Flood Risk and Sustainable Drainage

27 01 2016

Urgent information for Property Developers, Architects and Planning Consultants

Repeated flood events make headlines and maintain pressure on government for action.  Flood events can occur at any time of the year and do so with increasing frequency. The latest areas affected being the North West of England and parts of Scotland over Christmas 2015/16.

Surface water (or pluvial) flooding is the most common type of flooding, and is caused by periods of intensive rainfall or of extended duration.

Sustainable Drainage (techniques that retain surface water runoff on the land where the rain falls) are regarded as an essential part of any planned development.  These techniques reduce the risk of “flash-flooding” which occurs when rainwater rapidly flows into the public sewerage and drainage systems.

The UK government has committed that SuDS (Sustainable urban Drainage Systems) will be a part of all major planning applications from April 6th 2015.

“Defra quietly published Sustainable drainage systems: non-statutory technical standards on the Gov.uk website on 23 March 2015”: (LASOO: The Local Authority SuDS Officer Organisation).  The four page document addressed mainly technical issues relating to the design, maintenance and operation of SuDS.

Previously in December 2014, the Department for Communities and Local Government had announced the intention to publish changes to Planning Guidance that will help to increase the use of the sustainable drainage systems.

In the absence of any specific Planning Guidance appearing to date, LASOO has published their own version, in the form of Practice Guidance, a 32 page document which may be downloaded here

The LASOO document emphasises that flooding and drainage issues should be considered at the earliest opportunity, to a greater level of detail, and at every stage of the Planning process.  The guidance dramatically increases the analysis and design to be covered by the Drainage Strategy; a summary document which sets out how the Developer will address the drainage and flood risk of the site.

The following table summarises the flood risk and drainage information that should be available to the Local Planning Authority at the various stages of the Planning Application.
drainage table

By demanding extended drainage information at the Outline Planning Application Stage, the increasing uptake of the LASOO guidance potentially adds to Developer‘s speculative costs.

The Stilwell Partnership has had extensive experience in the assessment of Flood Risk and the design of SUDS.  From early Flood Risk Assessments for the new PPS25 in 2006, we have produced numerous drainage strategies and detailed SuDS schemes for individual bespoke building projects and major developments.

For local authorities and parish councils we continue to provide a wide range of services.  In 2008, we advised Local Authorities on the implications of the Pitt Report of the Flooding of 2007.  We continue to support Local Authority development control departments by validating design calculations for Planning Applications.  We undertake the engineering design of watercourse improvements and flood alleviation measures.

For Planning Applications, The Stilwell Partnership can offer advice for prospective developments.  This would identify, at the earliest stage, the risks and costs associated with meeting the Local Planning Authority’s requirements.  Contact our offices to discuss your project.

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