SUDS - where there's a will...
The use of sustainable urban drainage has been limited to flood risk management. However, the EIC's Water Pollution Control Working Group believes further benefits can be provided and is publishing a paper - the SUDS Position Paper - outlining what those are. Richard Whale explains.
This is especially true for catchments where the public sewer has insufficient capacity to receive an unrestricted surface water discharge from the proposed development.
The Environmental Industries Commission's (EIC) Water Pollution Control Working Group believes that this is a missed opportunity and are currently preparing a Position Paper identifying legislative and regulatory barriers to the take up of SUDS.
The 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 the Construction Industry Research and Information Association (CIRIA), which has published several best practice 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 development that uses land efficiently. We understand new housing development in England is currently built at an average of 25 dwellings per hectare; of which more than 50% is built at less than 20 dwellings per hectare.
This, according to the ODPM, represents a level of land take which is historically very high and which can no longer be sustained. Consequently, PPG3 directs planners to approve development that provides 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 frequently curtailed because of their influence on the width of the highway corridor.
An emphasis on flood risk management and maintaining high residential densities has steered drainage engineers towards solutions that have the smallest impact on the development footprint. Consequently, below ground attenuation techniques using oversized pipes or tanks are routinely used, with the natural hydrology of a site rarely considered in detail during the planning process.
These below ground attenuation systems provided are often submitted to the sewerage utility 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 and PPG3 as the latter 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.
Furthermore, local planning authorities should have clear policies for incorporating sufficient green open spaces in new housing developments if they are not already adequately provided within easy access. PPG17: Sport and Recreation gives further guidance on the provision of open space and playing fields.
The conditions for SUDS use are slowly evolving and in addition to flood risk, our consideration of a development's impact on water quality and bio-diversity is now advocated by Government and their agencies. For England, Planning Guidance 25: Development and Flood Risk, July 2001 (PPG25) sets out the precautionary principle for dealing with flood risk within a sustainable development.
The guidance note actively encourages the use of SUDS as part of its precautionary principle.
The Office of the Deputy Prime Minister now seeks to strengthen its flood risk guidance and has recently published its consultation paper - Planning Policy Statement (PPS) 25: Development and Flood Risk - for our consideration. 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 joint strategies of planning authorities, sewerage undertakers and the Environment Agency (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 development and provide clear evidence supporting drainage proposals if not using SUDS.
This is a particularly significant development as it will require extensive drainage investigations for a site earlier in the planning process.
The presumption will be in favour of SUDS unless it can be shown 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 the further deterioration, 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.
Economics will also be a significant driver for change, especially where water resources are scarce and the threat of flooding is at its 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 proposed to be built within existing floodplain areas and in the South-east, which is also vulnerable to water supply shortage.
There can be no doubt that 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 the future.
Whilst there are some local sustainable urban drainage system successes, the most notable obstacle to SUDS use is adoption and despite the introduction of the Interim Code of Practice for SUDS, CIRIA 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.
However, for water companies and local authorities, the recovery of future operation and maintenance costs remains a stumbling block.
However, whilst SUDS adoption is a significant barrier to sustainable water management, experience at a local level suggests that poor understanding of SUDS techniques and improper regard to water quality and local biodiversity issues presents the dominant obstacle to SUDS use in the UK.
EIC's Water Pollution Control Working Group will launch the SUDS Position Paper shortly. The paper will identify a number of different proposals that, if adopted, will overcome many of the legislative and regulatory barriers currently preventing the take up of SUDS.
Richard Whale works for Atkins Water & Environment, and is also with the EIC Water Pollution Control Working Group.
T: 01925 238302.