Last September, during the iWater 4th international event, the city of Turku had the opportunity of showing built-out stormwater management solutions in four different sites.
The visit around Turku’s built stormwater solutions started at Haarla wetland in Hirvensalo. Haarla detailed plan was approved in 2002, and the storm water solution was initially built as a pond in 2004. After several complaints from residents who saw the pond unsafe for their children, the dam that kept a permanent volume of water in the pond was removed, and the pond turned into a wetland.
We also visited the Syvälahti swale in Hirvensalo which was built in 2015. The swale, next to the Syvälahti School, has a double function. Besides its stormwater drainage use, it works also as an overflow area for both stormwater and seawater floods.
Skanssi is one of the newest and biggest development areas in the City of Turku. The site includes an ambitious open stormwater system sized to capture a peak discharge of a 100-year storm. The site development has been divided into several distinct phases. The first one, including the construction of part of the main street, Skanssinkatu, was completed earlier this year, in 2017.
The drainage solution in Skanssinkatu is a combination of infiltration trenches and pipes; there are no inlets or manholes in the street. The infiltration trenches situated along the street capture the surface runoff. Perforated pipes at the bottom of the infiltration trenches and overflow inlets in the swales collect the stormwater and discharge it into the city’s drainage system. The Natural Resources Institute Finland and the City of Turku are conducting a study in Skanssinkatu to test the use of different water resistant plants as part of stormwater solutions.
Finally, we visited Jaaninoja in Biolaakso. Between 2000 and 2003 the City of Turku restored a green ditch situated in a commercial area to give it a more natural, stream-like appearance. The stream restoration, which is part of the EU funded project Elävä Jaaninoja, aimed also at the creation of a park around the stream to improve water quality and biodiversity in the area. The result is a multifunctional open drainage system that brings several recreational and natural values to the site.