The City of Raisio protects nature in its stormwater and water management projects
The City of Raisio is developing its water services comprehensively. Stormwater management is already being considered in land use planning, and Sweco’s experts help to take into account the protection of the Archipelago Sea, the recreational use of local nature and the prevention of flood damage.
Runoff and stormwater management saves the Archipelago Sea
The cooperation between Sweco and Raision Vesi in municipal engineering and water supply projects has continued for ten years. Cooperation with the City of Raisio is carried out through a framework agreement. One of the current projects is the general plan for the runoff waters of Raisionlahti (2023–2027). Its goal is to reduce the amount of harmful substances and solids that end up in the Archipelago Sea.
“With Sweco’s encouragement, we are implementing a master plan for the entire catchment area at once, not just for the Järvenoja riverbed, which was our original idea,” says Susanna Väinölä, the city’s civil engineer. The implementation of the master plan has required extensive expertise in water management and aquatic nature. “Everything we have ordered has met our expectations.”
Anna Rouhiainen, Sweco’s Water Supply Asset Management Specialist, considers the development-friendly atmosphere to be one of the strengths of the City of Raisio and the water utility. “Raisio is ready to try new things, such as digital spatial data and modelling solutions.”
In his opinion, a great example of Raisio’s progressiveness is the hydraulic model made of the entire city’s stormwater network. Usually, only one part of the network is modeled. “Promoting stormwater management also requires experts like Susanna, for whom the topic is a matter of the heart.”
The importance of natural values for Raisio is also demonstrated by the restoration project of the Raisio River, in which Sweco assisted in guiding the construction of fishways from the perspective of aquatic nature. “The goal of water construction is always to create a natural footprint that the rapids area will not be recognizable as man-made in a few years’ time,” emphasises Janne Tolonen, Head of Sweco’s Aquatic Nature Team.
Multi-objective water supply planning
The City of Raisio is assisted by Sweco’s experts in asset management and aquatic nature. In this way, instead of fragmented information and separate reports, the city gets an overall picture that links land use, stormwater management and natural values.
“Stormwater projects are seen in Raisio in a great way as part of a larger whole, such as the protection of the Archipelago Sea, the preservation of biodiversity, preparedness for climate change and the prevention of flood damage,” says Tolonen.
Stormwater management aims to protect waterways, for example, through wetlands and other natural means. For the construction of the wetland, Sweco’s experts carried out nature surveys and inventories of streams and small water bodies in the Järvenniitty area. Moor frogs protected by the EU Habitats Directive were found in the area, which will be taken into account in the planning of the wetland.
“Nature surveys have been carried out immediately to the planning of the wetland, and our goal is not only to preserve the habitats of the moor frog, but to improve them,” says Tolonen. “For example, we are creating more shallow water areas that provide frogs with pleasant breeding sites.”
In Väinölä’s opinion, concrete measures immediately after the surveys are a clear indication to the city’s decision-makers and residents of what can be achieved with stormwater and nature surveys. “The planning of the wetland will also take into account the recreational use opportunities of the area.”
According to Tolonen, it is important to carry out aquatic nature projects in urban and urban areas where people live and move around. “When we bring nature-positive water protection solutions to people’s immediate environment, we also promote broader water protection goals, such as the protection of the Baltic Sea.”
The stormwater strategy provides guidelines for the stormwater programme
A growing city needs more residential areas, which also increases the need for stormwater management. In January 2025, Raisio’s stormwater strategy was completed, with background information such as a spatial data-based catchment area analysis.
“The analysis has also been utilised in Raisio Water’s leakage risk analysis, which aims to reduce the amount of leakage water in the wastewater network,” says Rouhiainen. The analysis includes an estimate of 50 wastewater wells located near depressions, ditches or streams that are prone to flooding.
A more goal-oriented stormwater programme is now being prepared, which will be prepared using workshops facilitated by Sweco. “Comprehensiveness is the most important thing in stormwater management, which is why a good end result requires the utilisation of the know-how of the city’s various experts,” Väinölä emphasises.
The cooperation between the city and the water utility is supported by the division of responsibilities table for stormwater management drawn up by Sweco. According to Rouhiainen, it clarifies the roles. “In maintenance, zoning and flood situations, it is important to know immediately how to act and who is responsible for what.”
In addition, Raisio is currently compiling a report that covers all of the city’s catchment areas to make it easy to utilise water supply and nature data in land use and zoning planning.