As the flood waters recede, a plethora of plans are being proposed to minimise the risk of future flooding. These include barriers and other flood defences, dredging, a reappraisal of planning development and a possible relocation programme for those living in flood-prone areas, as proposed by Minister for Public Expenditure Brendan Howlin last Sunday.
Most measures are extremely costly and some, even if carried out, may transfer the problem to other locations.
While flooding is a natural phenomenon, there is little doubt that man has exacerbated the situation through a combination of bad planning and rapid development. Unlike Ireland, most European countries use technology as just one part of the solution. Forests and riparian woodlands are an integral aspect of land protection and management to minimise erosion and flood damage.
This approach is emphasised in publications such as the 2010 EU green paper Preparing forests for climate change and the recent Confor report The role of productive woodlands in water management.
The EU paper states: “Forests play a major role in the storage, purification and release of water to surface water bodies and subsurface aquifers. Their soils buffer large quantities of water, reducing flooding.”
The Confor publication describes the water benefits that can result from investing in the expansion of well-designed, productive woodlands. Edinburgh-based Confor, an umbrella forestry organisation, claims that past negative associations between productive woodlands and water have been addressed in Britain due to effective water guidelines and forestry standards which are also in place in Ireland.
“As a result, planting productive woodland can offer similar, and in some cases greater, benefits to the water environment than non-productive woodlands,” the publication claims.
Productive woodland is defined in government open habitats policy for England as woodland likely to achieve, at least, yield class (YC) 10 (m3/ha/annum) for conifers and YC 6 for broadleaves.
The paper outlines the following four benefits of forests in reducing water flows:
Greater water use of trees reduces the volume of flood water at source.High infiltration rates of woodland soil reduces rapid surface runoff and flood generation.Greater hydraulic roughness exerted by trees, shrubs and large woody debris along stream sides and within floodplains slows down flood flows and enhances flood storage.Ability of trees to protect the soil from erosion and interrupt the delivery of sediment runoff helps to maintain the capacity of river channels to convey flood waters downstream and reduces the need for dredging.Confor maintains that conifers provide the greatest benefits for reducing water flows. They provide larger evaporation or interception of rainwater, which can reduce the volume of rainfall landing on the ground by 25% to 45% on an annual basis, compared with 10% to 25% for broadleaves.
“While broadleaves demonstrate lower water use, the taller and more developed canopies of productive broadleaves, together with their higher growth rates, could be expected to enhance the evaporative loss compared with non-productive woodland.”
The paper also claims that productive forests can be particularly efficient at intercepting and reducing the delivery of diffuse pollutants to water from upslope land.
“For the nutrients nitrate and phosphate, this mainly reflects the strong nutrient demand by the growing trees, which is maintained by regular thinning or harvesting,” Confor maintains.
“Such active management ensures woodland buffers do not become saturated by high nutrient inputs in drainage waters as the trees mature.”
Virtually all the Confor findings are relevant to Ireland.
“Society is increasingly threatened by flooding, while the water environment remains seriously impacted by a range of human pressures, including diffuse water pollution,” the paper maintains.
“There is strong evidence to support woodland creation in appropriate locations to help manage these issues.”
Woodlands and water
The benefits of forestry in relation to flood mitigation and related issues such as water quality are recognised in many European countries.
In France, forests play a key role in flood prevention. The Restauration des Terrains en Montagne (RTM – Restoration of Mountain Lands) was established to protect land after the floods of 1856 and 1859 which resulted in part from deforestation. Today, the law of 1882 still regulates the RTM, with strong emphasis on reforestation.
Purification
Apart from flood mitigation, the water purification role of forests, including that of forest soils is stressed by the EU green paper Preparing forests for climate change. The paper acknowledges that forest canopies “break down or absorb most air pollutants carried by rain”.
As a result, many EU member states make use of the water regulating role of forests in the provision of drinking water.
“In Belgium, water from the Ardennes forest area is the principal supply source for Brussels and Flanders,” the paper maintains.
“In Germany, two thirds of the water protection areas for high-quality water or Wasserschutzgebiete are under forest cover,” according to the paper.
“In Spain, forests in upper river catchments have been given special conservation status because of their capacity to improve water quality.”
Parlon challenged on siltation remarks
As forest are highly regarded internationally in regulating water flows, a number of forestry organisations were surprised and disappointed by comments made by director of the Construction Industry Federation Tom Parlon last Thursday on the contribution of forests to the siltation of the River Shannon.
Speaking on RTÉ’s Today with Sean O’Rourke programme, Mr Parlon said: “When you plant forests, you dig drains through the mountains, you throw up pieces of spoil when you plant the young trees. It means that the water runs off those mountains very quickly and brings some sediment into the Shannon.”
Scientific opinion
Responding to Parlon, Alistair Pfeifer of the Society of Irish Foresters said: “Tom Parlon’s remarks regarding the contribution of forests to the flooding problem experienced in the Shannon catchment are at odds with international scientific opinion.”
He said forests are widely recognised as having a significant part to play in the regulation of the hydrological cycle and are regarded as an important tool in catchment management.
“Forests and woodlands have long been associated with an ability to reduce flood flows compared with other land use, including the ability to reduce the volume of flood water at source, while the higher infiltration rates of woodland soils reduces rapid surface runoff and flood generation,” he said.
“Studies have found infiltration rates to be up to 60 times higher within woodland shelter belts compared with grazed pasture.”
He said that a particular benefit of productive woodland results from the use of ground preparation for planting.
Rainfall infiltration
“Shallow cultivation can be very effective at disrupting surface compaction in grazed pasture or plough pans in cultivated agricultural soils, markedly increasing rainfall infiltration into the soil and thereby reducing rapid surface runoff that would otherwise contribute to flood flows.”
In addition to the natural processes of interception and infiltration, he said “waterways are further protected by the implementation of Forest Service guidelines and forest certification schemes that require water protection measures to be implemented, such as the establishment of buffer zones (5m to 10m), riparian woodland along all waterways and construction of drainage schemes that prevent siltation and slow down water run-off”.
As the flood waters recede, a plethora of plans are being proposed to minimise the risk of future flooding. These include barriers and other flood defences, dredging, a reappraisal of planning development and a possible relocation programme for those living in flood-prone areas, as proposed by Minister for Public Expenditure Brendan Howlin last Sunday.
Most measures are extremely costly and some, even if carried out, may transfer the problem to other locations.
While flooding is a natural phenomenon, there is little doubt that man has exacerbated the situation through a combination of bad planning and rapid development. Unlike Ireland, most European countries use technology as just one part of the solution. Forests and riparian woodlands are an integral aspect of land protection and management to minimise erosion and flood damage.
This approach is emphasised in publications such as the 2010 EU green paper Preparing forests for climate change and the recent Confor report The role of productive woodlands in water management.
The EU paper states: “Forests play a major role in the storage, purification and release of water to surface water bodies and subsurface aquifers. Their soils buffer large quantities of water, reducing flooding.”
The Confor publication describes the water benefits that can result from investing in the expansion of well-designed, productive woodlands. Edinburgh-based Confor, an umbrella forestry organisation, claims that past negative associations between productive woodlands and water have been addressed in Britain due to effective water guidelines and forestry standards which are also in place in Ireland.
“As a result, planting productive woodland can offer similar, and in some cases greater, benefits to the water environment than non-productive woodlands,” the publication claims.
Productive woodland is defined in government open habitats policy for England as woodland likely to achieve, at least, yield class (YC) 10 (m3/ha/annum) for conifers and YC 6 for broadleaves.
The paper outlines the following four benefits of forests in reducing water flows:
Greater water use of trees reduces the volume of flood water at source.High infiltration rates of woodland soil reduces rapid surface runoff and flood generation.Greater hydraulic roughness exerted by trees, shrubs and large woody debris along stream sides and within floodplains slows down flood flows and enhances flood storage.Ability of trees to protect the soil from erosion and interrupt the delivery of sediment runoff helps to maintain the capacity of river channels to convey flood waters downstream and reduces the need for dredging.Confor maintains that conifers provide the greatest benefits for reducing water flows. They provide larger evaporation or interception of rainwater, which can reduce the volume of rainfall landing on the ground by 25% to 45% on an annual basis, compared with 10% to 25% for broadleaves.
“While broadleaves demonstrate lower water use, the taller and more developed canopies of productive broadleaves, together with their higher growth rates, could be expected to enhance the evaporative loss compared with non-productive woodland.”
The paper also claims that productive forests can be particularly efficient at intercepting and reducing the delivery of diffuse pollutants to water from upslope land.
“For the nutrients nitrate and phosphate, this mainly reflects the strong nutrient demand by the growing trees, which is maintained by regular thinning or harvesting,” Confor maintains.
“Such active management ensures woodland buffers do not become saturated by high nutrient inputs in drainage waters as the trees mature.”
Virtually all the Confor findings are relevant to Ireland.
“Society is increasingly threatened by flooding, while the water environment remains seriously impacted by a range of human pressures, including diffuse water pollution,” the paper maintains.
“There is strong evidence to support woodland creation in appropriate locations to help manage these issues.”
Woodlands and water
The benefits of forestry in relation to flood mitigation and related issues such as water quality are recognised in many European countries.
In France, forests play a key role in flood prevention. The Restauration des Terrains en Montagne (RTM – Restoration of Mountain Lands) was established to protect land after the floods of 1856 and 1859 which resulted in part from deforestation. Today, the law of 1882 still regulates the RTM, with strong emphasis on reforestation.
Purification
Apart from flood mitigation, the water purification role of forests, including that of forest soils is stressed by the EU green paper Preparing forests for climate change. The paper acknowledges that forest canopies “break down or absorb most air pollutants carried by rain”.
As a result, many EU member states make use of the water regulating role of forests in the provision of drinking water.
“In Belgium, water from the Ardennes forest area is the principal supply source for Brussels and Flanders,” the paper maintains.
“In Germany, two thirds of the water protection areas for high-quality water or Wasserschutzgebiete are under forest cover,” according to the paper.
“In Spain, forests in upper river catchments have been given special conservation status because of their capacity to improve water quality.”
Parlon challenged on siltation remarks
As forest are highly regarded internationally in regulating water flows, a number of forestry organisations were surprised and disappointed by comments made by director of the Construction Industry Federation Tom Parlon last Thursday on the contribution of forests to the siltation of the River Shannon.
Speaking on RTÉ’s Today with Sean O’Rourke programme, Mr Parlon said: “When you plant forests, you dig drains through the mountains, you throw up pieces of spoil when you plant the young trees. It means that the water runs off those mountains very quickly and brings some sediment into the Shannon.”
Scientific opinion
Responding to Parlon, Alistair Pfeifer of the Society of Irish Foresters said: “Tom Parlon’s remarks regarding the contribution of forests to the flooding problem experienced in the Shannon catchment are at odds with international scientific opinion.”
He said forests are widely recognised as having a significant part to play in the regulation of the hydrological cycle and are regarded as an important tool in catchment management.
“Forests and woodlands have long been associated with an ability to reduce flood flows compared with other land use, including the ability to reduce the volume of flood water at source, while the higher infiltration rates of woodland soils reduces rapid surface runoff and flood generation,” he said.
“Studies have found infiltration rates to be up to 60 times higher within woodland shelter belts compared with grazed pasture.”
He said that a particular benefit of productive woodland results from the use of ground preparation for planting.
Rainfall infiltration
“Shallow cultivation can be very effective at disrupting surface compaction in grazed pasture or plough pans in cultivated agricultural soils, markedly increasing rainfall infiltration into the soil and thereby reducing rapid surface runoff that would otherwise contribute to flood flows.”
In addition to the natural processes of interception and infiltration, he said “waterways are further protected by the implementation of Forest Service guidelines and forest certification schemes that require water protection measures to be implemented, such as the establishment of buffer zones (5m to 10m), riparian woodland along all waterways and construction of drainage schemes that prevent siltation and slow down water run-off”.
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