In Focus: Sustainable Drainage Systems (SuDS) - What it means and how they work

CLA Land Use Policy Adviser Alice Green answers key questions surrounding SuDS. Find out how members can benefit from the CLA’s expert advice
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Most landowners will have seen the term SuDS growing in popularity in recent years, particularly in the urban development landscape, but SuDS are equally as important to those in rural land ownership. But what exactly are SuDS?

Put simply, Sustainable Drainage Systems, known as SuDS, are a variety of water management tools designed to prevent flooding and improve water quality and biodiversity by slowing run-off into sewers, drains and watercourses.

Following the review into the devastating floods in 2007, SuDS were identified as a central tool to prevent flooding. In 2019, SuDS were then listed as one of the five key considerations for development under the National Planning Policy Framework when managing flood risk. This puts SuDS at the centre of good development and for protecting people and the environment.

For rural landowners, this means SuDS must be a key consideration for any plans you have for developments whether that be selling land to developers or constructing your own properties or farm and equestrian structures. They are equally as important for preventing run-off of pollutants and soil into watercourses in areas at risk of the issue.

While there is a cost associated with SuDS, there are also a raft of benefits for landowners. Not only do they cut the risk of flooding, but they also help prevent leaching and the loss of soil nutrients by slowing run-off from your land. As a result, you improve the quality of water entering rivers, streams and the sewerage system and also help to increase biodiversity. Plus, this can be done without any significant loss of agricultural land.

In this blog, I’ll look at SuDS in more detail, exploring the benefits, the types of SuDS and any key considerations for rural landowners.

Why do we need SuDS?

With any new development, you are generating lots of hard surfaces from roofs and driveways to roads and car parks. All of these hard surfaces prevent water from being soaked into the ground. By taking away these permeable areas, the run-off from the hard surfaces is significantly higher than the equivalent greenfield area.

Traditionally, run-off from buildings and other hard surfaces was directed straight into the sewers. And, with older systems, this relatively clean rainwater is directed straight into the combined sewer network. This can result in the system being overwhelmed and triggering flooding incidents.

For example, an average three-bedroomed house has a roof with a surface area of 70 square metres. If you take an average monthly rainfall of 76.7mm for the UK, this means the roof is directing 5,320 litres of water into the drains each month. If you add in the average two-car drive attached to the house, this will put another 3,380 litres into the sewer network. That’s more than eight tonnes of water a month added to a system that is already under considerable strain. When you start to add in the associated roads and other impermeable surfaces, it adds up to a considerable amount of water.

Couple this with the need to build thousands more homes and the ongoing impact of climate change, which is generating wetter winters and an increase in storm events, and it spells disaster for our drainage systems, rivers and streams.

When a flood happens, the mixture of clean rainwater and dirty foul water in the sewer system spills out of the network and causes damage to homes, businesses and land.

In the rural landscape, heavy rainfall can also cause run-off from fields increasing the risk of contaminating watercourses.

These are the issues that SuDS aim to address. By creating a network of sustainable drainage systems that slow the run-off, it ensures more water is absorbed into the ground, any sediment is allowed to settle back into the ground, and pollutants are broken down, improving water quality and reducing the threat of contamination.

What are SuDS?

Essentially, SuDS are systems designed to slow water down. They are a network of natural structures such as grassed swales, retention ponds, wetlands, soakaways and sediment traps.

These systems are often used in various combinations to give water the chance to soak into the ground and allow particles to settle out of the rainwater run-off. This improves water quality, prevents flooding and protects the local environment and watercourses.

Traditional systems both in urban and rural landscapes were designed to carry rainwater away quickly and this meant they transferred large volumes of water to watercourses and sewers, along with any pollutants and sediments.

With SuDS, they temporarily hold the water, and this ensures soil and nutrients aren’t washed away in agricultural settings and water is also driven downwards, recharging aquifers.

As an added bonus, the SuDS create rich micro-wetlands for wildlife and help boost biodiversity.

SuDS can also be created with minimum loss of agricultural production and the Environment Agency argues that SuDS can make existing systems like buffer strips, walls and hedgerows even more effective.

What are the types of SuDS?

SuDS are designed to mimic natural structures and either slow water down, hold it or encourage water to soak into the ground. A variety of the different types of SuDS are often used together to manage the water effectively to remove particles and pollutants and slow water down to prevent flooding.

Swale

Grassed swales are wide, shallow ditches that are often planted to slow the water down and allow particles to settle, improving water quality.

Sediment traps

These are a temporary containment area where rainwater run-off can be captured so any sediment can be allowed to settle. When the sediment is settled, the clean water is usually then discharged into another SuDS, typically a retention pond.

Retention pond

This is a simply a pond where water can be stored before being allowed to enter a watercourse at a managed rate or soak away into the surrounding land. An additional benefit - aside from the biodiversity benefits - of retention ponds that this again allows any sediment or particles to settle and increases water quality.

Detention Basins

Unlike retention ponds, detention basins may not always hold water and are designed to fill during rainfall to allow the water to soak away into the ground or be discharged into other systems in a managed way when the water quality has improved.

Constructed Farm Wetland

These are large shallow ponds, or a network of ponds that are heavily planted and take the run-off and hold the water while sediment settles and any pollutants are removed by the plants or through breakdown in the soil. Again, these can be valuable wildlife habitats.

Green roofs

These are specifically for new structures and are sometimes known as ‘living roofs’. This is a roof featuring a variety of plants that absorb rainwater and also slow any run-off. They can reduce run-off by up to 80% and are capable of absorbing 5mm of rain at a time.

The types, size and number of measures will obviously vary depending on the nature of the land or development but can be extremely effective when used together with careful planning.

What are the challenges of sustainable drainage systems?

While there are many benefits for SuDS, there are obviously some challenges associated with adopting the systems. The first is that SuDS can be more expensive to incorporate into your drainage plans than the traditional systems.

That said, most water companies are keen for landowners and developers to adopt SuDS systems and they offer a range of funding packages and incentives so it’s worth checking with your local provider.

Another challenge of SuDS is the maintenance of these systems. They do need some work to maintain and manage and some sewer authorities will not adopt SuDS. With most developments, when the traditional pipework has been installed to the appropriate standard, the sewer network will then adopt it and it then becomes their responsibility.

With SuDS, it forms part of the land drainage and, as such, it doesn’t necessarily fall under their authority. While SuDS take little maintenance, it could be your responsibility to maintain and manage.

Developing an appropriate SuDS strategy will also cost money as you may need a variety of surveys to understand what will be the best system for you. However, creating a well-designed, sustainable system will deliver benefits in time.

Key considerations for SuDS

If you are considering any development work, there are certain requirements around SuDS and it is worth seeking specialist advice before pushing ahead with plans. Similarly, if you have land where run-off into watercourses could be an issue, again SuDS should be considered.

In this situation it is again worth seeking specialist advice and exploring surveys to identify the best solutions for your land to ensure you create the most effective and efficient system. This will ensure any SuDS are effective and sustainable while also impacting the least on your land and requiring the minimum amount of management and maintenance.

As I’ve said, there are a number of schemes and incentives that can be applied to SuDS which can help cover costs and deliver expert guidance.

It is key to remember that SuDS are just one element of the approach to managing run-off, lowering flood risk and increasing water absorption. They offer a wide range of benefits to landowners but need to be part of a wider strategy so always seek advice on these schemes.

CLA is able to provide a range of expert advice in water management, planning, environmental enhancements and habitat restoration so, speak to your CLA representative for guidance if you are considering creating your own SuDS schemes and they will be happy to answer any questions you have.

Key contact:

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Alice Green Land Use Policy Adviser – Climate and Water