As the 10th anniversary of the government’s seminal “Making Space for Water” document, Jason Shingleton calls for greater creativity within surface drainage design.
We’re fast approaching a decade since the Department for the Environment, Food and Rural Affairs launched its Making Space for Water programme championing a holistic approach to managing flood risk and coastal erosion in England. As time passes and the importance of dealing with climate change grows, the need to make space for water remains very much a key priority for consultants and engineers.
Finding a cost effective, fit-for-purpose solution that is sensitive to the geology and hydrology of the site and compliant with all of the relevant pieces of legislation, whether it be the impending implementation of the Flood & Water Management Act 2010, the European Water Framework Directive, National Planning Policy Framework (NPPF), Building Regulations Approved Document H3 or Code for Sustainable Homes, can prove a challenge in even the most straightforward of projects.
Add a few common on-site hurdles - such as existing drainage levels, bedrock, a high water table or contaminated land - and suddenly the surface water drainage and treatment element of the project can become one the most problematic.
Human nature being what it is, we tend to look for the answers to these problems in tried and tested applications, leading to the installation of either a traditional buried drainage and attenuation system or, perhaps more recently, a surface mounted soft sustainable urban drainage (SuDS) system. While there is nothing wrong with this approach, using either system in isolation is not ideal. Traditional buried drainage systems are great for dealing with the volume of surface water and mitigating flooding, but no one can really say that they improve the biodiversity of the site. Landscaped drainage systems might look good and improve biodiversity, but the fact that they are predominantly surface mounted means they are space intensive and restricting.
Buried drainage systems are great for dealing with the volume of surface water, but no one can really say that they improve biodiversity.
All of this presents us with a real challenge, which we can only really solve by being more creative in the way in which we manufacture, design and install our surface water management systems. Innovative manufacturers can introduce new drainage solutions which work in harmony with soft SuDS to meet all of the typical SuDS tests of providing amenity and biodiversity while mitigating the effects of stormwater quantity and improving quality. But there must be a market for these new ideas. Consulting engineers need to be prepared to challenge traditional design approaches and in many ways set the innovation challenge, while contractors can facilitate innovation and make sure that the innovations remains grounded, buildable and obviously cost effective.
As an example, the obvious approach in projects with issues such as existing drainage levels, bedrock, a high water table or contaminated land is to try to reduce the depth of the drainage system, thereby reducing the need to dig and the volumes of earth removed, and potentially downsizing the pipe systems required. Installing ponds and swales can help achieve this, but where space is at a premium it could mean using porous or non-porous hard surfaces with a geocellular sub base contained in an oleophobic/hydrophilic geotextile. This increases the water storage capacity of the sub base by over 200% compared to traditional aggregate sub bases and also doubles up as a pollution control technique, providing integrated water treatment from source, removing silt and breaking down hydrocarbons as part of a wider water management and treatment solution. What’s more this kind of light weight, high strength technology can be installed with excavation depths as shallow as 500mm - proving digging deep isn’t always the answer.
- Jason Shingleton is Polypipe’s water management expert