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Flood management: making more of less

As the cuts to flood management budgets bite, David Keiller, technical director, Black & Veatch Europe, Middle East, India & Africa, says public engagement and focussing spend on highest value assets are two ways to stretch funds

In an age of austerity, when public funding for flood defences is being stretched as far as possible, are there ways of cutting expenditure and providing a more sustainable future? The answer is - yes, in the right circumstances.

Flood defences need regular maintenance and occasional major investment to ensure their effectiveness. For earth embankments, this is especially important: the grass needs to be cut to develop a good sward (upper soil layer) and control growth of shrubs and trees.

Banks need to be inspected and damage by cattle trampling down the crest or animals burrowing into the bank needs to be repaired. Erosion protection needs to be checked and kept in good repair. Concrete and steel defences require less frequent maintenance, but repair and replacement when eventually needed is usually more expensive.

Neglect

When maintenance is withdrawn by a public authority all these activities stop; banks are allowed to become overgrown and when damage occurs through storm, corrosion, accident or vandalism it is not repaired. When a defence breaches it is left unrepaired.

This policy allows nature to take its course, and can provide environmental benefits. Alternatively, withdrawal of public maintenance can spur on those who benefit from the defence to take responsibility for its upkeep.

Withdrawal of funding from low-value defences allows the available public funds to be concentrated on maintaining and enhancing the higher value defences that better protect communities and important national assets. Withdrawing public funding from a flood defence is rarely going to be popular with those who benefit from the defences.

They expect ‘the government’ to continue to support them in the manner they have become accustomed to. However, most people grumble about the high level of taxes they pay to support activities they consider less deserving.  

Responsibility

The transfer of responsibility for maintenance of any flood defence from public to private funding must be handled sensitively. Local landowners and the communities they belong to need time and help to adjust to their changed circumstances.

Initially those affected are often angry, but eventually can usually be persuaded to start thinking constructively about how best to take responsibility for maintaining the defences. Withdrawal of maintenance can also have positive impacts on flood risk.

In the River Roding that drains parts of east London and Essex in England, Black & Veatch has developed a strategy to reduce expenditure, reduce flood magnitude, improve flood protection and contribute to improving biodiversity. This work received the Environment Agency Project Excellence Award for Asset Management in 2013.

Withdrawing public funding from flood defences is never a popular policy, nor is it a no-cost option, as it requires significant engagement with communities. Heavy demands of patience, perseverance and an understanding of the consequences for local communities are made on those required to implement this policy.

This task can be made a little easier if communities understand their flood risk and the actions they can take themselves to minimise this risk. Community education plays an ongoing vital part of a sustainable flood risk management policy. 

Withdrawal of maintenance is an important tool in the armoury of a public body trying, with limited funds, to obtain the maximum benefit for society as a whole from its investment in flood defence. In a century when climate change is expected to increase flood risk, rationalising expenditure to concentrate on the most valuable assets is likely to become increasingly important. 

Case study 1: Isle of Axholme

The 376km2 Isle of Axholme pump-drained catchment, alongside the River Trent in Nottinghamshire, offered opportunities to minimise maintenance costs by understanding how maintenance affects flood risk. The catchment has 57 pumping stations of various sizes and more than 90km of embankments, which cost more than £1M per annum to maintain.

Black & Veatch identified that there was an economic case to maintain the defences that prevent the River Trent flooding the land; and also to maintain the two principal land drainage pump stations and drainage routes.

Analysis found there were significant communities in the catchment that would be flooded permanently if this was not done. However, the benefits from managing the second and third tier drainage system, embankments and pump stations, were almost exclusively experienced by the local farming community, who relied on the drainage system to improve their farm incomes.

In this case these beneficiaries either individually or through the local Internal Drainage Boards were best-placed to decide the correct balance between drainage efficiency and the cost of maintaining the system, following the ‘beneficiary pays’ principle.

Case study 2: River Roding catchment

The upper catchment of the River Roding is a very rural area in the London Green Belt, where there is very little property or other development. If maintenance in this part of the channel is stopped, reeds and water vegetation will grow, trees will fall into the river and the flow of water will generally be slowed.

In time of flood, this will slow the run-off of rain from the catchment and so reduce flood peaks in the river further downstream where it passes through the suburbs of London. As the river passes through east London, the reduced flood flows improve the standard of protection and there are more biodiversity gains to be had by reducing maintenance.

Fortunately, despite the expansion of London through the last century, the flood plain of the River Roding has remained largely intact. This allows maintenance of some parts of the channel to be stopped, particularly in areas where the river has been over zealously canalised in the past to minimise flood risks.

Modelling

Modelling showed that if these channels are allowed to develop naturally, without maintenance, there could be a reduction in flood risk to the surrounding properties because of the reduced flood run-off from the upper catchment. Of course the flood plain must be retained and all the bridges across it maintained to ensure there is a clear route for floodwaters down the river valley to where it joins the Thames.

The Roding strategy is expected to reduce flood risk to over 900 properties and show a whole life cost saving of £40M. Although there are good efficiency and biodiversity gains through reduced maintenance, effects on the local community too need to be understood.

In the Roding catchment, some properties will experience increased flood risk as a result of the new policy. The reasons for the change in maintenance spending and the possible effect on individual flood risk have been explained to all those affected.

Guidance and support is being provided to help them make their own arrangements for flood protection.

Topic: Flooding & Urban Drainage , Sewer Networks
Tags: government , banks , funding , soil , trees , policy , maintenance , corrosion , flood defences

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