Sweco’s experts in land use, water supply and infrastructure design have now been the trusted partners of the Town of Pudasjärvi for over 10 years. The most important joint projects have been the Iijoki local master shore plan and long-term flood and stormwater planning. A riverside poses an even greater design challenge than a seaside, since the floods are harder to predict.
Over a decade, Sweco’s experts have carried out several street infrastructure and water management projects in Pudasjärvi. The town centre lies low by the Iijoki river, meaning that nearly all projects have had to take flood and landslide risks into account.
“Our partnership with Pudasjärvi is not limited to one or two things. Instead, we produce solutions to broader issues together with the Town’s professionals,” says Sweco’s land use specialist Tapio Tuuttila. In many projects, local knowledge is as valuable as modern measurement instruments and design programs. “The people of the Town are exemplary co-operation partners. They provide us with information, trust and support in every project.”
Land Use Engineer Markku Mattinen from the Town of Pudasjärvi is also happy with Sweco’s know-how, which is utilised with a low threshold as needed. “We have a wide range of designers available to us, and a multifaceted co-operation has developed over the years. Overall, our projects are under control and the designers are familiar with our region. Together, we can get work underway quickly.”
A peak flood hits approximately once a century
Riverside tourism is important to Pudasjärvi, Finland’s log house capital. However, peak floods that occur approximately once a century must be taken into consideration in all shore construction. One of the greatest challenges in land use is the fact that human memory is not enough for assessing floods.
“Many landowners do not remember the river having ever flooded dangerously high, so the desire to build on the shore is great,” Tuuttila comments. “However, in flood planning, all building parts susceptible to moisture must be one metre higher than the predicted flood peak.”
The overall water management situation and great fluctuations in different seasons must also be taken into account. More than half of Pudasjärvi’s land area consists of swampland, so water retention is at a low level. When snow melts rapidly in the spring, the situation is similar to a torrential rain in a city centre.
“Between a dry summer and a spring following a snowy winter, the water level of the river may fluctuate more than three metres,” says Sweco’s water management specialist Tuomo Ylimaunu. Another contributing factor is extreme weather phenomena caused by climate change, such as long drought periods and earlier springs. “If an ice dam forms on the river while the snow is rapidly melting as the temperature increases drastically, the flood may be as high as eight metres.”
Master shore plan to guide safe construction
The biggest project in the Pudasjärvi flood planning was the Iijoki local master shore plan ten years ago. The plan covers 100 kilometres of shoreline on either side of the river and over 8,000 hectares of land.
“Pudasjärvi did not have an existing master shore plan, so the planning process took around five years, including extensive nature, landscape and archaeological surveys,” Tuuttila says. Landowners were also heard extensively. “The result facilitates happy life by Iijoki without flood damage.”
“The master shore plan and the flood hazard map clarify land use planning and justifying planning solutions,” Mattinen adds. “No one wants to build in a flood risk area.”
Stormwater management behind floodbanks
Damming the river shores is not a suitable solution for broad areas, as building embankments changes the behaviour of floods. However, in protecting the Pudasjärvi urban area, dams are the only viable method.
“The floodbanks were built 20 years ago, and as legislation became stricter, we created damage risk assessments concerning the dams, as well as dam safety documents,” Ylimaunu says. The documents define aspects such as dam maintenance. “We calculated how floods can be kept within the watercourse and stormwaters behind the embankments. We must prevent the occurrence of internal floods in the urban area due to battling an external threat!”
Planning water management in a flood risk area requires a broad overall vision and continuity. “We have charted the stormwater networks on the terrain over several summers and, at the moment, we are renovating stormwater pump stations,” Ylimaunu says. “Together, we are making sure that the dams, the stormwater network and the pump stations are operational when they are needed.”