A new guidance document on constructed wetlands has been launched. Integrated constructed wetlands (ICWs) are natural sewerage systems which are very kind to the environment. They can deal with farmyard soiled water and domestic wastewater applications. They consist of a series of connected ponds, through which the polluted water flows. Nutrient removal is facilitated by the action of specific plants. While more than a hundred native species can be used, in general about 12 species have most commonly been used including sedges, bulrushes and iris.
”ICWs are not simply concerned with wastewater treatment. In addition to this core function, they can support biodiversity and play a role in flood attenuation. These services are provided in a sustainable and cost effective way using local materials and local workers. ICWs are less about the concrete tanks and pumps associated with conventionally engineered waste water treatment plants and more about soft engineering, aquatic plants and landscape-fit,” says John Gormley TD, Minister for the Environment, Heritage and Local Government, who launched the guidance document.
Ireland has lost most of its natural wetlands over centuries of human habitation. In the nineteenth century, coastal wetlands such as Wexford’s North and South Slobs were drained as polders for agricultural purposes. Rivers were deepened and straightened for navigation. New railways and roads were constructed on causeways across wetlands. “ICWs have the potential to begin a modest reversal of these losses and to provide many of the ecosystem services of the lost natural wetlands,” he adds.
Natural wetlands act as a sponge to contain water during times of heavy rainfall and to slowly release it during drier times, thus providing a natural balance. Not surprisingly when land is drained the water from extreme weather events rushes downstream and can cause flooding elsewhere. We have witnessed several such destructive scenes in recent
ICWs can help restore this natural wetland service by containing and slowly releasing water after heavy rainfall, flattening out the peaks and troughs of flow in rivers and streams, to the benefit of aquatic ecosystems and the attenuation of flooding.
The Water Services Investment Programme 2010-2012, which was published earlier this year, highlights the role that ICWs can play in wastewater treatment, especially for smaller locations. The National Rural Water Services Committee is now finalising its recommendations on funding priorities for 2011 which will include waste water treatment schemes for smaller towns and villages. It is envisaged that specific resources may be ring-fenced for ICW development in this context, in 2011.