The Mayor's draft water strategy - london.gov.uk - Greater London ...

More documents

Recommendations

Info

if only used for toilet flushing or garden watering, will require little disinfection. Yet, regular cleaning of the collection area is important to prevent rainwater contamination from bird droppings. Managing surface water runoff 4.8 The increase of heavy rainfall days and the growth in hard surfaces mean the existing surface water drains can no longer cope with the rise in runoff. In turn, this can lead to a greater risk of flooding as surface water drains are overwhelmed. Conventional drainage systems, with pipes and sewers, are designed to take surface water away from streets and buildings as quickly as possible and discharge it into the main sewers and watercourses. Sustainable drainage systems (SUDS) seek to mimic natural drainage, managing more water above-ground, close to the source, in order to reduce the volume and speed of waters flowing into sewers and watercourses after storms, and therefore the risk of flooding. 4.9 More sustainable drainage, such as using porous surfaces to let rainwater to soak into the ground where soil conditions allow, can avoid or reduce the need to construct surface water drains to distant outfalls. At the same time, it can improve the environment through the creation of habitats and the reduction of pollution. Imaginative sustainable drainage schemes can be developed as attractive landscape features, providing habitat for aquatic wildlife and interesting opportunities for local people to enjoy access to nature. Green roofs can provide another mechanism for slowing rainwater discharge. The Mayor’s supplementary planning guidance for sustainable design and construction set the standards for drainage in new developments. Table 4.1 outlines these standards. 4.10 The Code for Sustainable Homes (referred to earlier in paragraph 3.24) also has criteria for the attenuation of surface water run-off. This requires that surface water run-off rates and annual volumes should be no greater after new homes have been built than before. Further requirements apply where rainwater holding facilities or SUDs are used to attenuate run-off into either natural watercourses or surface water drainage systems 62 . 4.11 In the past, householders faced few barriers to increasing the amount of impervious paving around their property. Paving front Table 4.1 Supplementary planning guidance on Sustainable Design and Construction, 2006 Essential Standards Mayor’s Preferred Standards Use sustainable drainage systems (SUDS) measures, wherever practical. Achieve 50% attenuation of the undeveloped site’s surface water run off at peak times Achieve 100% attenuation of the undeveloped site’s surface water run off at peak times 61
62 The Mayor’s draft water strategy gardens was a permitted development right, and therefore could generally be carried out without planning permission. Following consultations in 2007, the government accepted that, given the contribution of hard standing to surface water flood risk, it would restrict householders’ to porous surfaces. Planning permission is now required for impermeable surfaces in front gardens larger than five square meters 63 . 4.12 The Draft Flood and Water Management Bill will require developers to include sustainable drainage, where practicable, in new developments, built to standards that reduce flood damage and improve water quality 64 . It will also amend section 106 of the Water Industry Act 1991 to make the right to connect surface water run-off to public sewers conditional on meeting the new standards. It will give responsibility for approving sustainable drainage systems in new development, and adopting and maintaining them where they affect more than one property, to a SUDS approving body, generally local authorities. The Mayor supports the legislative changes proposed in the Draft Flood and Water Management Bill in respect of surface water management. Proposal 8 The Mayor will encourage green roofs rainwater harvesting, grey water recycling and sustainable drainage through planning policies in his new London Plan. 4.13 There are instances where surface water drains have been connected to a foul sewer, when connections to separate surface water drains or watercourses were available and would have been more appropriate. This is discussed more fully in paragraphs 5.17 to 5.21. The proposed changes in the right to connect to a public sewer will require effective enforcement by Local Authorities. Risks of flooding 4.14 In London, tidal and fluvial flooding presents a significant risk. About 400,000 properties are at risk from tidal flooding while about 100,000 properties are at risk from fluvial flooding. Also at risk are the Underground system, power supplies, telecommunications and much other critical infrastructure. The Thames Barrier and associated defences protect those properties at risk of tidal flooding to a very high standard so that there is less than a 0.1 per cent chance of flooding in any one year. Those at risk from fluvial flooding are protected to only a moderate standard, typically there is between a one and five per cent chance of flooding in any one year. The flood risk from tidal flooding is therefore very low in probability, but very high in consequence and for fluvial flooding there is a moderate to high probability, but with lower consequences. 4.15 Flooding can have a significant effect on people’s health and wellbeing. As well as physical problems, such as colds and chest infections, flooding can cause increased levels of stress and anxiety, for example, as a result of having to live in temporary accommodation, paying for repairs and dealing with insurers 65 .
Page 1 and 2:
August 2009 The Mayor’s draft wat
Page 3 and 4:
2 The Mayor’s draft water strateg
Page 5 and 6:
5 Disposal of wastewater in London
Page 7 and 8:
Page 9 and 10:
Page 11 and 12: 10 The Mayor’s draft water strate
Page 61: 60 The Mayor’s draft water strate
Page 71 and 72: 70 Figure 5.1 The London sewer syst
Page 73 and 74: 72 periods the sewers quickly fill
Page 99: 98 The Mayor’s draft water strate
show all

The Mayor's draft water strategy - london.gov.uk - Greater London ...

Create successful ePaper yourself

Delete template?

Save as template?