Sustainable drainage systems: re-engineering urban landscapes to manage runoff
24 October 2017
We are surrounded by numerous examples where the landscape does not provide any tangible management of rainfall, and runoff is quickly conveyed underground into pipes that can quickly become surcharged, writes Anthony McCloy
Australia Road Park, in London
The recent Australia Road SuDS Park in London exemplifies an integrated design approach to deliver a successful green and social community ‘oasis’ that both protects against flooding and significantly reduces the volume of storm runoff from the site to be treated at the wastewater treatment works.
If both engineer and architect work in unison, the benefits of more flood-resilient landscapes that offer improved functionality and attractive surroundings for the community, all at reduced construction cost, are easily attainable. A recent example of this type of joined-up thinking is the delivery of the Australia Road scheme in the White City area of north-west London.
Whilst the initial focus of the scheme was urban regeneration, the client quickly realised that redevelopment was an ideal opportunity to introduce sustainable drainage systems (SuDS) as part of an integrated landscape within the Borough.
In this way, SuDS can be viewed as an asset to enhance the character of the landscape/scheme rather than storing runoff out of sight in an underground tank which would have provided no other benefits other than storage of runoff.
The notion that water has a valid place in the landscape (even in densely populated areas of London) was emphasised at the first stakeholders’ meeting. The head of the residents’ committee outlined his vision for the scheme as “the creation of an urban oasis”, which would draw people in and create a social hub for the local community.
Notably, health and safety in relation to open water – regardless how temporary or shallow – was not raised as a key concern.
Designing for the ‘host community’
With the mission statement enshrined, McCloy Consulting and Robert Bray Associates set about designing a space that tells the story of water in the landscape by mimicking drainage in the natural catchment. Space was designed to be shared and enjoyed by users of the adjacent school and playgrounds, as well as the wider community. This was a fundamental design driver, as the scheme lies between the school and playgrounds at the heart of the White City estate.
This presented the opportunity for the redevelopment to become a social catalyst by providing much-needed social and events space whilst delivering much wider benefits by using the landscape for climate change adaptation, improving flood resilience and reducing the impact on the receiving sewer and wider environment.
At the heart of the design is a range of multi-functional SuDS features, including planted basins, raingardens and rainsculptures. The majority of resurfacing was completed with permeable paving, which captures the rainfall and directs it immediately below the surface of the pavement to two planted basins.
Significant onsite constraints were present such as high-voltage power cables and concrete slabs that formed the substructure of the existing roadway.
McCloy Consulting, the project engineers, adopted an innovate approach for the permeable pavement design to reduce costs and minimise requirements to dig out existing concrete, with permeable pavement being formed directly onto the slab no more than 200mm deep. This enabled the main basins to be designed by Robert Bray Associates as shallow features that sit comfortably within the landscape.
The hydraulics of the flow controls designed by McCloy Consulting restrict flows to below one litre per second. This is a different approach to that which would normally be applied and it provides greater benefit to the receiving combined sewer, reducing combined sewer overflow spills and the risk of urban flooding, while significantly exceeding normal compliance requirements without any additional cost to the client.
Success and looking to the future
This innovative project was completed in September 2015 and showcases an exemplar of how SuDS can be successfully integrated as part of the landscape of our towns and cities. The scheme has received awards from the Institute of Civil Engineering and Sustainable Ireland.
McCloy Consulting (which has offices in Belfast and Dublin) is currently undertaking a two-year monitoring study to assess the impact of the scheme on peak and base flows to the combined sewer. The outputs from this study have the potential to inform future strategies for runoff management as part of citywide regeneration projects.
Anthony McCloy, managing director of McCloy Consulting (specialists in flood risk, SuDS, contaminated land and monitoring with offices in Belfast, Dublin and London). Email: firstname.lastname@example.org / email@example.com