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5 reasons to promote sustainable drainage systems (SuDS)

SuDS are rainwater drainage systems designed to mimic the natural environment by managing rainwater at source, attenuating flows and encouraging infiltration. They often include planting and can help remove pollutants from rainwater. One example you may have heard of is the raingarden. Other examples are swales, ponds, green roofs, infiltration basins, permeable paving, filter drains.

1. Reduced flood risk

Flooding devastates communities. The incorporation of SuDS to new and existing developments is a critical part of the solution to prevent future flooding.

aftermath of flooding

The aftermath of flooding

Before humans arrived and developed towns and cities, the natural landscape was green. Rainfall hitting the land would infiltrate, soaking through the soils and joining the groundwater below. Once the upper soil becomes fully saturated, water would flow overland, finding its way to watercourses or waterbodies (this is where the term greenfield runoff comes from).

SuDS mimic the behaviour of the natural landscape, encouraging infiltration and slowing down the flow of rainwater to sewer systems or watercourses downstream. This helps mitigate against ‘flash floods’ which occur when rainwater from roofs and paved surfaces are piped directly to public sewers and watercourses, overwhelming them and causing flooding.

SuDs can also provide storage. Outflows can then be restricted, holding back water onsite and releasing it at a slower, more manageable rate.

2. Enhance biodiversity

For the city dwellers, have you ever found yourself in a quiet moment in your city or town and noticed how much you appreciate the simple things, like the sounds of bird song? The leaves of a tree blowing in the wind or the sight of a squirrel hopping across a footpath? It’s widely recognised that wildlife and nature bring people happiness.

The problem is, at the time many cities were built they didn’t consider wildlife and nature, other than the odd park perhaps. And, in todays society wildlife and biodiversity still aren’t prioritised in new development, they’re just an annoying planning constraint or an afterthought. That planning constraint, however, is soon to become much more regimented with the introduction of the Biodiversity Net Gain (BNG) policy which will apply to developments from November 2023. I'll write more about that in another post.

So, what if I told you that you could introduce biodiversity and encourage wildlife to your project through sustainable drainage design. You need drainage anyway. Instead of endless manhole covers and gullies, why not create something more natural. A habitat. SuDS can transform a space into something functional that brings people happiness. All the while, reducing the embodied carbon of the development and enhancing biodiversity.

suds biodiversity

Butterflies and Bees thriving in a biodiverse habitat

3. Bring back green

Grey might be in fashion for your new kitchen or bathroom, but in the streets the constant greys are drab and depressing. We need to bring green back to cities to bring them to life, literally.

One of the key objectives of SuDS is the integration of drainage and landscaping, creating a hydraulically connected landscape and providing a multitude of sustainability, biodiversity and amenity benefits in the process.

Thriving soft landscapes within built up areas means more amenity, better air quality and a cooler city microclimate.

We need more SuDS and urban greening to untwine the hundreds of years of sprawling grey mass that’s been created. Years ago, we didn’t know any better. Now we do and we can do things better, greener.


Raingarden SuDS in South London

4. Improve air and water quality

Have you ever noticed that burning, metallic, exhaust smell walking down your local high street and thought ‘I definitely need to move’? You can almost taste it. It’s the flavour of self destruction.

SuDS can help us with the issue.

SuDS such as rain gardens, green roofs and swales, allow rainfall to permeate through layers of soil, sand and stone. This filtration traps and encourages the breakdown of pollutants that would otherwise lead to contamination downstream.

The root action of plants can help remove pollutants from the soil, whilst leaves are able to trap airborne pollutants as well as create physical barriers to both particle and noise pollution. Vegetation takes in carbon dioxide and releases oxygen, the very gas that gives us life. Evapotranspiration helps reduce the urban heat island effect, cooling us down.

rooftop planters

Rooftop plants - planters like these can be integrated with shallower green or/and blue roof systems

5. Legal changes are coming

Changes to the Flood and Water Management Act 2010 are proposed by the Government for 2024.

The results of a Government review published 10 January 2023 recommend making SuDS mandatory on all new developments in England, through the implementation of Schedule 3 to the current legislation. Schedule 3 allows for new approval and adoption processes involving a sustainable drainage system approving body and conditions the right to connect surface water drainage to the public sewer upon the system being approved.

This means a higher quality and quantity of SuDS will be expected in the future and design details will have to provide sufficient detail to obtain approval.

So, to conclude:

Green SuDS can reduce flood risk, reduce pollution and provide wildlife habitats, contributing to an overall stronger ecosystem and happier, healthier cities.

In the cities of today, our mental and physical health are suffering. That’s why we need more SuDS in the cities of tomorrow.

If you need creative, expert and cost effective sustainable drainage design, we are here to help.


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