Lessons learned from the five SuDS projects
All five SuDS retrofit projects supported by Drain London had challenges and opportunities - whether in design, planning, construction, community engagement or monitoring. Each SuDS project has now been successfully installed and does what it was designed to. This section covers the main lessons learned from the five projects.
SuDS design and procurement
Several of the five projects were delayed or needed extra resources to deal with both SuDS measure redesign and procurement issues.
When the council was the main partner and the problem was local authority procurement, some changes were made to help prevent future delays. For example, Haringey Council tendered outside its highways framework contract so that a contractor with the right skills could be hired. Hammersmith & Fulham Council is also working on a way for SuDS design teams to access its highways framework contract rates without releasing sensitive information.
An important lesson from the Bridget Joyce Square project was that earlier involvement of the contractor in the design process would help reduce the need for redesign. The Climate-Proofing Social Housing Landscapes project also found that being able to provide a more detailed design led to a more successful procurement process.
It can be challenging to get funding for green SuDS schemes from local organisations that are likely to benefit most from them. This may be because most people and organisations don’t know what SuDS are or the benefits they can offer. Because of this, many SuDS schemes remain funded by local government and their agencies.
Exceptions to this are a limited but growing number of developers who are incorporating green SuDS into their development schemes. This is mainly due to London Plan policy, which requires developers to follow a ‘sustainable drainage hierarchy’ that encourages the use of green SuDS.
We hope these case studies will help address part of this problem. In addition, an online map of existing SuDS schemes across London will accompany the London Sustainable Drainage Action Plan. The map will provide details and links to more information. The aim is to both publicise SuDS and help people and organisations realise that SuDS are viable and increasingly in use across London.
This is why the London Sustainable Drainage Action Plan focuses attention on retrofitting SuDS where other works are already planned.
Two of the projects experienced potential issues with construction. There is a risk that contractors with no previous experience of SuDS measure installation may be unable to install the measures correctly. This can reduce SuDS function and lead to costly future maintenance and/or repair.
For large and complex projects, contractors must have previous experience of SuDS installation (as with the Priory Road project). Alternatively, the design team must be on site to supervise construction (as with the Bridget Joyce Square project).
Green roofs generally need an expert to identify whether the building can cope with the extra structural loading of the roof. However, as the Lost Effra project showed, community green roof building is possible with a willing contractor. It can also encourage wider take-up of green roofs across the community.
Smaller schemes, such as depaves and downpipe disconnection into a swale or raingarden, may not need experts or specialist contractors. Instead, they can be done by local people (subject to planning permission, if necessary).
One of the strongest themes running through the five retrofit projects has been the importance of engaging local people from concept and design to installation and maintenance. This is not an ‘optional extra’ but a crucial part of any successful SuDS project. If done well, it can:
- result in better-designed and multi-functional SuDS measures
- raise awareness of climate change, potentially leading to behaviour change
- encourage community ownership and maintenance of SuDS measures
- encourage additional SuDS measures to be installed in the neighbourhood
Monitoring water quality and quantity can be challenging. It needs to be factored into SuDS design, and requires specialist equipment and expert analysis. In addition, the monitoring industry is not yet set up to undertake all the different types of monitoring required for SuDS schemes (flow, weather, moisture, pressure, etc.) Many companies specialise in just one type of monitoring. This can make SuDS monitoring expensive.
Because of this, comprehensive monitoring was only included in two projects - Bridget Joyce Square and the Climate-Proofing Social Housing Landscapes project. However the Dale Court rain gardens at Priory Road were designed so that monitoring equipment could be installed in future. Monitoring can provide invaluable data to support the use of SuDS across London.
As technology improves and gets cheaper, and as SuDS take-up increases, we anticipate more monitoring will be included as standard in new SuDS projects.
The experience of the five demonstrator projects suggests that maintenance of new SuDS measures doesn't need to be costly. For example:
- the Alma Road project shows that maintenance costs are balanced, if not outweighed, by the benefits of the SuDS measures
- the Bridget Joyce Square project demonstrates that the maintenance costs of SuDS measures can be reduced through careful design
- the Climate-Proofing Social Housing Landscapes project’s maintenance costs are similar to the costs before the project began
- the costs of maintaining the landscaping at the front of Dale Court at Priory Road actually decreased as a result of the SuDS installation
- the Lost Effra projects are being maintained by the local community