Flood management

13th January 2012

‘Natural disaster’ is a term not usually associated with the UK. Here property, particularly agricultural property, implies stability; if you buy land on Monday you can walk across it on Friday confident it will be in a similar condition, retaining function and value for the future. Land, as agents will remind you, is the safe bet.

So what would you do if there was a likelihood of your most versatile land becoming a useless liability? This was the scenario at the Lanton Estate in north Northumberland, where the River Glen flows through a mixture of arable and livestock farming land.

Flood Risk –the Agricultural Perspective
The Glen is a ‘flashy’ river, with rain in the Cheviots transforming it into a large, destructive flow. The 2008 floods affected many farmers in the catchment and whilst Lanton’s flood defences saved it from serious flooding, a neighbouring estate was less fortunate. Floodwaters breached the defences and the river poured onto arable fields behind, scouring land and depositing tons of gravel. Topsoil was washed downstream with established crops and the land was left uncultivable.

This breach relieved pressure on Lanton’s floodbanks, preventing similar consequences. However the flood defences were severely eroded. Further floods damaged the defences so that by 2010 breaches were appearing – the prospect of versatile land becoming useless gravel fields appeared very real.

Third Party Considerations
From a manager’s perspective this was the worst-case scenario, so why not simply jump in and get on with shoring up the floodbanks?

The Glen is a SSSI, meaning works in the river are strictly controlled by Natural England. One reason for this designation is the river’s importance to migratory salmon, limiting the working window to those months where migration would not be disturbed.

As well as needing to liaise with Natural England, most works to a riverbank or flood defences must be agreed with the Environment Agency, who must be satisfied you will carry out remediation in a competent, effective manner.

The job as agent was to reconcile any potentially competing objectives of the landowner and other interested parties, enabling a solution that was:

a) Cost-effective
b) Legal
c) Capable of standing the test of time
d) Able to be implemented quickly

Implementing a Solution
Several solutions to this problem had been adopted locally.

1.’Hard engineering’, used historically at Lanton. This comprised of stone gabions in front of an earth floodbank. This was discounted because, as well as being expensive, stone gabions were currently part of the problem. Undercut by river water, the baskets were collapsing, undermining the bank they should have protected.

2.Another solution was to breach the floodbanks allowing the land to flood as part of an HLS agreement, whereby payment would be made in return for delivering flood storage or habitat creation. This was also discounted – it was felt to relinquish the productive capacity of the land in return for an income only guaranteed in the short term would have been negligent in this case.

3.The solution selected was to reconstruct the riverbank using a timber palisade. Conifer trunks approximately 3.8m long were driven vertically into the riverbed in two parallel rows, with trunks then laid between them forming a strong wall. Next was to rebuild the floodbank behind the timber. This involved infilling the erosion site with clay, compacted to provide a solid barrier which could then be planted with willow to consolidate the defences into something stronger than could ever be effected with a JCB.

So was it worth it?
Such works are not cheap – at the time of the works timber was about £50/ton and a man and machine cost around £45/hour making tight project management and budgeting important. However one must consider the cost of not doing the work.

The land protected was worth perhaps £6,000/acre. Undefended this land would be frequently flooded, unsuitable for arable cultivations. The most sensible use for such land would be pasture which, given the likelihood of despoiling with gravel, would probably not have been worth half this sum.

Considered against the land protected, the cost of the work was approximately £150 per acre. This delivered a solution which will strengthen through time as growing willow consolidates the work.

Lessons
The reinstatement described has now been used on four locations at Lanton, either as emergency works or running maintenance.

People have sometimes said ‘time was when the EA would have done this for you’; well in this brave new world it is unlikely a governmental fairy godmother is going to come forward to save the day.

Whilst flood risk management may seem an uphill struggle, through pro-active, defensive maintenance farmers with ageing flood defences are able to protect their property in a way that is cost-effective and acceptable to regulators, preserving their asset for the future.

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