Sustainable Urban Drainage Systems (SuDS) manage surface water run-off as close to its source as possible. This reduces the potential impacts and risks of surface water flooding, fluvial and tidal flooding- by reducing the peak flows entering the rivers, the sea and the sewers.

Whether you are a property developer, architect, land owner or planning consultant this complete guide to SuDS and SuDS design and reports sets out to teach you all you need-to-know about how they work and how they can affect your proposed development.

In certain situations, a Sustainable Urban Drainage System (SuDS) assessment is a compulsory requirement at planning application stage. In England, from April 2015, it became compulsory for SuDS to be considered in planning applications for major developments, and Lead Local Flood Authorities quite often request SuDS at planning application stage for minor developments also.

Unfortunately, a lot of the information in this area can be full of jargon or disconnected. Let’s address that, by taking a look at the key information regarding SuDS in a simple and clearly approached way.

In this guide, we will cover:

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How do sustainable drainage systems (SuDS) work?

Surface water arising from a developed site should, as far as practicable, be managed in a sustainable manner to mimic the surface water flows arising from the site prior to the proposed development, while reducing the flood risk to the site itself and elsewhere, taking climate change into account. Reducing the rate of surface water discharge from Urban Sites is one of the most effective ways of reducing and managing flood risk.

Traditional piped surface water systems work by removing the surface water from our developments as quickly as possible, however this can cause various adverse impacts:

  • Increased downstream flooding, and sudden rises in flow rates and water levels in local water courses.
  • Reduction in groundwater levels dry weather flows in watercourses.
  • Reduce amenity and adversely affect biodiversity due to the surface water run-off containing contaminants such as oil, organic matter and toxic materials.

So how exactly does the process work?

SuDS are defined as a sequence of management principles and control structures designed to drain surface water in a more sustainable fashion than conventional piped drainage techniques. SuDS should utilise the environmental, ecological and social benefits of a site.

These include:

  • Protection and enhancement of water quality – As well as providing on-site attenuation, SUDS treat the water, resulting in an improved quality of water leaving the site. This is achieved when the water passes through the fine soils and the roots of specially selected plants, pollutants washed of the hard landscaping by rainfall will be safely removed before the water reaches the natural water course.
  • A sympathetic approach to the environmental setting by providing the opportunities to create habitats for flora and fauna in urban watercourses and open spaces.
  • Meeting the amenity and social needs of the local community and residents in the creation of attractive green spaces.

The various types of SUDS include: 

  • Permeable paving
  • Soakaways and other infiltration devices, meaning that no surface water run off leaves the site
  • Swales and basins
  • Bioretention/rain gardens;
  • Green or sedum roofs
  • Living/Green Walls
  • Rainwater re-use
  • Infiltration trenches and filter drains
  • Ponds and wetlands
  • Attenuation Tanks


Benefits of SuDS

Sustainable drainage systems shouldn’t be viewed as a ‘mandatory system’ or a means to an end. There are a huge array of benefits to implementing SuDS in your project(s).

The benefits of sustainable drainage systems include:

Planning consent: SuDS implementation at this stage can drastically increase your chances of achieving planning consent the first time round, as well as investigating whether or not SuDS are achievable at your site, rather than to be dealt with a planning condition post planning, and then to find out that there is no point of discharge and the development is not feasible due to the SuDS and Surface water condition not being discharged.

Reduce risk: They can reduce the risk of flooding to your development and surrounding areas.

Cost reduction: Well considered and sited SuDS at planning stage can reduce the cost of any attenuation required, as well as utilising the landscaping areas to provide above ground SuDS, that will not only treat the surface water from the site, but also reduces the peak flow rate of this.

Biodiversity: Due to increased urbanisation over the years, not only has the risk of flooding increased, there has also been a vast reduction in wildlife and biodiversity due to this. Sustainable Urban Drainage Systems biodiversity at the site, which in turn attracts wildlife as well as creating amenity value at your site, by making the site more attractive to those living and working in the area.


What is the purpose of a SuDS report/assessment?

A SuDS assessment or SuDS report is carried out as part of a planning application, to ensure that developers have considered the surface water run off from their proposed development, and followed the SuDS hierarchy to ensure that this is dealt with via the use of Sustainable Urban Drainage and aims to manage surface water as close to its source as possible, and thereby prevent flooding in new developments, and elsewhere, within the vicinity of the site.

SuDS reports are a crucial component in supporting planning applications, from concept to post-approval planning conditional discharge. Involving a SuDS report specialist from the outset will ensure a smooth planning process, avoidance of delays and fewer costs further into the development.

When would a SuDS report be required?

  • To validate planning applications during pre-planning stage/planning application stage
  • To discharge planning conditions relating to SuDS and Surface Water Run off
  • To ensure the Surface Water run off arising as a result of their development proposals is managed through the use of SuDS, in order to reduce the flood risk at the site and elsewhere
  • To gain BREEAM Surface Water Run off credits


What are planning conditions?

In the event of a planning application being granted, the governing local authority will insist that a number of conditions are met. These can include anything from building materials, estimation of time, ecology, mitigation matters, Sustainable Urban Drainage Systems drainage, and foul and surface water drainage, to name a few. Once these conditions have been met, the developer will be allowed to commence the construction of their development. Until these conditions have been met and released, you will not be allowed to commence construction at their site.

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Are SuDS and SuDS reports compulsory?

In many situations, a Sustainable Drainage Systems (SuDS) assessment is a compulsory requirement. It became compulsory, in April 2015, for SuDS to be considered in planning applications for any major developments.

Are SuDS Reports in Wales Compulsory?

For Wales, however, these laws differ slightly – there it is now a mandatory requirement for any construction work to not begin until a SuDS system has been approved by a SuDS Approval Body (SAB). This relates to all new developments of more than one property or where the construction area is greater than 1000m2.

SuDS can generally be included within most developments, as long as they are taken into consideration early in the planning and development processes.

If a sustainable drainage system cannot be implemented on a site, the development proposals may not be viable until SuDS can be accommodated.


What is included in a SuDS report/assessment?

At Nimbus, we use a holistic approach to SuDS reports, wherein the aim is to carry out all the necessary work from beginning to end, to make things as painless as possible for the developers(s).

Nimbus Engineering’s SuDS reports include the following, as per the relevant local authorities’ requirements and is bespoke to the unique nature of your development:

  • Flood Risk Assessment: assessing the flood risk from all sources, and providing mitigation measures where necessary (a requirement for planning applications for all major developments within Flood Zone 1, or any developments within a Flood zone 2 and 3)
  • Pre- and post-development surface water run off calculations and hydraulic modelling using industry standard software
  • Pre-development contributing area and exceedance route plans
  • Post-development contributing area and exceedance route plans
  • Percolation/Infiltration tests to BRE365 standards
  • BRE365 Soakaway Sizing calculations and hydraulic modelling
  • Surface water attenuation calculations and hydraulic modelling
  • Assessment of SuDS hierarchy in line with the local and national policies
  • Proposed SuDS strategy in line with local and national policies
  • Outline SuDS Design layout plans for your development
  • Detailed SuDS Design plans, to show feasibility to the LLFA, Building Regulations and for Construction
  • Management, and maintenance plan reports for the SuDS for the lifetime of the development
  • Describe the existing and proposed drainage arrangements for the site.
  • Calculate the existing and proposed surface water runoff for the site using industry standard software.
  • Assess the suitability of the varying SuDS options, by going through the SuDS hierarchy and to propose appropriate elements (e.g. green roofs, raingarden planters, raingardens, rainwater harvesting, soakaways, ponds, attenuation tanks) to meet the runoff rate requirements for the site based on national and local planning policy.
  • Provide an indicative drainage layout for the site, showing the layout and location of the proposed drainage measures.
  • Detailed design of the surface water network and SuDS systems, provided via layout plans and detailed drawings
  • Complete the SuDS report as a standalone document, or incorporated within a Flood Risk Assessment report for the site.

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Will I need to carry out any other drainage reports?

Depending on the size, location and type of your project(s), it is possible that you may need a second-stage report. These are sometimes requested once the SuDS strategy has been accepted in principle or conditioned.

These further reports are known as ‘Detailed SuDS and Surface Water Network Design’, and they provide comprehensive layouts, long-sections and construction details.


Which properties require a SuDS report?

All new developments, regardless of size require SuDS to be incorporated in their design.

Whether a minor development requires a SuDS report for validation at the planning application stage, depends on the requirements of each Lead Local Flood Authority (LLFA).

However, as the risk of flooding is increasing year-on-year - these are being requested by most LLFA’s now, even for minor extensions.

As of 2015, national policy mandates that developments of more than 10 units, or commercial or industrial developments (classified as major), do require a Flood Risk Assessment and SuDS Strategy report to validate and support the planning application. The level of detail required in these reports can vary depending on the application type.


Nimbus’ approach to sustainable drainage system reports

Any professional involved in the development of a construction project needs a solution that ensures compliance, is cost effective, sticks to timescales and is tailored to the individual requirements of your site.

Through a holistic approach, Nimbus Engineering ensures that your SuDS report is carried out from beginning to end, so the customer doesn’t have to worry.

As experts in this area, the assessments are guaranteed to take into consideration critical elements of your site development, such as whether it is in an at-risk or critical drainage area, in order to provide you with guidance and compliance with the relevant authorities and bodies.

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As you can see, there is a lot of information to digest regarding SuDS and SuDS Reports. We hope that this post has answered your pressing questions, so you can be more confident during your next development project.

Whilst there are an array of regulations regarding SuDS reports and surface water management, the best advice is to be prepared and think about these systems early in your development process. Very often, the client’s leave little space on their site for Sustainable Urban Drainage Systems.

Through preparation and knowledge, you can avoid complications down the line and even prevent extra costs from being added unexpectedly.

If you still have any unanswered queries regarding SuDS and SuDS assessments, please do not hesitate to get in touch with a Nimbus expert today. We are always happy to help.

Sadia Luckett

Written by Sadia Luckett

Sadia Luckett is the Director at Nimbus Engineering, specialising in foul and surface water drainage & SuDS.