Sustainable Drainage Systems in Action

 In Gardening, Landscaping, Urban Gardening

Sustainable Drainage Systems in action are increasingly appearing in the UK.

But to my mind they are not appearing nearly fast enough!



What are Sustainable Drainage Systems?

Often abbreviated to SuDS, Sustainable Drainage Systems are structures that slow down water run-off.

They slow rainwater and give it a chance to sink into the ground. That is instead of it rushing to the lowest point and causing flooding.

The implementation of SuDS can also offer improved water quality, better biodiversity and also an amenity.

So not only can we reduce flood risk but we can also reduce pollution and improve the environment for plants and for wildlife.

SuDS are sometimes referred to as rain gardens and that’s because plants play a key part in their success.



Climate Change and Storms

There is no doubt that our climate is changing.

soil erosion, drains, roadside

Severe soil erosion

Weather is becoming more difficult to predict. We’re getting more frequent and more severe storms.

Coupled with urban expansion and impermeable surfaces in our built environment we have to find a better way of managing rainwater runoff!

I believe that sustainable drainage systems and ‘rainwater gardens’ in particular could be one of the main ways that we do this.

SuDS need to be part of a package of controlling rainwater runoff and are not the only solution but they are a very important solution.





Retro-fitted SuDS

SuDS by road, sustainable drainage system, rain garden

SuDS retro-fitted to roadside

It seems to me that designing solutions into new build developments alone will not be enough to solve this problem.

We need to retro-fit sustainable drainage systems into our existing built environment.

So where there is space, instead of having bare earth, grass or tarmac between our pavements and roads, we need SuDS there instead.

Do compare the eroded road verge image above with this planted one. The positive effect can clearly be seen!

This image is taken in early January in Portland, Oregon and so the plants perhaps do not look at their best.

The wooden barriers impede the flow of heavy rain slowing it enough to allow some to drain into the soil. When the plants are actively growing they will use some of that water too. But their physical presence slows runoff and filters out solids carried in the rainwater.

Of course, plants are not only there to slow down and filter the water, they will benefit wildlife too.

This roadside sustainable drainage system is part of many that line this sloping road. Surplus water flows from one unit into the next.  And so on down the street. If water levels rise too high and risk flooding the road then there is a raised outfall in each that allows excess water to go into the main drain. The object is not to stop the runoff but to slow it down so that it has a chance to filter into the soil below.

It occurs to me that where we have alternate road calming islands on our roads these could easily be SuDS. Where we have pedestrianized streets we could easily have rainwater gardens!


Planned SuDS from the get-go!

a new SuDS system in a modern building, rainwater garden, plants, Sustainable drainage systems in action

SuDS system for a modern building

New developments must have rainwater management planned in at the outset.

SuDS needs to be an integral part of the plan!

My image here [again in Portland] illustrates how a rainwater garden has been incorporated into a new build. This building had a typically high degree of hard surfaces surrounding it. So rainwater could not sink into the ground. This is typical of most new builds. Here the runoff water was gathered and fed through a series of planted SuDS.

The rainwater has to snake through each level before ending up at the lowest.

If it hasn’t already soaked into the soil, it then flows into an overflow drain.

Much of the water will have disappeared by then.





What plants are suitable

With an emphasis towards using native plants, the plant variety choice is important. But the good news is that many plants will thrive in a sustainable drainage system.

Plants chosen must be able to tolerate variable water levels. They must tolerate regular flooding and be well rooted. But they also need to put up with periods with little or no rain.

Native plants are best adapted to do this. They will also offer the best opportunity to boost insects, birds and other wildlife.

Plants likely to succeed best are grasses, rushes, reeds, sedge. So Carex, Cyperus, Glycera, Phalaris and Phragmities are likely to cope with what can be quite demanding conditions.

But some shrubs are very tough and would work too. So Spiraea, Symphoricarpos, dogwoods and dwarf willows are likely to grow and filter rainwater well.

Often forgotten among plant selection, some ferns would be a good addition to the plant mix. Athyrum, MatteuciaOnolea and Osmunda. These add structure and texture and are very trouble free to grow. Incidentally, I’ve written a blog on hardy ferns here.

Where more colour is needed then plants such as purple loosestrife [Lythrum], Iris and Hemerocallis should be considered. Rain gardens can be showy if careful thought is given to the plant selection. Improved selections of native or near native species will offer an improved aesthetic value.



Nature reserves too

SuDS can also be nature reserves too!

Sustainable Drainage Systems in action

Sustainable drainage system/wildlife reserve

Portland in Oregon has many examples of Sustainable Drainage Systems in action.

On a recent visit I noted several that doubled up as nature reserves.

Securely fenced off and invariable abutting woodland, these areas controlled runoff water and provided good habitat for wildlife.

Sustainable Drainage Systems in action

SuDS behind housing


Here is an example of how SuDS can be incorporated in housing. This wraps around properties, links to woodland and offers a valuable wildlife environment.






Sustainable Drainage Systems in action, sign

Sign explaining how SuDS filters water

Sustainable Drainage Systems in action, roadside

SuDS showing overflow outlet

Sustainable Drainage Systems in action

Sustainable Drainage Systems in action

Sustainable Drainage Systems in action

Road drainage captured by drain fed into SuDS.




Additional reading

Susdrain is a great organisation to learn more.

To quote from their excellent website I think this sums them and their aims up ~ “Susdrain is a community that provides a range of resources for those involved in delivering sustainable drainage systems (SuDS). SuDS help to manage flood risk and water quality and also improve biodiversity and amenity as well as a host of other benefits to create great places to live, work and play.”

Find out more about Susdrain here.


More to see in Portland

If you visit Portland in Oregon there are some great gardens in and around the city.

The Portland International Rose Test Garden is fabulous in summer. More details of the rose garden here.

It’s in Washington Park where you will find probably the best Japanese garden outside of Japan. I’ve written a blog about a recent visit here.

Downtown in Portland you’ll see SuDS in the streets but do make time to visit the Lan Su Chinese Garden there. I’ve written about my visit to this great garden here.



Do you have a sustainable drainage system near you? I’d be fascinated to hear about it.

Finally I’d like to acknowledge the input into this blog by water scientist and fellow garden expert Janet Manning.



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Showing 2 comments
  • Janet

    Hi Alan,
    Its great to get the horticulture and landscape industry starting to talk more about SuDs. Not all SuDs systems are created equal and some are still installed that have no plants or soil involved, but they simply collect rain and discharge it to a drainage system at a slower rate. That achieves the reduction in flood risk but, by missing out on plants and soil being able to receive the rainwater we are missing out on opportunities to improve the water quality, biodiversity and amenity value that these systems could be providing. It’s an opportunity for horticulture to show how plants and soil are beneficial to repairing the water cycle rather than being water consumers. Matching the right plants to the soil texture and climate extremes is the key to good design, we need to be working with the environment and climate we have, rather than changing the conditions to grow the plants we like to look at. Look out for the Defra consultation on a SuDs approval body and adoption due later this year.
    Many thanks for raising this.

    • Alan Down

      Janet – thank you for making very valid points and adding to the conversation! I do feel that we could do so much better in the UK and always come back inspired from what I see when visiting Portland. I do hope that plants play a big part in the Defra proposals later this year. Alan

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The Japanese Garden in Portland