What are Sustainable Drainage Systems?

What are Sustainable Drainage Systems and how do they work?

The term Sustainable Drainage Systems covers a wide range of projects, but they are all designed to achieve one goal - slow the flow of rainfall through our urban landscapes, preventing damaging floods.

There are a number of ways that this water management can be done, all the way from green roofs through to underground water storage systems. We will go over the most common implementations below, but if you’d rather watch a video then this is an excellent introduction:

Green Roofs

Green roofs are exactly what they sound like - a roof which is covered in a growing medium and vegetation. They can retain an astonishing 75% of rainfall, releasing it back to the atmosphere via slow transpiration. Green roofs have the added benefit of providing a habitat for wildlife - particularly pollinators such as bees and butterflies.

Rain Gardens

Rain gardens are very similar to green roofs, but can be installed anywhere - with usual locations including patios, driveways and paths. The rain garden soaks up the water when it’s wet and then slowly drain away once the rainfall stops. The added benefit of rain gardens is the fact that they really uplift the aesthetic of an area, with beautiful flowers and plants.


Swales are essentially more basic rain gardens, typically found on road verges. They are a shallow and wide depression, typically planted with grass. These are typically lower maintenance, while still having a positive impact on rain water storage and pollutant removal.

Permeable Paving

Permeable paving looks identical to normal paving, but has the key advantage of letting water drain through it rather than running off into nearby drains. They often filter the water during this process, helping remove physical pollutants. They work best when installed in areas with lighter vehicular traffic, such as cycle lanes or hard shoulders.

Rainwater Harvesting

A rainwater harvesting system will collect rainfall from roofs and pipe it into a storage system, where it can then be used directly for non potable purposes, such as watering your garden. Some people decide to go one step further and filter the water, letting them drastically reduce their mains water usage.

Retention Ponds

A retention pond doesn’t reduce surface runoff, but it does direct it into a safe place where it can be stored and treated before being released back into the system. They are typically planted with a range of aquatic vegetation, such as reeds, which both aid filtration but also provide a habitat for wildlife.


Wetlands are natures version of a “retention pond” - an area of land permanently or frequently covered in water and highly planted with aquatic vegetation. They are some of the most threatened habitats globally, and a crucial habitat for some of the world’s most intricate ecosystems. The UK wetlands are especially rich in birdlife and a crucial stopover for many migratory species.

Maps Guide

Want to explore these locations yourself? Download a free Greenprint guide to explore urban sustainability sites in the city you call home!

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Why are Sustainable Urban Drainage Systems so Important?

There are two big reasons why SuDs are becoming increasingly important in today’s urban landscapes. First, the rainfall pressure on our cities has increased and looks to continue to do so. Secondly, the monetary cost of each flooding event is also increasing.

Increased rainfall pressure

Climate Change increases the extremes of our weather. We get drier summers, but wetter winters - with a specific increase in the extreme downpour events. In July 2021 over 40mm of rain fell in just three hours at Kew Gardens in London, flooding the tube and other key infrastructure. This is a trend that is set to continue and worsen with time, as shown by this Met Office analysis.

Met Office data highlights just how extreme our rainfall events are becoming

Increased impact

As our major urban areas are continually developed, and flood plains encroached upon, the economic costs of each flooding event is magnified. The floods of 2015/16 cost an estimated £1.6bn. The highest portion of this cost (32%) was incurred by businesses, with residential properties (21.9%) and infrastructure (21.3%) being equally hard hit.

Who is Responsible for Sustainable Urban Drainage Systems?

SuDs can be installed on both public and private land, with the responsibility for the SuD being decided during the development process. From 2024, new national legislation makes it likely that nearly all new developments will require the installation of SuDs.

Who designs Sustainable Urban Drainage Systems?

There are a number of private organisations who specialise in the installation of SuDs, and ensure that they meet the Environmental Agency standards. A quick google will help you identify your local suppliers. For certain applications (such as installations at schools) there are even grants available to accelerate implementation. On public land, the Local Authority will typically coordinate the subcontracting of these organisations.

How can I support the implementation of SuDs?

You've already made a great start in creating a positive future by simply taking the time to learn more about SuDs, and the next stage is to get out there and visit them! We would recommend downloading our Greenprints guide to help you find your local SuDs (see above for the link).

If you can, then providing funding to the organisations implementing SuDs can make a huge difference. Alo Mundus makes this process easy and if you are a business we can even coordinate engagement days for your staff - from helping tend to the vegetation to keeping them clean and tidy. Simply discover projects by clicking the link below.

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