Sustainable Drainage and Highways

Posted on 14 November 2019 by Sarah Netherclift

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This article features in GreenBlue Urban's Guide to Urban Trees, Highways and Utilities. 

Unlocking New Solutions to Old Problems 

Designing drainage solutions presents its own set of challenges for highways engineers. These centre around safety, stability and pollution as carriageways have to be kept clear of surface water asap to avoid flooding and aquaplaning. Engineers are keen to pipe water away to avoid the risk of water affecting the road’s foundation, and pollution from the road surface – oil, rubber, metals, microplastics, etc. – must be prevented from entering rivers and streams.

While engineers may be inclined to use traditional piped drainage on highways, carefully designed sustainable drainage systems (SuDS) can match the quantity and quality requirements of traditional drainage and add amenity and environmental value as well.

Living and driving safely with SuDS

The amenity value of SuDS is usually associated with residential areas rather than main carriageways. Rain gardens and tree pits along residential roads reduce the volume and velocity of runoff and add considerably to biodiversity and environmental impact of an area. They can also perform a useful traffic calming function. Along major carriageways, amenity may be less of a consideration but it really shouldn’t be. Incorporating landscaping and trees in a highways design plays a role in noise reduction and improving air quality, for example.

Implementing sustainable drainage into highways design requires a slight shift in thinking for highways engineers. We say ‘slight’ because designing SuDS uses the same underlying principles of hydrology and hydraulics as conventional drainage. It just involves applying them in a way that includes amenity, biodiversity and environmental considerations.

Evolved thinking and design software

To accommodate demands for a more sustainable approach to highways drainage, MicroDrainage drainage design software from Innovyze has evolved in ways that allow highways engineers to address the challenges. Take water quality; pollutants tend to build up on a collection area – in this case a road – and are washed off with rainwater runoff. When rainwater runs through sustainable drainage systems in the treatment train, pollutants can be removed by various natural processes. The MDSuDS module available in the MicroDrainage solution allows you to calculate pollutant washoff and removal rates through different SuDS structures. This helps designers evaluate the most appropriate sustainable drainage practices for reducing pollutant runoff into receiving water courses.

Of course, it is important to test the capacity of any design to handle runoff and reduce the risk of flooding under different rainfall conditions. For main roads and motorways, the SuDS structures are often likely to be long, linear features like swales or trenches. Point inflows at the top and bottom of a section of a SuDS structure can put too much water into a small location. Lateral inflows from the carriageway means that water flows incrementally into the drainage structure and can be designed to be deeper at one end and fill up gradually. Again, the performance of lateral inflows from the carriageway to the SuDS feature can be assessed in MDSuDS.

The drainage design capability of MicroDrainage has long been recognised as an industry leader, not just for standard drainage but for enabling innovative solutions to traditional problems.

For more information take a look at our Drainage Design Solutions pages

To download GreenBlue Urban's report, visit: https://www.greenblue.com/gb/resource-centre/urban-trees-highways-utilities/

 

 

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