How to minimise stormwater pollutants and create a positive environmental impact with SuDS

Stormwater has always been a problem in highway design but since the roads now being built, or renovated, must last a long time it is wise to plan for future conditions - as far as they can be foreseen - rather than those of the past.

Increased rainfall, floods and storms all seem more probable than not with climate change, while the process of increased urbanisation—now evident the world over—will also increase the amount of stormwater that somewhere makes contact with a highway.

Demand for sustainable drainage systems (SuDS) will grow not just as an engineering solution to climate problems but as a result of public pressure on those who make political decisions on highways spending.

Society is becoming more conscious of climate change and environmental protection, and alarmed by pollution incidents. Spending on improvements for road traffic becomes increasingly contentious as a result, and the argument for highways spending will be hindered if linked to incidents of pollution from chemicals in runoff from roads.

Across the UK, indeed some other countries too, highways must compete with services like schools and older people’s social care for scarce funds - it cannot afford to become politically unpopular because of a poor pollution record.

Avoiding stormwater-related issues

There are plenty of examples of stormwater pollutants and the damage they do. Some, such as sediment, may not seem dangerous in themselves, but can reduce the amount of light in the water available for plant growth, decreasing the supply of food for other organisms. They can also damage fish and suffocate organisms that live in lakes and watercourses.

Heavy metals from vehicle wear, sewer overflows and spillages can poison living organisms and persist in the environment for a long time, while microorganisms from sewer overflows may be injurious to human health.

A blog published last year on the Earth Institute section of Columba University described the practical impact of runoff pollution. It said runoff is ‘incredibly good at picking up whatever it comes into contact with as it travels downward to the lowest elevation, dirt, nutrients, trash; stormwater does not discriminate’.

The blog added: “When water has no way to enter the ground, it will keep travelling above ground until it hits the nearest river, lake, or sea. Since this water had no opportunity to deposit whatever it grabbed along the way, it deposits that matter into the water body, where it can begin to have negative effects on the ecosystem.”

So how does it work?

SuDS systems store or reuse surface water by decreasing flow rates to watercourses and improving water quality. They work by using a sequence of source control, pre-treatment steps, retention systems and infiltration systems. As surface water flows through the SuDS systems, flow velocity is controlled and pollutants are removed. 

Source control decreases the volume of water entering the watercourse by intercepting run-off water for subsequent re-use—for example for irrigation—or for storage and later evaporation.

Pre-treatment ditches, filter trenches or hydrodynamic separators will remove pollutants from surface water prior to discharge to watercourses or aquifers. Retention and attenuation systems delay the discharge of surface water to watercourses by providing storage within ponds, while infiltration systems manage water soaking into the ground.

Using SuDS is accepted as a best practice in highway projects to prevent runoff pollution and flooding. SuDS are also a low impact solution - they do not involve costly, unsightly or unsustainable large infrastructure. They may also be used when housing is built with local access roads in areas prone to flooding, when such construction might be inadvisable without a SuDS system to carry water away effectively and safely.

Stormwater capture need not be a burdensome extra to good highway design but rather something that gives a positive environmental impact and will meet client and public demands.

Products such as Stormbloc® Optimum, available to engineers in the United Kingdom and Ireland, attenuate surface water and stormwater effectively even in challenging high-traffic urban environments. It is a modular and easily customisable way to manage water, giving engineers the freedom to configure storage for even the most challenging SuDS project.

Stormbloc® Optimum is a resilient geocellular storage system that provides underground storage and infiltration of urban runoff. Lightweight materials combined with robust design make it easy to transport, quick to install and durable, even beneath place with heavy traffic such as roads, car parks and warehouse yards.

A review in January 2019 of SuDS delivery by flood authorities—sponsored by the Chartered Institution of Wastes Management—found implementation was inconsistent between authorities given the lack of national policy.

The report argued it was essential to ‘counter the belief that changes to SuDS policy would prevent or significantly delay the delivery of housing; and the belief that short-term economic priorities outweigh the need for long-term planning and adaptation to the changing weather patterns that create surface water flooding’.

Hydro International stands ready to help those who have adopted this new thinking on dealing with storm water and its consequences.