In an ever increasing urbanised world where permeable surfaces such as vegetated land are being replaced with impermeable surfaces such as concrete, there is an increasing need to ensure that there are efficient drainage systems to cope with the increased surface water run off.
Increased surface run off can lead to flooding, especially in urban areas and because urban areas have very little permeable surfaces wastewater is instantly collected on the surface, leading to flash flooding in extreme cases. As the Environment Agency [1] states, we need to find ways to ensure that water stays on site longer, which helps to prevent it being polluted and also enables us to store it for future use. Figure 1 illustrates the impact of urban development on the runoff pattern of surface water.
Sustainable urban drainage systems (SUDS) work by replicating natural systems to treat and drain dirty water and surface water. SUDS collect, store and clean the wastewater before then releasing it back into the environment. SUDS do not reduce the amount of flooding but what they do do is reduce the impact of potential flooding. The use of reed beds is an example of a sustainable urban drainage system.
Reed Beds
Reed beds can be used for a wide range of wastewater treatment ranging from domestic use to the treatment of farm waste and even the treatment of heavy industrial contaminants. One of the advantages of sustainable urban drainage systems is that they are visually more attractive than other forms of wastewater treatment and this is certainly the case with reed beds. Other advantages of reed beds include:
- Low operational costs
- No operational noise
- No electricity needed
- Do not produce sludge
- Enhance the natural environment
- Provide habitats for invertebrae such as dragonflies
[3]
Reed beds are not a new form of wastewater treatment; they are actually one of the oldest forms of water purification and are now quite commonly used for the treatment of farm waste. The three elements to reed beds are plants, bacteria and water. Reed beds operate by transferring oxygen from the leaves of the reeds down through the plants to the root system. This enables a very high population of microorganism to occur and as the wastewater moves slowly though the reed bed it can be treated. The treatment of the wastewater means that the environment is protected from the discharge of harmful wastewaters and in some cases drinking water has been delivered through the reed bed system.
There are different types of reed bed systems and which one is used depends on the nature of the land that is available. The two main types are vertical or horizontal reed beds and these can be used on flat or sloping land.
The horizontal reed bed system is the most common type and it is constructed of a shallow structure, which is lined and flooded to below the gravel line. The wastewater enters at one end and passes through the bacteria rich reeds before being discharged at the other end. The vertical reed bed is deeper and is constructed of layers of different sized gravel. Wastewater enters the top of the bed in batches, flooding the surface and then draining through. One advantage to vertical beds is that they use less land area.
Sustainable Urban Drainage Systems not only provide a more environmentally friendly method of treating wastewater but they also provide additional green areas, which can provide habitats for animals and aesthetic qualities for people to enjoy. This is especially true in urban areas where they can act as a corridor for the movement of wildlife. A reed pond not only mitigates against the effects of an ever-increasing urbanised environment, but it also adds to the quality of the surrounding area.
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References
[1] The Environment Agency (2010) [Online]. Available from: http://www.environment-agency.gov.uk
[2]Sustainable Urban Drainage Systems (SUDS) an Introduction (2003) [Online} Available from: http://www.environment-agency.gov.uk/static/documents/Leisure/GEHO0308BNSS-e-e.pdf
[3] The Renewable Energy Centre (2010) [Online]. Available from: http://www.therenewableenergycentre.co.uk
