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Sustainable drainage requirements for planning applications

Drainage is now a material planning consideration for the Local Planning Authority. Any new developments or redevelopment should ensure their drainage system utilises sustainable drainage.

What are Sustainable Drainage systems?

Approaches to manage surface water that take account of water quantity (flooding), water quality (pollution) and amenity issues are collectively referred to as Sustainable Drainage Systems (SuDS). SuDS mimic nature and typically manage rainfall close to where it falls. SuDS can be designed to slow water down (attenuate) before it enters streams, rivers and other watercourses.

CIRIA's susdrain project has launched a new animation shown below, on Sustainable Drainage Systems (SuDS) that provides an engaging and digestible overview of SuDS.

There are a large variety of drainage options available including green roofs, permeable paving, swales and ponds.  

SuDs information required for major applications

Sustainable drainage systems (SuD's) are now a material planning consideration for major developments (ie developments of 10 dwellings or more and equivalent non-residential schemes), and decisions on planning applications from this date will be expected to make sure that SuD's are in place to ensure surface water is controlled on site. 

All major applications should adopt the approaches, provide the information and meet the standards explained within the Hillingdon SuDs Design and Evaluation Guide. An application should as a minimum contain and demonstrate the following: 

  1. To speed up the review of proposals by the Lead Local Flood Authority, please provide summary information in the form of the following  Volumes and Flows Proforma [41kb].
  2. Detailed site layout at an identified scale.
  3. Topographical survey of the site.
  4. Inclusion of maps showing the current risks to and from the site, from topography, such as overland flow routes.
  5. Plans, drawings and specification of SuD's proposed. This should include detail of hard construction, soft landscaping and planting, as well as routes flow will take should the drainage system be exceeded.
  6. Demonstration of the consideration of the spectrum of SuD's in accordance with the SuD's hierarchy, and clear justification provided where a traditional piped drainage system is provided.
  7. Calculations must adhere to the revised Environment Agency guidance on Climate Change produced in Jan 2016. This requires attenuation to be provided for Commercial 1 in 100year plus 20% and residential 1 in 100 year plus 40%.
  8. Calculations should be provided to demonstrate water is controlled to green field run off rates, at a variety of return periods- off site works.
  9. A 5l/s rate should not be used as a minimum, as flow control devices have evolved to allow smaller discharge rates.
  10. S106 may be considered for off site works where space is limited.
  11. Information on the receptors of the drainage system. Where infiltration is proposed a suitable site investigation must be provided including information on groundwater levels, or sizing for a tanked or no infiltration must be assumed, together with necessary consents ie statement from any water utilities that there is suitable capacity in the foul and surfaces water networks or if not that suitable upgrades have been agreed. Methods of appropriate water quality control to be provided.
  12. Management and maintenance plan for all SuD's to be provided. To ensure there is ongoing maintenance over the lifetime of the development, a management and maintenance plan will be expected to be provided along with the details of the body legally expected to maintain the system where it is anyone other than a single private land owner. Conditions will be added to planning decisions, or developers will be expected to enter into a legal agreement under S106 of the Town and Country Planning Act 1990 (as amended). An example of an appropriate management plan can be found on Susdrain - Useful frameworks and checklists.

Water sensitive design Water Pipe Art

As the London Borough of Hillingdon is in an area where water resources are provided generally from groundwater supplies and these are heavily abstracted.

It is expected that drainage proposals should include some at source water collection and water reuse, through the provision of rainwater harvesting tanks or even water butts, or grey water recycling. This is to minimise water use proportionate with the scale of the proposed development.

Minor applications and householder development Green Roof Lake Farm School

Minor development where it lies within a critical drainage area and or is identified to lie in an area likely to be at risk from surface water flooding from the Environment Agency Flood Map, are also required to provide information on the sustainable drainage provided on site.

Permeable front gardens

The General Permitted Development Order 2008 requires any work done to front gardens under permitted development to be subject to the following condition:

  • where the area of ground covered by the hard surface, or the area of hard surface replaced, would exceed five square metres:
    • either the hard surface shall be made of porous materials
    • or provision shall be made to direct run-off water from the hard surface to a permeable or porous area or surface within the curtilage of the dwelling house
  • or the work would require a planning application

This is to ensure front gardens remain permeable where people wish to use them as driveways so they don't contribute to flooding. There is increasing demand on the capacity of surface water sewers and often a situation where the water company will not increase the capacity of the sewer. For guidance on how to comply with requirements for front gardens the Royal Horticultural Socity has produced a useful booklet 'Gardening Matters - Front gardens' or Hillingdon Council has produced a leaflet on  paving front gardens [206kb].

Report non compliance to our planning enforcement team

Please call the Customer Contact Centre on 01895 2506000 or contact@hillingdon.gov.uk

If have any other queries regarding the information on this page, please call the Customer Contact Centre and ask to speak to the Flood and Water Management Officer or email flooding@hillingdon.gov.uk.

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Article utilities:  Bookmark and Share Print Print this page Last updated: 08 Mar 2018 at 14:44