Climate-assured cities

“Our aim was to evaluate how we could keep trees in our urban areas and make them feel better. The solution provided us with the added bonus of a storm water initiative,” says Malin Engström, head of Växjö Municipality’s technical services department.

Urban densification leads to the replacement of natural ground surfaces with harder, less porous materials. This increases the risk for overflowing storm water systems, flooding and the death of urban trees. A number of cities have identified new working methods through the project Climate-assured System Solutions for Urban Surfaces.

Tree-lined avenue

Like many other cities, Växjö has its low-lying areas that are prone to flooding during heavy rain. When Växjö joined the climate project, the renovation of an avenue of 100-year-old linden trees on Västra Esplanaden in the city centre was already underway.

This tree-lined avenue is a pedestrian area and is also used for cycle parking and over the years the gravel surface has been compacted. This makes it difficult for surface water to penetrate down to the trees’ root systems and impairs soil gas exchange. It also means that heavy rainfall runs off along surrounding streets, overloading storm water drains.

Given the deterioration in the living environment for these trees, the municipality decided to investigate alternatives to replanting. This situation was also impacting on other areas of the city.

“As soon as we had heavy rain, we experienced flooding on a street running parallel to Västra Esplanaden on pretty much an annual basis. This area is located in a depression. The problem occurs when the storm water pipes can’t cope and overflow. We have been taking measures on and off since the 1990s. It has improved somewhat,” explains Malin Engström, head of Växjö Municipality’s technical services department.

The redesign of the area around the avenue was implemented in stages. Resurfacing was carried out and the surface layer of the central reservation was replaced with a more porous material.

Half of the roadway to the west of the avenue was excavated and resurfaced with a less traditional and more aerating layer.

New materials have been used

While carrying out this work, Växjö Municipality’s technical services department saw an opportunity to infiltrate large amounts of storm water into the road structure. The solution offered the opportunity to rebuild the pavements along the avenue as a combined area with space for storm water storage/infiltration, with the additional advantage of providing space for the root systems of the old lindens. These combined measures have succeeded in relieving the storm water system. By improving the living environment of the lindens, it is expected that they will be able to continue to grow along the avenue for at least another 30 to 40 years.

Malin Engström explains what strategic importance the climate project had.

“Green spaces are becoming fewer and fewer and we are struggling for space in the city. The project has given us the courage to begin testing new solutions that allow us to better utilise our green spaces and streets,” says Malin Engström. A subsequent initiative has seen the municipality install a tree pit drainage solution linked to the storm water drains, that is able to swallow large amounts of water while avoiding waterlogging that may damage trees. The project has contributed to this innovation.