Suds: Breaking down barriers
New planning guidance will mean better landscaping as developers will have to consider sustainable drainage systems. Richard Whale, chair of EIC's Water Pollution Control Working Group, reports
Many of the techniques used in Sustainable Urban Drainage Systems (Suds) are not new, or even new to the UK. But their usage in development has previously been restricted to flood risk management, mainly where the public sewer has insufficient capacity to receive an unrestricted surface water discharge from a development. The Environmental Industries Commission’s (EIC) Water Pollution Control Working Group believes that this is a missed opportunity. And it is currently preparing a position paper identifying legislative and regulatory barriers to the take up of Suds.
Our current understanding of Suds and the benefits they provide in terms of managing flood risk, improving water quality and enhancing bio-diversity is good and constantly being developed. A great deal of our knowledge is disseminated by best-practice organisation Ciria, which has published several manuals promoting Suds use. Despite the obvious benefits, the use of Suds remains largely dependent upon the available capacity of a receiving sewer or watercourse.
Planning Policy Guidance 3: Housing (PPG3) encourages local planning authorities to promote developments that use land efficiently. New housing development in England is currently built at an average of 25 dwellings per hectare. However, more than half is built at densities of less than 20 dwellings per hectare. This represents a level of land take which is historically very high and which can no longer be sustained according to the Department for Communities and Local Government (DCLG).
Consequently, PPG3 directs planners to approve developments that provide housing densities of between 30 and 50 dwellings per hectare.
In reality, achieving such high housing densities would create unsuitable conditions for the use of natural drainage techniques such as detention basins and ponds which require significant land take. Even the use of swales (often considered a relatively compact Suds technique) is often curtailed because of their influence on the width of highway corridors.
An emphasis on flood risk management and maintaining high residential densities has steered drainage engineers towards solutions that have the smallest impact on development footprints. Consequently, below-ground attenuation techniques using oversized pipes or tanks are routinely used, while a site’s natural hydrology is rarely considered in detail during the planning process.
These below-ground attenuation systems provided are often submitted to the local sewerage company for adoption. Their adoption is made possible in law as they may be defined as sewers. The adoption process is also assisted by hydraulic design software from which the adequacy of the design is easily verified. This is not always possible with Suds techniques where often there is insufficient hydrological information to demonstrate seasonable variations and hence system acceptability.
Contrary to popular belief, it is possible to reconcile Suds use with PPG3. PPG3 does recognise the importance of green open spaces in enhancing the quality of development and assisting with the permeability of land for storm drainage and supporting bio-diversity. Landscaping should be an integral part of new development and opportunities should be taken for the retention of existing trees and shrubs and for new plantings incorporating swales, basins and other sustainable drainage features.
Furthermore, local planning authorities should have clear policies for incorporating sufficient green open spaces into new housing developments. PPG17: Sport and Recreation gives further guidance on the provision of open spaces and playing fields.
The conditions for Suds use are slowly evolving and in addition to flood risk, consideration of a development’s impact on water quality and bio-diversity is now advocated by government agencies. In July, 2001, PPG25: Development and Flood Risk, actively encouraged the use of Suds within sustainable development.
DCLG carried out a consultation earlier this year on strengthening flood risk guidance with a new Planning Policy Statement (PPS) 25: Development and Flood Risk. The final document has not yet emerged but the intention is that PPS25 shall replace PPG25.
In its current draft form, PPS25 strengthens current guidance to include flood risk assessments at all levels of planning and stipulates the use of Suds wherever practicable. The paper encourages the development of joint strategies by planning authorities, sewerage undertakers and the EA to further advance Suds use and promote the early clarification of Suds ownership and maintenance responsibilities.
If implemented in its current draft form, PPS25 will require developers to undertake a Flood Risk Assessment (FRA) for all new developments and to provide clear evidence supporting drainage proposals if they are not using Suds. This is a particularly significant development because it will require extensive drainage investigations much earlier in the planning process. The presumption will change in favour of Suds, meaning they will have to be used unless developers can demonstrate them to be impractical. Proposals to make the EA a statutory consultee for development in flood risk areas should also ensure that the guidance is more effectively applied in vulnerable areas.
In addition to PPG25, the Water Framework Directive has raised our awareness of water quality issues. The directive embodies the concept of river basin management and by 2015 sets out to have:
- Prevented further deterioration, and protected and enhanced the status of rivers and wetlands
- Promoted sustainable water consumption
- Phased out discharges, emissions and losses of priority and hazardous substances
- Progressively reduced the pollution of groundwater
- Contributed to mitigating the effects of floods and droughts
The above government initiatives raise the priority of flood risk and drainage in the planning process and should lead to more considered flood risk management in future.
And, while the insurance industry has stated its intent to provide insurance cover to as many properties as possible, the appropriateness of the cover available to individuals and businesses will depend upon the approach to flood risk management in the catchment.
Economics will also be a significant driver for change, especially where water resources are scarce and the threat of flooding is highest. These problems will be exacerbated if current climate change predictions are proved correct and plans for nearly four million new UK homes by 2021 realised. A high proportion of these homes is to be built within existing flood plain areas and in the Southeast, which is also vulnerable to water supply shortage.
We must consider the potential effects of further urbanisation and climate change on the water environment if we are to protect property from flooding and enjoy a secure water supply in future.
While there are some local Suds successes, the most notable obstacle to Suds use is adoption. And, despite the introduction of the Interim Code of Practice for Suds by Ciria in July 2004, progress remains slow. The framework document provides a set of core standards and agreements from which responsibilities for future maintenance and ownership is determined. But, for water companies and local authorities, the recovery of future operation and maintenance costs remains a stumbling block.
However, while Suds adoption is a significant barrier to sustainable water management, experience at a local level suggests that poor understanding of techniques and improper regard to water quality and local biodiversity issues is the dominant obstacle to Suds use in the UK.
EIC’s Water Pollution Control Working Group will launch its Suds position paper shortly, identifying proposals that, if adopted, will overcome many of the legislative and regulatory barriers currently preventing the uptake of Suds.