Managing surface water at the building scale. Dr Susanne Charlesworth, Reader, Urban Physical Geography, Leader:

Transcription

1 Managing surface water at the building scale Dr Susanne Charlesworth, Reader, Urban Physical Geography, Leader:

2 1. Surface water: pluvial or rainwater, not fluvial or river water 2. Has to be managed sustainably: Sustainable Drainage or SUDS 3. What are SUDS? 4. How do SUDS work? 5. Small scale SUDS. 6. Integrating SUDS into cities at the building scale: new build and retrofit

3 Why SUDS now? Water UK s Review Group on Flooding: Lessons Learned from Summer Floods 2007: Bigger pipes are not the solution to bigger storms. The water industry can build extra resilience into the sewer network at a cost but sewers and drains are not flood defences. There will be occasions when the network will not be able to deal with the volumes of water associated with extreme floods. Looking forward, new designs need to consider overland flow routes, sustainable drainage and sacrificial areas for flooding as an alternative to piped sewerage systems for the disposal of surface water. Change in Permitted Development Rights, 2008, paving front gardens: Future Water. Flood and Water Management Act, 2010

4 Context: FWMA Schedule 3 the use of SUDS to manage surface water across England and Wales is encouraged in new build and redevelopments. Requires drainage systems approved against a set of National Standards SUDS Approving Body (SAB) before construction is allowed to begin. Connection to the foul sewer is unchanged Automatic right of connection to a storm sewer has ceased. Through SABs, Local Authorities have responsibility to adopt and maintain

5 Drainage hierarchy Excess water should be discharged into the ground Or it can be discharged to a surface water body If neither of 1 or 2 above are suitable, then planning permission will have to be sought for discharge to a surface water sewer In the event that scenarios 1-3 are not possible, then discharge to a combined sewer will have to be considered. (Defra, 2011)

6 The purpose of SUDS To replicate the natural drainage from a site before it was developed: Greenfield runoff To reduce runoff by integrating storm water controls throughout a site in discrete units or as a train To manage the environmental risks that result from urban runoff To enhance the environment SUDS consider water quantity, quality and amenity value ( 2007 ) al. equally Woods Ballard et Differ from the traditional systems: encourage infiltration and detention It is a way of thinking, a philosophy

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8 SUDs devices at the building scale Swales Green roofs/ walls Porous paving Rainwater harvesting Rain gardens Bioretention Above/ below ground New build/ retrofit Vegetated Hard

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10 Integrating SUDS into the built environment New build vs retrofit?

11 Water Efficient Buildings

12 Integrating SUDS into the built environment: retrofit 70% of homes required by 2040 already exist. What legislation encourages retrofit? Perceived as difficult and expensive Car parks: replace using porous materials, install infiltration devices Green roofs and walls Trees Rainwater harvesting

13 EA (2007): Cost-benefit of SUDS retrofit in urban areas Re permeable paving - has both: net financial benefits for property owners as well as overall net economic benefits. Furthermore: PPS costs less on a lifecycle basis than traditional surfaces Due to ease of replacing block pavers Financial benefits as surface water has to be disposed of on site not by Water Company.

14 Retrofit examples Lambeth Ethelred Estate Sedum roof over 4000m² Biodiversity benefits Car Park before and after installation of porous surface (source: SNIFFER 2006)

15 Worcestershire County Council Waseley Hills School (Robert Bray Associates)

16 Retrofitting green roofs

17 Retrofit: Spain b) Xàtiva Gozalbes Vera Public School 1. Extensive green roof 3. Replacement of sand play area with porous concrete 2. Rainwater tank

18 Benefits Green roof delays runoff by about 30 minutes 50% reduction both in peak flow and runoff total volume. Porous concrete: calculations indicate peak flow reduction of around 70% for the rainfall design event (T=15 years). Calculated that the green roof could sequester about 180 kgc. A school so educates pupils re SUDS

19 Multiple benefits of Green Roofs Roof space up to 50% of impermeable area of a city Mitigation of urban heat island effect Absorption of air pollutants and dust Protect the building fabric from sunlight and temperature variation Noise! Reduce costs, including drainage, heating, air conditioning Reduced energy demands and lengthens life of roof membrane

20 Summary Easy to design in for new build. Relatively easy to retrofit at the small, individual building scale Attenuates the flood peak, has water quality benefits and some amenity/ biodiversity benefits depending on device. Has both financial benefits for the householder as well as wider economic benefits SUDS as an approach is flexible, multiple-benefit beyond simply the SUDS triangle. Must be designed and maintained properly. Many cities have embraced the technology: London, Tokyo, Stuttgart, Chicago etc etc etc.

21 Recommendations Education Use open space such as parks, grass verges, pocket parks More green space daylight streams, more open water Take risks! Detention pond, Dunfermline Eastern Expansion (DEX), Scotland Make more imaginative use of road traffic islands