Project reference: Tampere City Stormwater Program

The project was complemented by parallel studies created for urban planning: In the flood study, flood maps for lakes in the city center were created, along with a stormwater network model and flood maps for network areas. In the small water study, the streams and springs in the city center and Nurmi-Sorila area were classified based on their natural state in 2022, and ponds, lakes, and lake shore areas were classified in 2023. Additionally, a map was created to identify streams that should remain open and those that can be opened from pipe infrastructure.

The City of Tampere is committed to a significant improvement in water quality and water use efficiency as one of its objectives. The purpose of the Stormwater Program is to promote more natural management of stormwater, including the use of blue-green infrastructure. Blue-green infrastructure refers to the construction of green spaces and street vegetation to manage stormwater by infiltrating it into the soil, delaying flow, and directing it.

"As a result of the update work for the Stormwater Program, the City of Tampere has received a much more comprehensive stormwater program than before. The program’s separate studies and action plans support the implementation of the program’s principles and objectives," says Pekka Heinonen from the City of Tampere.

Challenges and Opportunities for Stormwater in Cities

In cities, impermeable surfaces such as asphalt, various hard surfaces, vehicles, and roofs prevent water from being absorbed into the soil. This disrupts the natural water cycle and can negatively impact, for example, the formation of groundwater. Preserving groundwater is particularly important for the quality of drinking water. Stormwater from hard surfaces typically ends up directly in stormwater sewers, which lead to water bodies. The combined sewer system in the city center (wastewater and stormwater together) will be discontinued.

It is important for nature that stormwater is absorbed into the soil, and that there are either natural or constructed areas where water can collect or where the flow is delayed. Diverse vegetation areas are excellent places for nature to self-purify stormwater. Plants absorb nutrients, and water flows cleaner onward.

Project Goals

The framework for the Stormwater Program included three key areas: biodiversity, climate change adaptation, and communication to residents. The goals were set as follows:

• Promoting natural water circulation in urban structures
• Ensuring and improving biodiversity
• Securing the quality and quantity of groundwater and surface waters
• Managing stormwater floods and ensuring flood routes
• Developing the multifunctionality of stormwater structures
• Separating stormwater from wastewater

New Analytical Tools in Finland

AFRY prepared a catchment area study, water body and flood study, and a small water study, including field surveys and classification of waters based on their natural state. The catchment area study was mainly conducted using geographic information system (GIS) analysis, utilizing methods such as the Stormtac analysis and Sponge City green street analysis, which are still relatively underutilized in Finland.

The Stormtac simulation assesses the type of stormwater produced based on land use. High-traffic roads and dense city areas generate lower-quality stormwater compared to, for example, single-family home areas. The simulation can estimate the stormwater quality for a specific area.

In the Sponge City analysis, the possibility of implementing green streets in dense urban structures was evaluated based on the number of impermeable surfaces, street widths, traffic volumes, stormwater discharge routes, and topography. The analysis aimed to identify where such streets might be feasible, considering current activities and traffic. The result was a map of streets that meet the criteria, are at least 16 meters wide, and have low traffic volumes, for further research. Further studies will assess whether these streets can be transformed into stormwater green streets, where vegetation areas are created in the street area to act as stormwater routes, water absorbers, and flow delay systems. This solution also helps to mitigate common urban issues such as the heat island effect, noise, vibration, and windiness.

Important Information for the Client from the Studies

The City of Tampere is a pioneer in stormwater management by Finnish standards. The stormwater program and catchment area studies now created will help the city achieve its climate, sustainability, and biodiversity goals. The project established general principles for managing stormwater across the entire Tampere area, with specific guidelines for the city center and Nurmi-Sorila, as well as separate guidelines for groundwater areas. A map was also created to guide the maintenance of open streams and the opening of streams from pipes.

"The City of Tampere gained significant benefits from the project, especially since the update of the Stormwater Program was accompanied by the simultaneous completion of other comprehensive studies related to the theme: the Stormwater and Water Body Flood Study and the Small Water and Water Body Study in 2022 and 2023. The work package was guided by a broad group of city experts who met monthly with the consultant for project meetings. The work process was educational, and a significant amount of knowledge and understanding about the natural management of stormwater and its multi-benefit aspects for the city was gained during the process. The comprehensive study package ensured the quality of the stormwater program content and served as essential material for the concurrently developed city center phase urban plan 2021–2025," says Taru Heikkinen.

Project information:

• Client: City of Tampere
• Project: Stormwater Program and Catchment Area Study 2023–2030
• Duration: May 2022 – October 2023
• AFRY’s role: Consulting, Stormwater, Nature, and Landscape Matters

Pekka Heinonen, Green Areas and Stormwater, City of Tampere

Taru Heikkinen, Urban Planning, City of Tampere