretty good at not building on flood plains – places that are flooding like Hawick town centre and houses close to Tweed Green in Peebles  are long established, so what’s changed?

It might seem obvious that the main cause of the floods is that a lot of water fell out of the sky. Record amounts of rainfall fell in very short periods. This is bound to cause floods somewhere. However, the record rainfall is driven by climate change, and even with the amount of change we’re already committed to as a result of greenhouse gas emissions so far we can expect more frequent and more events of heavy rainfall. In winter in Scotland this will probably be made worse by there being more rain and less snow, as snow in the hills generally (but not always) melts gradually over several days or weeks rather than hitting river systems all at once.

If we don’t address climate change no amount of flood defences will help. To reduce flood risk in the long term we must take decisive action to reduce out greenhouse gas emissions. In the shorter term we are committed to a changing climate, and climate models give us a good idea what changes we can expect in the UK. Although we know what changes are likely we have neither done enough to reduce greenhouse gas emissions nor done enough to adapt to the consequences. There is consensus amongst hydrologists and planner on what needs to be done, but we have been very timid about actually doing anything.
Historically flood defence has involved building barricades to protect property and trying to skoosh water down stream as fast possible, but this imply shifts the problem. Building more barriers and focussing on pushing water downstream is likely to cause more problems than it solves as well as being very expensive.

There are a number of ways in which catchment management can help reduce the flood risk after heavy rainfall. Catchment management may not be the root cause of flooding, but it can certainly reduce the impacts.
In the last couple of centuries land management, particularly on agricultural land has become more and more intensive. This management has been carried out with the understandable aim of increasing agricultural production, but in some cases has had profound effects on how water flows through catchments. Every farmer has been keen to get water off their land as quickly as possible. Field drains have moved water off fields into ditches which flow into rivers. Water meadows which hold back water have been drained, and river channels straightened out to make regular shaped fields.Until the introduction of the EU Water Framework Directive in 2000 there were no controls on diverting rivers or activities such as dredging which moved water downstream. Since 2000 these activities have been regulated by SEPA and the Environment Agency much to the annoyance of the Daily Mail and it’s team of vocal but untrained amateur hydrological pundits.
In the Tweed catchment, the Biggar Burn between Biggar and Broughton was completely straightened in the early 1900s partly to “improve” farmland by draining and ploughing and partly to allow the now dismantled railway track to follow a straight course without having to construct lots of bridges.
Disused railway line running straight through the Biggar Burn's flood plain.
Disused railway line running straight through the Biggar Burn’s flood plain.

Mill towns such as Hawick grew up around rivers which provided the power for the machinery. In some cases catchments were altered so that water was diverted increase floods through the mill lades, which may not longer exist as the mills have turned to other power sources or closed altogether. In mill towns river courses have been diverted between the buildings so that water can only go up not out. Bridges and other structures in rivers can lead to water backing up behind them. It may not be possible to move town centres away from rivers in towns like this or to remove all structures in rivers but planning the management of areas upstream can reduce flood risk.

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Teviot, Hawick Town Centre, Dec 2015.

As well as changes which directly affect the rivers and burn, other changes in the way in which land is managed can affect how fast water runs through catchments and into streams and rivers.
One of these is loss of trees. Trees are pumps. They move water from the ground to the atmosphere through evapotranspiration. Conifers do this all year. Broadleafs only in summer. Trees also slow down rainfall – water drips slowly through the canopy rather than pouring onto bare ground. Many hedges with associated trees have been replaced by barbed wire, and coppices and small farm woodlands have been removed.

Right at the top of catchments heather management can also affect run-off. Heather burning reduces removes water retaining peat soils, makes the remaining soil more water-repellent and less able to hold water the height of heather

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Muirburn can affect the hydrology of upland catchments

Lower down improved grassland has been ploughed, seeded and rolled. This lands the land nice and flat which prevents puddling which reduces grass yields, but it also makes water runs faster. Semi-natural grassland is hummock and retains water in the hollows. Compare water flow down a piece of smooth card to that down corrugated card. If soil on agricultural land becomes compacted  due to trampling or heavy vehicles this can further increase run-off.

Improved pasture can increase run-off compared to more natural grassland.
Improved pasture can increase run-off compared to more natural grassland.

In built up areas land has been increasingly covered in concrete. Roads, driveways, houses etc all skoosh water off the land into rivers, yet there seems to be no will to reduce road building or even introduce planning controls to prevent urban greenspace such as parks and gardens being concreted over.
So what will help? Firstly we urgently need to reduce greenhouse gas emissions. Without that we will be firefighting to control ever-increasing peak rainfalls.

Secondly we need to get on and implement plans for adapting to climate change not just talk about them. We have a pretty good idea how climate is changing and we know that warmer, wetter weather with more heavy downpours interspersed by droughts in summer are likely. This means tackling water management throughout catchments, not just focussing on building higher and higher flood defences. Anyone who has ever tried to keep sandcastle safe from a rising tide will know that the water wins in the end!
Instead of flood defence we need better flood control. Flood defences are expensive and may be necessary where irreversible changes have increased flood risk, but flood control measure could be relative cheap and bring other benefits was well. However this will mean working with land owners in catchments and probably compensating them for reversing measures they have taken to “improve” their land.
Many of these catchment management measures have other benefits as well as reducing flood risk. For example planting hedges and farm woodlands (particularly native broadleaf trees), reducing the area of monoculture heather moorland and allowing some “improved” grassland to revert to a semi-natural state would increase biodiversity.
Where river channels have been straightened more natural meandering paths should be re-instated to store more water in the river channels. This could also benefit anglers by allowing a more natural river system of shingle banks and pools to develop. Areas which could act as “sacrificial” flooding areas upstream of flood-prone settlements should be identified and flood control measures built to restrict flood and allow water to flood these areas instead of towns. This isn’t just pie in the sky. Where it’s been trialled, for example on the Eddleston Water which flows into the Tweed in Peebles and Pickering in Yorkshire it’s been shown to work.
Dredging, straightening and culverting of water courses should be banned in all but the most exceptional circumstances, and where possible existing straightening and culverting should be reversed, with compensation where agricultural production is reduced as a result. Unfortunately some politicians are still trying to play Canute.
Management of heather moorland is well overdue for much more scrutiny, particularly the effects of muirburn, which not only changes soil hydrology and reduced biodiversity but also leads to emissions for greenhouse gases and soot.

Retaining water at the top of river catchments through land management that slows its journey downstream not only helps to reduce flood risk, it can also combat droughts during dry periods, so two problems which climate change is likely to exacerbate are tackled at once.
In contrast to  England and Wales where the Environment Agency is responsible for flood defence SEPA has more limited involvement and only provides flood forecasting,  measurement of river floods, and advice on the flood risk of planning applications. In Scotland councils are responsible for flood defence, but have suffered reduced budgets in real terms as a result of the council tax freeze.
 
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Some bridges can obstruct flow, but there’s plenty of space under Fernilee Bridge on the Tweed,

 
At a time when budgets are tight improved flood prevention will need some money to be spent, however addressing flooding through catchment planning rather than hard flood defences such as barriers may be both cheaper and more effective. The Common Agricultural Policy (CAP) payment regime could be adjusted to compensate land owners for adopting practices which reduce flood risk to property downstream. In particular agri-environment schemes (Pillar 2 payments) could be more targetted on flood prevention. However uptake for Pillar 2 schemes tends to be low, so as well as incentives there may need to be some compulsion or controls. Forest grant schemes could encourage reforestion of catchments where there is a high flood risk. Agricultural activities and changes in land use do not generally require planning consent even when these changes cover large areas, and are likely to have effects beyond the areas owned by the person making the change. Perhaps its time for that to change.
And we need to look beyond to capital costs of flood prevent to the avoided costs which result from not having to deal with flooding emergencies. The cost of people having to clean up their homes, the cost of damage to roads and bridges. The cost to the Scottish economy of the closure of the West Coast mainline for over a month because of damage to Lamington viaduct because of flood damage has not been estimated, but is likely to be high.

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Repairs to Lamington viaduct on the West Coast mainline. Flood damage has closed the line for at least a month.

We need to think tackle floods and we need to do so sustainably. To do so we need to tackle climate change and think about how we manage catchments not just about flood barriers and sandbags.
 
You can read more of Janet's blogs here: biggarideas.wordpress.com/