New Approaches to Flood Prevention

 

New Approaches to Flood Prevention
Cathal O’Meara MILI, Landscape Architect

Adaptive responses to our changing climate are emerging throughout the world. Rising urban populations and increasing pressure on our natural environment are demanding more creative approaches to out settlement patterns.

In much of the world these pressures are requiring new approaches to urban heat islands, drought, extremes of temperature and rising water levels. In Ireland our dominant natural characteristic is the greenness of our land, which is fed by the persistence of our rainfall. A legacy of opportunistic development, not just in recent years but throughout our history has left us with urban populations on vulnerable floodplains.

Our history with our watercourses is a fraught one. We have constantly sought to shape our water for infrastructural purposes. Our canals for transport, our callows for agriculture, and our valleys for energy. In urban areas this mechanistic view dominated to such an extent that our rivers became giant open sewers, useful for “getting rid” of our waste”.

This technical view dominates to such an extent that current thinking on flood prevention still seeks to “get rid of” excess rainfall as fast as possible. This approach ensures further problems downstream due to increased river flow, meaning greater flooding. Brought into our towns this approach necessarily manifests itself as tall massed concrete straightjackets replacing open views of the water.

This approach requires continuous maintenance, as in anticipation of flooding private contractors have to erect extra steel defences on top of the massed concrete walls. These additional structures continually have to be stored, mounted and dismounted with on-going costs.

This attitude needs to change. Sewage treatment plants have ensured that most of our beaches and rivers are again safe for swimming. Promising projects worldwide are demonstrating the union of ecology, flood prevention and recreation. For over 20 years Curitiba a poor Brazilian City has been using Federal flood prevention money to buy land adjacent to its River. With this land Curitiba has been creating sacrificial Flood/Attenuation parks. Now when flooding occurs the water in the lakes rises but prevents the flooding from damaging the city.

“Room for the River” is a Dutch government plan that seeks to mitigate flooding in the Rhine, the Waal, the Meuse and the Ijsel and spans the countries upstream of these rivers including Switzerland, France and Germany. This plan seeks to do exactly the opposite of what we are currently implementing in Ireland with a suite of measures including depoldering, removing dykes and creating flood channels. By making room for the river the plan allows flooding to happen in designated areas, and by appropriately planting and recreating these wetland landscapes flood attenuation is maximised. This plan aims to slow the rate of flow of rivers and prevent flooding from reaching the towns downstream.

We need to understand flood prevention in a spatial or landscape context as it is the treatment of the land within the wider landscape that affects the likelihood of flooding. This is due to the fact that the amount of water within a river catchment is far in excess of the amount within the river. Currently it appears our policy for flood prevention views towns on the same river catchment as separate projects when clearly they are not. We need a policy approach that takes this into account. The current one-dimensional engineering approach increases the costs and limits the benefits.

flood

 

 

 

 

 

 

 

 

 

 

 

 

 

The view of the Blackwater currently being removed from much of Fermoy Co. Cork under flood prevention works.

To reinterpret the brief with the goals of increased biodiversity, improved recreation while delivering on urban flood prevention would see semi natural biological/engineering solutions replace hard hydraulic engineering.

In effect this could mean making room for the river by recreating callows, wetlands, marshes, flood channels and alluvia carr woodlands on low lying agricultural land.

We could go further and reforest the river’s catchment hills too. Such measures would enhance the capacity of the river catchment for retaining heavy rainfall. Recent studies undertaken in Wales by the Centre for Ecology and Hydrology suggest that water sinks into the soil under trees at 67 times the rate it does under grass. This does not negate the possibility for agriculture. A recent scheme undertaken in the Severn Valley demonstrates that if 5% of farmers in the catchment undertook reforestation, flooding peaks downstream would be reduced by some 29%.

Such living landscapes that retain water have a significantly increased capacity for mitigating flooding, but the benefits of such an approach go further.In a predominantly rural landscape applying solutions that affect farmland is a far more economical means of targeting flood prevention than dealing with the expense and complexity of moving services, negotiating temporary traffic solutions, buying expensive urban land or pile driving along sensitive river banks in built up areas.

However such a proposal could be expanded in recreational terms. By connecting the towns along a watercourse with a network of high quality walking and cycling paths, campsites and linear alluvial forests we could realise the full aesthetic and recreational potential of our watercourses. These could also be the driver of a resilient local economy as the recent creation of the Greenway in Mayo has established.

Solutions for reshaping our watercourses as engineering feats belong to a different era. We need to awaken to the multi-functionality of our rivers as places for us all, flora, fauna and people.

Cathal O’Meara is an Irish Landscape Institute registered Landscape Architect and runs the practice www.cathalomeara.com