Foto: Lamb Drove Demonstrating SuDs with Permeable paving, Interpave, https://www.paving.org.uk
The Cambridgeshire Country Council in the UK has learnt that opportunities exist for installs Sustainable Urban Drainage Systems (SUDS), even in small developments. The Cambridge Housing Society developed small-scale affordable housing in Cambourne, with 35 homes in a 1-hectare site.
Flood risk is high in the low-lying area, which suffers from combined flooding events including river floods, flash floods and surface water, alongside storm surge. Climate change is expected to increase the variability and severity of flooding into the future therefore it is important that areas at risk have adequate flood protection measures.
In Cambourne, the developers chose to design a sustainable drainage system, and whilst this has improved flood protection in the area, it has also led to improved water quality, more space for animals and plants, as well as cost savings for the residents and developers as they are not required to pay charges for storm water drainage.
The Adaptation Journey
The positive impact
There was growing pressure for new housing in the UK, and Cambridgeshire is a key growth area under the government’s housing strategy, with up to 50,000 new houses planned to be built by 2016. However, due to the geography of the area and expected climate change impacts into the future, it is important that effective drainage systems are in place to reduce the risk of floods. To address this the developers installed a comprehensive SUDS system with the approval of residents. The system was designed and installed over a period of two-years, and included permeable paving, detention basins, swales, a green roof demo and water butts. To select the measures, the developers identified the sources and routes of flooding risk, which ensured the measures were able to address extreme rainfall impacts in the right places. By implementing SUDS, the project protects the area from the impacts of high rainfall events, as well as providing natural space for wildlife to thrive, and leaving the water quality higher than it would have been under a conventional regime.
How does it work?
After identifying the flood risk areas, the key measures were chosen and then monitored over a two-year period for their performance to be evaluated. The results were then compared with a site that had traditional drainage. The measures chosen can be implemented on both private and publicly owned buildings.
These can be installed in parking areas, drive ways and even roads. There are a variety of materials that can be used, whereby permeable block paving is the most common, and they work by allowing water to soak through the surface to then be held in a gravel material below. This slows down the speed of water moving along the surface, as well as passing into other parts of the drainage system, thereby controlling water flow. The process also helps to improve water quality by removing pollution.
Greening roofs involves installing a thin layer of soil material, which is then planted with specific plants that fit the local biodiversity requirements. These are very effective within SUDS systems as they reduce the amount of water running off of the roofs during heavy rainfall. This reduces the amount of water that needs to then be stored in the ground.
Water butts, swales and detention basins
Water butts are rainwater harvesting tanks that collect rainwater. This can then be used to provide a water supply for outside taps, to water gardens or they can be installed for re-using water to flush toilets. Similar to the other features, collecting the rainwater reduces the volume that needs to be managed via the drainage system. Swales are ditches that are built in gardens to direct and slow the flow of rainwater which runs of roofs during heavy rainfall. This gives the rain a chance to soak into the soil, and flows the water flow. Similarly, detention basins are larger ponds that have dug to hold rainwater runoff and release it slowly over time.
The UK Water Framework Directive had a target of ‘good’ quality ground and surface water by 2015, which this helped to drive the decision to choose a SUDS. The project was also supported by the collaboration of a number of institutions as follows: Cambridge Housing Society, Cambridgeshire County Council, South Cambridgeshire District Council, Flagship, Cambridgeshire Wildlife Trust, Royal Haskoning, Defra, EA, Cambridgeshire Horizons, RSHydro and Robert Bray Associates. Through the project it was learnt that depending upon on the scale of a development or installation, specialist advice is often important.
Obstacles and challenges
The project found that to address the need for accommodating the softer, landscaped SUDS within the housing development, using public open spaces was a viable solution. This included adjacent, off-site spaces to the housing development.
Revitalization of water elements Urban greenery Flood control measures Biodiversity Floods and torrential rainfall Lack of water and drought