University of Oulu warns of flooding risks due to outdated stormwater systems in Finland

The stormwater systems built in earlier decades and ongoing urban infill construction may increase the risk of flooding in urban areas, warns Pekka Rossi, a junior assistant professor of water management at the University of Oulu. Rossi is involved in research examining how cities could enhance their stormwater management to mitigate flood risks, especially as rainfall is expected to increase due to climate change.

As part of the study, a digital model of the stormwater pipeline in the Lyöty area of Oulu has been developed to monitor how the network performs under various weather conditions. It was observed that the difference between old and new pipes, along with dense infill development, can exacerbate flooding risks. However, Rossi emphasizes that stormwater systems are not designed to handle every possible rainfall event.

“Our networks are typically engineered for rainfall events that occur on average once every 5 to 10 years,” Rossi explains. When rainfall exceeds this threshold, water overflows into designated flood routes. In places like Oulu, heavy rain often leads to street and tunnel flooding due to system overloads.

City planning plays a crucial role in managing stormwater. Developing green spaces that absorb water can aid in stormwater retention. Rossi notes, “Effective urban design significantly influences stormwater management.”

Additionally, the University of Oulu is researching methods to purify stormwater to reduce contaminants in local water bodies. Current trials in Oritkari involve using settling basins and bioreactors to cleanse stormwater. The research aims to better understand nutrient and metal concentrations before and after treatment, potentially providing solutions for future use in similar areas across Finland. The structures built for this project will remain in Oritkari after its completion in 2026.