Sustainable urban drainage systems SUDS

[edit] What are SUDS?

Sustainable urban drainage systems (SUDS) are systems designed to efficiently manage the drainage of surface water in the urban environment. Sustainable urban drainage systems can provide an alternative to, or addition to, traditional drainage systems where surface water is drained directly and quickly into underground, piped drainage.

[edit] Why are SUDS necessary?

As population has increased, particularly in urban areas, and ‘soft’, permeable landscape has been replaced with hard surfaces, surface water runoff has reached traditional piped drainage faster and in larger quantities. This has been exacerbated by the loss of rural features that might once have slowed the passage of surface water, being replaced with large, intensively farmed fields that rapidly discharge surface water into piped drainage or waterways that make their way into urban areas. The result has been higher peak flows and serious flooding of urban areas, pollution, damage to habitat and contamination of groundwater sources.

Sustainable urban drainage systems are likely to become even more important as population increases, water resources are put under increasing pressure, and the impact of climate change is felt.

In February 2019, The Association of SuDS Authorities (ASA) was launched to promote the use of SuDS in property developments.

[edit] How do SUDS work?

Sustainable urban drainage systems aim to mimic 'natural' drainage by adopting techniques to deal with surface water runoff locally, through collection, storage, and cleaning before allowing it to be released slowly back into the environment.

According to CIRIA, ‘SUDS techniques seek to capture, use, delay or absorb rainwater, rather than reject it as a nuisance or problem. Sustainable drainage delivers multiple benefits. As well as delivering high quality drainage whilst supporting areas to cope better with severe rainfall, SuDS can also improve the quality of life in developments and urban spaces by making them more vibrant, visually attractive, sustainable and resilient to change by improving urban air quality, regulating building temperatures, reducing noise and delivering recreation and education opportunities.’

[edit] What strategies can be adopted for SUDS?

Sustainable urban drainage systems might adopt strategies to:

• Reduce the likelihood of pollutants reaching watercources.
• Reduce runoff by reducing impermeable areas.
• Store runoff through attenuation.
• Allow water to infiltrate into the ground.
• Convey water slowly on the surface (where it is easy to inspect and can provide local amenity and habitat for wildlife).
• Allow sediments to settle out.
• Only then, and only if it cannot be dealt with on site, conveying runoff off site, but even then doing so slowly.

SUDS techniques might include

• Filter strips and drains.
• Swales.
• Permeable surfaces.
• Basins and ponds.
• Underground storage.
• Wetlands.
• Green roofs.
• Rainwater harvesting.

Sustainable urban drainage systems should be considered during the site selection process. Different management strategies may be required for different parts of a site, and flows from roofs should also be considered.

[edit] What are the benefits of SUDS?

The benefits of sustainable urban drainage systems can include:

• Reducing flooding.
• Reducing the demand on existing drainage systems (potentially making a development viable in an area where it might otherwise not be viable).
• Enhancing water quality.
• Reducing pollution.
• Providing habitats for wildlife.
• Providing local amenity.
• Recharging groundwater and watercourses resulting in a reduced risk of drought.

[edit] Legislation

In October 2012, Schedule 3 of the Flood and Water Management Act 2010 came into force. This created the power to require the inclusion of sustainable drainage of surface water in developments that need planning approval or have drainage implications. It removed the automatic right, established by the Water Industry Act, to connect to public sewers and instead gave powers to local authorities as SUDS Approving Bodies (SABs) to approve new drainage systems and their connection to public sewers.

It was intended that sustainable drainage systems would be assessed relative to a new national standard that would address the way drainage systems are designed, constructed, maintained and operated, considering run-off destination, peak flow rates, volume and water quality. The requirements of Schedule 3 were intended to be phased in over 3 years. Initially only major developments would have to submit sustainable drainage proposals for approval, but from October 2015 all developments of more than one house would need to seek approval.

However, in December 2014, the government announced that from April 6 2014, planning authorities would be given authority for approving SuDS on developments, not SuDS Approving Bodies. In addition it was announced that a threshold of 10 dwellings or more, or equivalent non-residential or mixed development will apply. See SuDS consultation for more information.

On November 13 2015, CIRIA published The SuDS Manual (C753) which it described as the most comprehensive industry SuDS guidance available in the UK Intended to support uptake, manage floods and create better places and spaces. It deals with the planning, design, construction, operation and maintenance of SuDS. Its publication followed a ministerial statement made by the Secretary of State for Communities and Local Government earlier in 2015 which made it clear that SuDS must play a greater role in the planning system, and that it is a requirement in new major developments wherever appropriate.

On January 11 2022, the Flood and Coastal Erosion Risk Management Research and Development Programme published its Assessment of How Strategic Surface Water Management Informs Sustainable Drainage Systems (Suds) Delivery in Developed Areas Through Spatial Planning and Development Management - WT15125. This research identified a number of areas of improvement and presented 30 conclusions for the Government to consider.

On January 10 2023, DEFRA published "The review for implementation of Schedule 3 to The Flood and Water Management Act 2010". This report sets out the findings of a review which recommends implementation subject to final decisions on scope, threshold and process once a full regulatory impact assessment has been completed. The assessment will look at different options and the expected costs and benefits. The government has accepted this recommendation. Defra will carry out a consultation in order to collect views on the impact assessment, national standards and statutory instruments in 2023.

The National Planning Policy Framework (NPPF), published by the Ministry of Housing, Communities and Local Government in December 2024, states: ‘A sustainable drainage system controls surface water run off close to where it falls, combining a mixture of built and nature-based techniques to mimic natural drainage as closely as possible, and accounting for the predicted impacts of climate change. The type of system that would be appropriate will vary from small scale interventions such as permeable paving and soakaways that can be used in very small developments to larger integrated schemes in major developments.’

[edit] Related articles on Designing Buildings

• Achieving sustainable clean water infrastructure for all.
• Blackwater.
• Blue roof.
• BREEAM Surface water run-off.
• Catchment flood management plans.
• Dewatering.
• Drainage.
• Eutrophication.
• Flood.
• Flood and Water Management Act.
• Flood insurance.
• Flood risk.
• Flood risk management plan.
• Floodscape.
• Future flood prevention.
• Future Water, The Government’s water strategy for England.
• Greywater.
• Groundwater control in urban areas.
• Highway drainage.
• Pitt Review.
• Planning for floods.
• Pumps and dewatering equipment.
• Rainwater harvesting.
• River engineering.
• Sewer construction.
• Sewerage.
• Soakaway.
• SuDS infographic.
• Surface water
• Sustainable urban drainage systems - latest guidance.
• Sustainable water.
• Swales definition.
• The SuDS Manual.
• Water Act 2014.
• Water consumption.
• Water engineering.
• Water transfers and interconnections.
• Why creating new ponds helps to protect the ecosystem.

[edit] External references

• Construction Industry Research and Information Association.
• CIRIA BeST (Benefits of SuDS Tool, W045), a new, free Excel tool for use on PC.
• Sudsnet.
• SUDS Wales.
• British Geological Society: SUDS.

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