Planning advice, fees and application forms

Sustainable drainage requirements and SuDS

Sustainable drainage is now a material planning consideration for the local planning authority.

Other advice and guidance on managing flooding, including flood risk assessments, can be found on our Flooding page.

Any new developments or redevelopment should undertake suitable development planning to ensure a water sensitive urban design. This design should incorporate sustainable drainage to help create beautiful, successful and resilient places.

What are sustainable drainage systems?

Sustainable Drainage Systems (SuDS) are ways of managing surface water that account for water quantity (flooding), water quality (pollution) and amenity issues. SuDS mimic nature and usually manage rainfall close to where it falls. They can slow down water before it enters streams, rivers and other watercourses.

There are many drainage options available, including green roofs, permeable paving, swales and ponds. For a visual overview of SuDS, watch CIRIA's animation created for its susdrain project.

Minor applications and householder development

SUDS drainage example
Minor development can also cumulatively affect flood risk. 

This is because it increases demand on the capacity of surface water sewers but often the water company will not increase the sewer's capacity. Small scale development can and should contribute to reducing flood risk by ensuring all hard surfacing is made permeable.

All minor development should include plans showing down pipes are connected to soakaways or other methods of control and not the sewer.

Requirements for front gardens

If it's completely hard surfaced, paving your front garden is not permitted development. For more guidance on how to comply with requirements:

Report non-compliance to our planning enforcement team

To report non-compliance, visit our planning enforcement page.

SuDS information for major applications

Sustainable drainage systems are a material planning consideration for major developments (that is, developments of 10 dwellings or more and equivalent non-residential schemes).   

Drainage is critical to be integrated within a scheme at an early stage. All major applications should adopt the approaches, provide the information and meet the standards explained within the Hillingdon SuDS Design and Evaluation Guide. Case studies can be found at Susdrain – the community for sustainable drainageThe SuDS manual, published by CIRIA, also provides clear, practical advice, diagrams, case studies and checklists.

To speed up the review of proposals, please ensure all consultants design to the appropriate standard of detail. This will also help you reduce the need for precommencement conditions.

An application should as a minimum contain and demonstrate the following points:

1. Summarise the proposals within the Hillingdon Suds Proforma (PDF) [396KB] or SuDS Proforma Excel Spreadsheet (Excel doc) [114KB] developed by LoDrainage Engineers Group and the GLA. Further guidance is contained within the notes.

  • Calculations must adhere to the revised Environment Agency guidance on climate change produced in Jan 2016. This requires storage to control surface water on site to be provided for up to the 1 in 100 year event plus 20 percent for commercial premises and storage for the 1 in 100 year plus 40 percent for residential development.
  • Calculations should be provided to demonstrate water is controlled to greenfield runoff rates, at a variety of return periods.
  • We expect a likely discharge rate of 1-2 l/s/ha. A 5 l/s rate should not be used as a minimum, as flow control devices have evolved to allow smaller discharge rates.
  • You can find useful tools on the HR Wallingford SuDS tool website.

2. Plans, drawings and specifications of proposed SuDS, integrated with landscaping and materials requirements. Design, drainage and landscaping consultants should coordinate and integrate plans.

  • Detailed site layout showing SuDS integrated with landscaping proposals. SuDS should contribute to green links and chains, as well as accessibility to the Blue Ribbon Network across Hillingdon.
  • Topographical survey of the current site showing aboveground ponding and overland flow routes, and proposed levels showing the changes to manage these risks as well as providing exceedance routes.

3. Consideration of the range of SuDS in accordance with the SuDS hierarchy, ideally using a variety of options. Where the most sustainable solution cannot be provided, you must justify why.

  • Hillingdon's water supply is generally provided from groundwater supplies. The level of water taken out affects the health of our local rivers. Therefore drainage proposals should include some at-source water collection and reuse through the provision of rainwater harvesting tanks or water butts, or grey water recycling. This is to proportionally minimise water use with the scale of the proposed development. If this cannot be achieved on site, more efficient sanitaryware will need to be retrofitted.
  • Even if infiltration is not possible, this does not mean water cannot be held above ground or conveyed above ground in the form of rain gardens and swales to provide green links across a site. These also provide wider environmental and amenity benefits, and the space could help you contribute to Biodiversity Net Gain requirements.
  • We expect to see a variety of drainage components within the scheme to ensure resilience of the system.

4. Information on the drainage system:

  • In order to inform the right choice of sustainable drainage system, a suitable on-site investigation must be provided including information on groundwater levels, not just a desktop study using nearby Borehole information.
  • Provide evidence the proposals connect into a wider functioning Thames Water or private network, for example that the point a proposal connects into is part of a wider network, with the appropriate agreements in place.
  • Discuss proposals with Thames Water's free pre-planning application service. This identifies any potential water and wastewater network reinforcement requirements. Developments which result in the need for off-site upgrades will be subject to conditions to ensure the occupation of the building does not outpace the delivery of necessary infrastructure upgrades. New connection charging information can also be found on the Thames Water website.

5. Methods of appropriate water-quality control:

  • Hillingdon has separate systems of drainage, so all surface water ends up in the local rivers. Appropriate controls should be included to capture and manage pollution.

6. Management and maintenance plan:

  • Provide a management and maintenance plan for all SuDS to ensure there's ongoing maintenance over the lifetime of the development. 
  • Individual land owners should not be responsible for a system which also serves other landowners. This should be made the responsibility of a Private Management Company or offered for adoption to the Water Utility.
  • This should also contain details of the standard of operation.
  • An example of an appropriate management plan can be found on Susdrain, under useful frameworks and checklists.

A legal agreement under S106 of the Town and Country Planning Act 1990 (as amended) may be considered for off-site works where these standards cannot be met. 

If you have any other queries regarding the information on this page, please email

Page last updated: 04 Aug 2023