SuDS (Sustainable Drainage Systems) have become more and more popular in recent years, and for good reason. Pretty much every development needs drainage systems in place to function effectively into the future, but how can you take that development from functional to environmentally beneficial?

Under the 2019 version of the National Planning Policy Framework, SuDS form one of five key considerations to the provision of development, when considering how to manage flood risk.  This puts SuDS at the centre of good development. This protects and enhances development for both people and the environment.

The use of SuDS as a central tool to reduce flooding was outlined in the Pitt Review, lessons learned from the 2007 floods. You can read this on the National Archives website here: Pitt Review PDF.

That’s where SuDS come in.

In this article, I’m going to go over the pros and cons of SuDs, a few different types of sustainable drainage options available, how it can affect your BREEAM certification, and the cost impact that they could have on your development project.

When rainfall lands on roads, buildings, car parks, and other impermeable areas, the amount of surface water run-off that drains off these surfaces is much greater than the equivalent greenfield area.

Traditionally, the run-off from hard landscaped areas would be collected by roof gutters, downpipes, and road gullies, and directed into a piped sewer network. Oftentimes, especially within older towns and cities, this collected water would be directed into the combined sewer network. This then mixes the relatively clean surface water with the dirty foul water.

When flash flooding happens, this would often lead to both the foul and surface water spilling out of the drainage network, causing flooding to people and property. However, it’s more common these days to provide separate foul and surface water drainage networks.

Either way, piped drainage systems have a limited capacity to accept extreme rainfalls. When this capacity is exceeded, flooding occurs.

With more homes and business being built, permeable surfaces that allowed the water to flow freely are being swapped for impermeable ones. This exacerbates the risk of surface water flooding and reducing groundwater supplies. This has the added issue of removing what was a natural filter for metal, pesticides, and animal waste that enters the water, which is happening much more frequently with urbanisation.

With climate change creating wetter winters and increased storm events, the level of surface water available will only increase, making the traditional drainage methods less and less effective.

These are the issues that Sustainable Drainage Systems are trying, and succeeding, to mitigate.

It’s also important to note that as of April 2015, if your new development is 10 or more homes, a major commercial build, or mixed use development you must include SuDS as part of your Planning Proposal. If your development falls into any of these, you have to use SuDS.

SuDs drainage systems reduce the impact of new and existing developments with respect to water in both rural and urban areas by replicated natural systems. In theory, they’re more cost effective (x, x, x, x, x) and have a very low environmental impact to collect, store, and/or clean water before it’s released back into the environment at a more controlled flow rate. This mimics the flow profile that occurred prior to development.

This is important because sustainable drainage is more about long-term effects of development. It takes into account social factors around drainage. It doesn’t just look at the quantity of water that needs to be removed from an area, but also the quality and how it may then be used to enhance an area, potentially improving the aesthetics of an urban environment. It takes into account the wider challenges of climate change and urbanisation, creating a long-term solution to water drainage, pollution, and environmental damage.

This can be seen by the four pillars of SuDS as set out in CIRIA C753 – The SuDS Manual 2015. These are:

1. Water Quantity - Controlling the quantity of runoff to support the management of flood risk and maintain and protect the natural water cycle.
2. Water Quality - Managing the quality of the runoff to prevent pollution.
3. Amenity - Creating and sustaining better places for people.
4. Biodiversity - Creating and sustaining better places for nature.

These pillars are the cornerstone of SuDS.

This may sound all well and good, but if it’s so amazing for the environment, why doesn’t every developer who can, use SuDS drainage?

Obviously, we provide SuDS design services so we’re a little bias towards SuDS drainage systems over traditional drainage systems for all developments, even small ones, but we’re definitely in the majority of businesses who believe SuDS is the way to go with any new development. However, in the interest of being completely open and honest we wanted to show you that there are a few negatives to be had with Sustainable Drainage options, so you can make a fully informed decision.

Firstly, let’s look at the main reason why people avoid SuDS – it can have a bigger initial expense.

The main issue with SuDS is who is ultimately responsible for the upkeep and inspection of the system once the development has been completed and is in operation.  A traditional pipe network will, provided it has been constructed to the appropriate standards, be adoptable by the sewer authority. It then become their responsibility.

However, some sewer authorities do not adopt SuDS. They argue that they form part of the land drainage and therefore they should not accept run-off from these features.  This is often at odds with the Local Council’s policy of providing SuDS. This can lead to development proposals becoming stalled between two stakeholders whose policies do not align.

Where surface water needs to be directed into the ground, due to good infiltration rates, this can impact the development proposals. This is due to the need under the Building Regulations Part H, to have all soakaways at least 5m from buildings, roads, and boundaries.

Secondly, The necessary technology to create the SuDS structures have additional costs to design and install it which tends to be more expensive than adding your development’s excess water to existing drainage infrastructure, particularly in urban areas.

Due to the way SuDS strategies work, there also needs to be a more in depth analysis of the local area in order to create a suitable design. This could include soil analysis, wildlife and ecology surveys, litter and silt removal plans, and a variety of other surveys that may be necessary. These all add up. However, creating a sustainable strategy and doing all of these surveys at the beginning of your project has been shown to mitigate bigger costs down the line if something comes up. So, it’s swings and roundabouts really.

Now, on to all the incredible benefits of using sustainable drainage strategies on your development!

There are tonnes of environmental benefits to using SuDs. SuDS is not just about removing water, but using that water for maximum benefits.

By using Sustainable Drainage, pollutants can be filtered from the excess water, sewage overflows can be prevented, flooding risk can be significantly reduced, and groundwater storage can be restored more effectively. This doesn’t just have an impact on the immediate development area, but can benefit society as a whole.

It can also be used to improve the aquatic ecosystems within the area and minimise any environmental and public impact your development may have (which is really useful if you’re looking to gain a BREEAM certification for your build).

In addition, where surface water is stored these areas can be repurposed into recreational spaces for sports and play areas, as well as providing a public space for people to enjoy.

If these benefits aren’t enough, then the increase in property values and housing saleability due to properties being located near open   might tempt you!

There are a variety of different SuDS options that are available to developers which all have different uses, as well as different locations in relation to the development or typical rainfall landing area.

There are three main distinctions for the types of SuDS available. These are; at source, site control, and regional control.

At source SuDS control water run-off at, or next to, where the rainfall lands on a surface. These are more likely what you’ll be looking at if you’re building houses. They include:

Site controlled SuDs cover the entire development site and tend to include larger scale methods mixed with the smaller scale products. They include:

• Detention basins – A depression covered with vegetation to hold rainfall and slowly drain it.
• Retention ponds – A larger depression which stores water, even during dry conditions.
• Wetlands – A vegetative area with shallow ponds and marshland.
• Swale
• Permeable paving
• Filter drains

Regional controlled SuDs can cover multiple developments within an area and tend to be on a much larger scale, draining to a particular body of water. They are:

• Detention basins
• Retention pond
• Wetlands

When you integrate SuDS (or any drainage, for that matter), it needs to be submitted to the planning authority that is local to your development.

It’s important to note that even when you’re working in low flood risk sites, many LPAs now insist that developers, architects, and planning consultants submit drainage assessments as well as flood risk assessments for any development. These should identify the impact of that site on any potential flood risk into the local watercourses.

The local planning authority (LPA) will manage the flood risk according to guidance set out in the National Planning Policy Framework. Each LPA tends to have their own published Flood Risk Policy as part of their local plan, which can be found on the specific areas of their website.

Most sites will need multiple solutions, so this is the point where a SuDS strategy designer will come in handy to make sure they integrate effectively with the overall development (hint: we do this! Click here to find out more about our SuDS design services).

When sending over your planning, LPAs will be looking for proposals that adopt the SuDS hierarchy. This is based on an ascending scale of sustainability with associated amenity and environmental benefits which you can see below.

When you work with a consultant SuDS designer, they’re the ones which will do the leg-work and speak to the LPAs and make sure your development is up to scratch and follows every guideline for quick planning approval. We would always recommend going with a consultancy who specialise in these, as they can get quite specific and there’s a lot of niche knowledge necessary to get this right so your planning goes through quickly (even if you don’t choose us, choose a specialist if you don’t have much experience in it yourself).

Whether you’re planning a small development, or a giant multi-use site, SuDS should be something you serious consider as more than just a drainage strategy.

Think about the greater impact of your project and the impact your business is having on not just the development site, but the area as a whole. It may not feel like your 5-bed development wouldn’t have much impact on the community, but you could great huge benefits to everyone around you if you considered the consequences in full.

You could also increase the resale value of your development and make them fly off the metaphorical shelves – so it’s really a win-win!

If you have anymore questions about the SuDS options for your development, feel free to contact our SuDS design expert Mark Naumann on [email protected] and he can help you understand all of your options and work with you to create a solution to solve all of your water drainage needs. We have a free quote policy, so there’s no obligation if we’re not the best fit for your development.