Storm washes the streets of Turku. Water flows along with the asphalt towards a storm drain, under which a stormwater sewer network is waiting. The stormwater sewer conducts the ever-increasing stormwater flow towards the pipe outlet, from where the water plunges straight into urban brook Kuninkoja and eventually travels to the Baltic Sea.
With stormwater, unwanted compounds such as suspended solids, heavy metals, oil, nutrients, road salt, and debris also travel to the waterways. The situation described above is by no means exceptional, as typically, stormwater ends up directly into the water bodies, without any treatment. As a result, stormwaters increase the amount of pollutants in our water bodies and in the nature around them, while causing economic costs.
In recent years, stormwater quality management has become a key objective in urban development and new stormwater management solutions are developed all the time. Ideally, stormwater should be managed on-source, by decentralized solutions. By filtering, infiltrating, and delaying stormwater, various benefits can be achieved, such as mitigation of extreme weather conditions (e.g., flood peaks and droughts), reduction of pollutants entering water bodies, and improved water quality.
In undeveloped areas, the biological processes in the soil and in vegetation are taking care of the treatment of rainwater. By utilizing these processes, it is possible to achieve multiple benefits e.g., supporting biodiversity, improving the living conditions of pollinators, and local leveling of temperatures through vegetation.
Water and Environmental Engineering Research Group of Turku University of Applied Sciences have designed two biofiltration basins for stormwater quality management in urban areas, as part of the CleanStormWater project. Biofiltration basins are designed to utilize soil and vegetation and support the area’s blue-green infrastructure and the biota around them. For example, one of the selection criteria for the plants in the biofilter structure was that the species are local and preferred by bees and butterflies.
In addition to technical solutions, the project aims to develop a guideline for stormwater management quality, including the entire life cycle of the management structures. Our pilot sites are located in Länsikeskus in Turku and Avanti in Lieto. The process is now in the tender phase, and construction is scheduled to take place at the end of this year.
When developing something new, it is expected that not everything will go as thought. There have been a lot of twists and turns in the process that requires further investigation. However, the challenges faced in the pilot phase are a positive and welcome thing in the big picture of the project. The aim is to develop a comprehensive approach to the whole lifecycle from design to maintenance when working on stormwater management structures. The challenges will help to create an overall picture of what the process can hold and provide a better starting point for the future of stormwater management structures using biofiltration.