Thursday 24 May 2018

It's a mistake to ignore natural defences that are better for the land and more cost effective

More dredging is a false solution. Photo: PA
More dredging is a false solution. Photo: PA

Anja Murray

Flooding has caused a lot of suffering in recent years, but responding to the problem by dredging rivers is the wrong approach. We need to be tackling this problem at a landscape scale.

Experience elsewhere has shown that natural flood management can be significantly cheaper, and have far-reaching benefits for the natural environment.

Profound changes in land-use since the 1960s have generally sped up the flow of water through each river catchment. We have obliterated peat bogs and drained away wetlands. In doing so, we have removed the physical infrastructure that would otherwise hold back flood waters.

Add to this the loss of permeability in the land as we have paved over urban areas and compacted soils with intensive farming. Replacing woodlands, wet meadows and marshland with intensively managed ryegrass fields speeds up the flow of water through each catchment.

Instead of allowing rivers to spill over on to floodplains during times of heavy rainfall, floodplains have been drained and 'reclaimed' to increase farm productivity or to accommodate shopping complexes and new housing developments.

And so it is that the landscape of 2017 has little capacity to attenuate flooding. With climate change, extreme flood events are likely to occur once every 10 years by the second half of this century. The wise response would be to reinstate landscape features, like wetlands and woodlands, to help slow the flow and reduce flood risk.

Protecting floodplains from development, and restoring them to a state where they can retain excess water, would do much to alleviate flooding. These are measures that would make our landscapes resilient to the impacts of a warmer and wetter climate.

Natural flood management is about taking a whole catchment approach to managing flood waters, through managing soil, wetlands, woodlands and floodplains to retain water strategically at times of flood risk. This approach has gained recognition in many countries as a viable and cost-effective approach to flood risk, with extensive projects across Europe and further afield that have restored peat bogs, planted riparian woodlands, restored and created new wetlands, and re-profiled rivers and their floodplains to hold back flood waters.

Instead we in Ireland are responding with more dredging. Because dredging reduces local flooding, it is associated with more ubiquitous flood alleviation.

But dredging increases the volume of water that passes through a river channel at any given time, and often exacerbates downstream flooding.

Flood Defence Works Interactive Map

This tool sets out the cost of installing flood defences, the damages which might arise and number of properties under threat, in the most at-risk areas across the State.

It is based on data from the draft Flood Risk Management Plans, produced by the Office of Public Works (OPW), following extensive surveys of 90 coastal communities, and more than 6,500kms of river channel.

The country is divided into 29 Units of Management (UoMs), which are areas covered by a single river basin or covered by a group of smaller rivers. Given its size, works required along the Shannon are set out in three UoM.

Clicking on the icons show the works required in each area.

The urban area is highlighted at the top, and the UoM beneath. The cost of proposed works is set out in €m. The ‘damage uncapped’ figure relates to the total cost of damages to properties and infrastructure which would arise if nothing was done.

The ‘damage’ figure is based on the value of the properties at risk. This figure is used to determine if a scheme should go ahead – if the cost of the damage is less than the cost of providing defences, the scheme may not go ahead. This is the cost-benefit ratio. If it’s less than one, the scheme doesn’t make financial sense.

The final figure is the number of properties protected.

Some icons contain less information. For example, Tullig in Kerry is part of the Castleisland flood defence scheme so no information is contained. The OPW has also identified other areas as being at low risk, or says the existing flood defence regime should be maintained. In other cases it notes the need for a forecasting system, or says if a scheme is underway.

Further information is at

The purpose of dredging was never for flood relief but for the improvement of agricultural land. Yet more flooding in recent years has meant that politicians and local authorities are put under more pressure to allocate public money for more dredging. This can increase vulnerability in flood prone areas.

The Shannon Flood Risk Group, led by the OPW, appears to be entirely focused on dredging: what is being called 'river channel maintenance'. But more dredging is a false solution.

It is understandable more people are getting more insistent we act now to reduce flood risk. And so we must. But leaving landscape-scale solutions out of the picture is folly. We cannot continue to ignore natural flood-management options.

These are cost-effective, long-term approaches that have enormous benefits for water quality and for nature.

The sooner we accept nature is a key, cost-effective ally in the fight against climate change, the sooner we will start to implement sustainable, long-term solutions to the growing problem of flooding.

Anja Murray is a broadcaster and environmentalist

Irish Independent

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