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Herrington Consulting has significant experience in developing and appraising surface water management strategies. The latest version of the NPPF (2019) requires all new development to consider Sustainable Drainage Systems (SuDS), with a view to reducing flood risk. Alonside this, the Non-Statuatory Technical SuDS Standards (NTSS) apply for all major devleopment and as such, it must be demonstrated that the development does not exacerbate the risk of flooding elsewhere. A Surface Water Management Strategy (SWMS) is therefore required to be included as part of the planning submission and in some cases can be included within the FRA.

The overartching aim of a drainage stratgey is to ensure that the design of the surface water drainage for housing developments avoids, reduces and delays the discharge of rainfall run-off to watercourses and public sewers using SuDS. The objective is to protect receiving waters from pollution and minimise the risk of flooding and other environmental damage.

Surface Water Management Strategy

Whilst a site may be shown by the Environment Agency's/SEPA's flood zone maps to be within a low risk zone (Zone 1); an area defined by the flood maps as having a low annual probability of flooding from the sea or a main river - the risk of flooding from other sources such as groundwater, overland flow, sewers etc, may still be present.

For sites that exceed 1 ha in area or, are identified by the planning authority as being a site with problematic drainage or localised flooding issues, Planning Policy requires that a Flood Risk Assessment (FRA) is undertaken so that such risks can be identified and mitigated. Of equal importance is the requirement to ensure that the proposed development does not exacerbate the risk of flooding elsewhere.

In order to appraise the impact of a new scheme, a Surface Water Management Strategy (SWMS) can be developed as either a stand-alone study, or be included as part of a Flood Risk Assessment. In most cases the SWMS is based on a desk-top study that tests the application of the preferred hierarchical approach to surface water discharge, i.e. via infiltration, connection to a watercourse or to a public sewer. Planning Policy also promotes the use of Sustainable Drainage Systems (SuDS) and therefore the SWMS will investigate the appropriateness of incorporating a range of SuDS elements within the surface water drainage system.

Herrington Consulting has range of numerical models that assist in the development of SWMS, including FEH, ReFEH and Micro Drainage Source Control. For complex sites direct rainfall 2D overland flow path and flood route modelling can also be undertaken using Surface-water Modelling System & TuFLOW.

If the preferred method of surface water discharge is via infiltration then it is likely that the SWMS will need to be supported by site-specific soakage tests. We would not normally undertake these ourselves, however, we can advise on appropriate methodologies if required.

To prepare the surface water management strategy we will often require topographic information of the site. Once again we would not normally undertake a topographic survey ourselves, however, we can provide you with a quotation for a surveyor to undertake a survey with the appropriate level of detail.


Urban drainage is moving away from the conventional thinking of designing for flooding, to balancing the impact of urban drainage on flood control, quality management and amenity. Surface water drainage methods that take account of quantity, quality and amenity issues are collectively referred to as Sustainable Drainage Systems (SuDS). These systems are more sustainable than conventional drainage methods because they:

  • Manage runoff flowrates, reducing the impact of urbanisation on flooding
  • Protect or enhance water quality
  • Are sympathetic to the environmental setting and the needs of the local community
  • Provide a habitat for wildlife in urban watercourses
  • Encourage natural groundwater recharge (where appropriate).

These systems do this by dealing with runoff close to where the rain falls, managing potential pollution at its source and protecting water resources from point pollution. The underlying philosophy of SuDS is to replicate as closely as possible the natural drainage from a site before development and to treat runoff to remove pollutants, thereby reducing the impact on receiving watercourses.

Until now, the use of SuDS has been fairly limited and usually only considered by developers when conventional drainage options are not suitable or if trying to create a 'green' development. However, this is changing as SuDS and surface water management forms a key component of the Flood and Water Management Act 2010. The Act implements many of the recommendations identified through the Pitt Review of 2008, following the devastating floods during the summer of 2007. In March 2015, the Non-statutory Technical Standards for Sustainable Drainage Systems (NTSS) was released and in 2019 the NPPF was updated to ensure all development considers the use of SuDS.

The NTSS are designed to provide a structure for the Lead Local Flood Authorities (LLFAs) to make judgment on the acceptability of drainage schemes for developments and redevelopments. They are an essential part of the Government's proposals to encourage widespread SuDS adoption in England and Wales and prevent the automatic connection of surface water drains to the public sewer network.

By talking to us you can ensure that solutions to overcome difficult drainage problems are not overlooked and opportunities to make economic savings and social and environmental enhancements are not missed.

Herrington Consulting is a specialist consulting practice providing bespoke solutions that help our clients to reduce the risk of flooding, from both urban and natural sources. The services we offer range from providing advice on the suitability of particular systems to detailed design. Regardless of the size of development, we can add value, so why not contact us today for a free of charge, no obligation quotation.

SuDS Planning Condiitons / SuDS Design / BREEAM

Following award of planning, it is standard practice for the Local Planning Authority (LPA) to request more detailed information in relation to how a development will be drained. This is often enforced through a Planning Condition relating to SuDS.

As a consultant that specialises in flood risk management and hydraulic modelling we are ideally placed to provide the reports required to demonstrate compliance with the LPA's (and Lead Local Flood Authority's) requirments.

Drainage Conditions - The aim of a planning discharge report is to ensure that the design of the surface water drainage for developments avoids, reduces and delays the discharge of rainfall run-off to watercourses and public sewers using Sustainable Drainage Systems (SuDS). The objective being to protect receiving waters from pollution and to minimise the risk of flooding and other environmental damage.

The assessments that we undertake include the following:

  • Calculation of pre and post development impermeable areas
  • Calculation of peak rates of runoff in accordance with the requirements of the CfSH
  • Calculation of pre and post development volume of runoff
  • If the proposed development results in additional runoff, then infiltration techniques are examined to prevent this leaving the site.
  • If infiltration is not appropriate due to soil types, contamination, space restrictions etc, then methods for limiting the post development peak discharge to the 'limiting discharge' will be examined.
  • Examination of the impacts of local drainage system failure
  • Advice on the appropriate use of SuDS
  • BRE Environmental Assessment Method BREEAM

    BREEAM sets the standard for best practice in sustainable building design, construction and operation and has become one of the most comprehensive and widely recognised measures of a building's environmental performance.

    Herrington Consulting can provide detailed reports that fulfil the Flood Risk and Surface Water Runoff Criteria required for a BREEAM Assessment, enabling BREEAM assessors to gain additional credits for these elements.

    We work closely with both developers and Code Assessors to ensure that the maximum number of credits can be achieved. For a free, no obligation quotation please use the Contacts page to supply us with the information for your specific project.

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