Lieto Municipality, Finland

Site area: 120m2
Watershed area: 24 ha

Spatial planning context:

The pilot site is located in a developing industrial area called Avanti. The area has transformed in the last decade to meet the requirements of the logistics sector and other businesses. Nowadays Avanti has high-traffic volumes.

Site-specific stormwater challenge:

Watershed area of the pilot site consists mostly of impervious surfaces such as paved streets and rooftops of industrial halls. Stormwater runoff is drained via stormwater pipeline network, causing high flow rates and velocities, thus creating a risk for the drainage system functionality and capacity. Due to the land use characteristics, contaminants like heavy metals, hydrocarbons and nutrients are often found from the runoff.

Site-specific stormwater solution:

The pilot area is located by the small ditch downstream of the stormwater pipeline outlet. A flow regulation well is installed into the stream to divert specific part of the flow to bioretention basin. Filter media and plants are used for the treatment processes. Inlet and outlet of the pilot structure are equipped with online flow and water quality monitoring systems.


Online monitoring at Lieto Avanti showed extremely rapid changes in stormwater flow and water quality. In addition, the functioning of the bioretention basin is seen in the reduction of water turbidity at the outlet.

Location of the solution prior to construction.

Bioretention pond under construction in May 2022. Overflow pipes and the grey colored transition layer covering the drainage layer are seen at the rear part of the bioretention pond. Brown filtering medium and erosion protection at the inlet are seen in the front section of the picture.

Bioretention basin after the construction in 17th of May 2022.

Bioretention basin after the rain event in August 2022.