Lessons Learnt from Construction of Nature-Based Stormwater Solutions: Case Pori, Finland

What to consider when starting a construction project for a nature-based stormwater solution? The City of Pori has recent first-hand experience of the issue, and the experts involved in the MUSTBE project are sharing their knowledge.

The first two pilot sites of the MUSTBE project were successfully constructed at the end of 2024. The wetland restoration work was completed in November 2024, and the stormwater tree solution was completed in December 2024. Both innovative solutions for stormwater management are nature-based, multi-benefit, cost-efficient, and represent principles of sustainable development. The main benefit of the stormwater tree solution is the reduction of flood risk while the wetland restoration solution neutralises the low pH of the surface water caused by acid sulphate soils.

When something new and innovative is created, there is no previous experience of similar processes available. One of the objectives of the MUSTBE project is to share information and best practices based on first-hand experience. This can help organisations such as municipalities in their plans to implement modern and sustainable stormwater treatment solutions.

The following best practices are proposed by the technical sector of the City of Pori, as the developer of the pilot sites and one of the partners of the MUSTBE project:

1. You should have a clear vision of the proposed nature-based solution: think about what you want out of the solution and what are the key goals that need to be achieved with it.
2. Be efficient, accurate, and quick in your construction planning and procurement. EU-funded projects often have a quite strict timetable. There may not be the same amount of time for design, construction and the research itself as in general in public sector work.
3. Good knowledge about nature-based solutions, building regulations, and quality requirements at all levels is more than beneficial. Even if you use a consultant you will need to understand how different nature-based methods work and be able to guide and audit your designs.
4. As the owner of the construction site, it is essential to take the time to supervise the construction work. During the work, you may often have to quickly react and come up with solutions, so stay on top of the progress at all times to make well-informed decisions.
5. Clear communication is needed on technical issues, so be prepared to explain why nature-based solutions are needed and how they work. When complex issues are communicated, it is essential to inform and engage stakeholders – you will probably never do it too much.
6. Working in an urban area often comes with limitations such as surrounding infrastructure. Take extra care in the design phase to make sure you’re accurately taking into account all the different constraints of the space for a successful integration of the solution. The nature-based solution should fit its environment, not fight with it.

Pori pilot solutions passed the “extreme weather conditions” test
In late November 2024, there were major snowmelt and heavy rain in Western Finland. This caused exceptional flooding in many coastal municipalities in Finland, which means that the performance of Pori’s nature-based solutions has already been tested in extreme weather conditions. The wetland pilot site’s water body got filled with water to its maximum limits. These kinds of harsh weather conditions were considered in the planning phase of the nature-based solution. The stormwater tree solution also proved its success during the exceptional flooding days. Neither flooding nor puddling occurred, which indicates efficient absorption performance of the new stormwater control structures. Summa summarum: both solutions worked as planned in managing the amount of stormwater.
The MUSTBE project is divided into three phases: a design phase, a construction phase and lastly, a phase for measuring the efficiency of the nature-based solutions. As such, the next step in Pori’s MUSTBE pilot sites is to monitor the water quality and amount. In the Pori central square, monitoring systems have been installed, and new ones will be installed to continuously measure the soil’s moisture levels, runoff levels and level of solids in the stormwater. In the wetland pilot site, the water quality monitoring will begin with real-time monitoring solutions including a weather station, groundwater level meter, flow meter, and pH meters.

For further information on the two pilot solutions is available here:

Pori’s Stormwater tree solution
Pori’s Wetland restoration solution