Sustainable Urban Drainage Systems: What Are They, How They Work + Benefits

Sustainable urban drainage systems title

My local area has just been landscaped with a sustainable urban drainage system.

Not familiar with the term? No, neither was I.

I wanted to find out what sustainable urban drainage systems are all about, how they work and the benefits they bring to both the environment and local area..

Straight away, the benefits of this nature-based solution were very clear to me.

The sustainable drainage system has been created on what was previous a plain old patch of grass, without much use and very prone to waterlogging.

The two next pictures below show the area in the winter time and then once established in the summer. As you can see, the area has a good circular path, new trees, wetland planting, a new wildflower meadow and a little marshy moat where the rainwater collects. From my experience, it’s a vast, vast improvement.

Let’s take a closer look at sustainable drainage systems.  

sustainable urban drainage system dales brow
SuDS in Dales Brow, Greater Manchester, February 2021

What are Sustainable Urban Drainage Systems?

For many people, an urban environment means concrete, cars and lots of buildings. Urban cityscapes don’t often have much room for nature and greenery.

Replacing the greenery and natural spaces are a lot of hard, unnatural surfaces. Unsurprisingly, these aren’t very good at soaking up rainfall and water. Factor this into a rainy place like Manchester, and you have a bit of an infrastructural problem that puts a lot of stress onto the drainage system.  

Sustainable Urban Drainage Systems, or just Sustainable Drainage Systems (both referred to as SuDS here) aim to improve the local area for people and the environment by dealing with surface water with a nature-based solution.

The SuDS philosophy is to replicate what would have been the natural drainage before a site was developed and urbanised.

As the name suggests, SuDS offer a sustainable and long-term solution to manage surface water.

There are four pillars of sustainable drainage system design:

  1. Water Quantity – limit the flood risk and protect the natural water cycle
  2. Water Quality – manage the quality of water run off to limit pollution
  3. Amenity – create a better area for local residents
  4. Biodiversity – create a better area and enhanced habitats for plants and animals
sustainable urban drainage system SUDS dales brow
SuDS in Dales Brow, Greater Manchester, August 2021

How do sustainable urban drainage systems work?

Sustainable urban drainage systems ultimately work by slowing down surface water run-off.

SuDS can reduce water flow rate with a number of different techniques. A well-designed SuDS system does this through one or a combination of:

  • Shallow channels and natural ditches (bio-swales) that can convert to wetlands
  • Infiltration systems, such as trenches and soakaways
  • Water retention areas such as ponds and basins
  • Natural flow control restrictions, such as boulders, planting and check dams

The system of ditches, boulders and planting slows the flow of water. This allows more time for the surface water to either soak into the ground and soil (where it either slowly drains away to the groundwater source or gets absorbed by plant roots) or evaporate off the vegetation and into the air.

Not all the surface water soaks into the ground or evaporates away. The remaining, reduced volume of water, which has now been naturally filtered, gets slowly released into a nearby water course, such as the brook near my home, or to recharge groundwater storage.

After all, this is how nature would have handled water before the area was urbanised.

What this does it help to prevent flood risk downstream.

dales brow before
Dales Brow before the sustainable drainage system

What are the different types of SuDS?

There are broadly three different types of SuDS systems.

  • Filter strips, shallow channels and ditches (swales)
  • Wetland area – marshland and basins
  • Water storage facilities – such as ponds

Depending on the type of area that needs transforming, different SuDS systems can be combined.

For example, the new SuDS near me is a combination of shallow channels and the creation of a temporary wetland area.

suds wetland drainage area
Temporary wetland area of the SuDS

What are the benefits of sustainable urban drainage systems?

SuDS offer many benefits to the local area, people and nature.

For this reason, they are considered an excellent environmental and eco-friendly choice for managing rainfall and surface water.

The benefits of sustainable urban drainage systems include:

  • Creating a nature-based solution to the benefit of the environment
  • Creation a multifunctional area
  • Managing water run-off and reduce the chance of flooding in urban areas by encouraging the natural soaking of water into the ground
  • Improving water quality through biofiltration, which decreases the chance of pollutants being washed into rivers and groundwater
  • Attracting wildlife and improving biodiversity
  • Increasing carbon storage
  • Improvement of air quality
  • Education opportunities – get local schools involved

According to the research and evidence presented on Greater Manchester Green City, SuDS can help tackle climate change by soaking up 0.2-0.3kg of carbon per m2 per year and storing 1.6-5kg of carbon per m2 – a wetland area can store significantly more.

The main disadvantage to the creation of more SuDS is cost. Although we are only trying to replicate the nature-based solution that was there before, it costs a lot of money to undo our rampant urbanisation.

The benefits of creating sustainable drainage systems are so substantial (in my view) that it’s a no-brainer that they should be included on all new development sites and retrofitted where possible.

SUDS deans brook watercourse
Behind in the trees in the above images, the SuDS runs down to this brook

When were SuDS introduced?

Urban drainage dates back thousands of years, but the idea of sustainable urban drainage systems is relatively new.

The area of SuDS has experienced a growth in interest since the late 1990s as understanding of the negative environmental aspects of urban development has increased.

The growth in popularity of sustainable drainage systems also comes at a time when cities and urban areas are actively looking for solutions to reduce CO2 emissions and increase environmental sustainability. 

For example, in Greater Manchester the IGNITION project has been created to help the region adapt to the impacts of climate change through nature-based solutions.

My local area example: Sustainable Urban Drainage System at Dales Brow, Salford

In a partnership between City of Trees, the Environment Agency and Salford City Council, a sustainable urban drainage system was created at Dales Brow in Swinton. The land here previously was prone to flooding and brought very little value to the area. Essentially, it was a patch of grass.

It really has been a terrific transformation into a new 64 square metre wetland area with tree planting, a wildflower meadow and lots of plants.

The new wetland area now means that the flow of rainfall running along the surface is greatly reduced and has a chance to be naturally biofiltered. This helps remove and breakdown pollutants into harmless compounds that eventually get fed back into the nearby brook.

It almost goes without saying, but this new patch of biodiverse habitat is so much more beneficial to the environment and people who use it – like me and Murphy on our morning walks.

For the cost of £127,000, I think this is well-worth the investment.

sustainable urban drainage system greater manchester
SuDS benefitting people, wildlife and the environment

All the evidence suggests that sustainable urban drainage systems can transform low quality areas of our towns and cities into high quality, valuable assets.

Not only can SuDS do their primary job of soaking up rainfall and preventing flooding, but they offer a wide range of extra benefits that will help tackle climate change, improve the lives of local people and help restore the habitats of wildlife and improve biodiversity.

SuDS offer part of the solution to help urban areas become more sustainable. To me, this is what sustainability is all about. A simple solution that works for both people and the environment.


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