European Green Capital 2021, Lahti in Finland, develops new ways to manage its stormwaters to adapt to climate change - Lahti

European Green Capital 2021, Lahti in Finland, develops new ways to manage its stormwaters to adapt to climate change

The changing climate will increase not only the amount of rainfall but the probability of extreme events such as heavy rains and extended periods of drought. This change is globally noteworthy when designing systems for stormwater management. The city of Lahti, the European Green Capital 2021, has developed new smart solutions for stormwater management.

A well-functioning stormwater management system enhances the aesthetic qualities of the built environment and reduces stormwater-induced surface water pollutant loading and flood risks. It also enhances the quality and quantity of local groundwater reservoirs.

– Such a system is composed of traditional stormwater conveyance systems such as pipes and canals as well as open, nature-based elements such as wetlands, infiltration fields and rain gardens. These are designed with the aim of infiltrating and detaining locally formed stormwater on-site as opposed to purely transporting it untreated into receiving water bodies, says Juhani Järveläinen, Storwater Engineer at the City of Lahti.

During the past few years, Lahti, located in southern Finland and the European Green Capital of 2021, has put considerable effort into identifying relevant stormwater flood risks. Lahti has also identified areas of special interest in stormwater planning which have, for example, limited conveyance capacity or delicate ecological conditions in receiving waters. This data has been comprehensively reviewed and compiled into Lahti’s latest master land use plan, to be used as a basis for more in-depth land use planning efforts in the future.

– A breakthrough was achieved in qualitative stormwater management in 2020, when stormwater previously bound for Lake Vesijärvi was redirected into a newly built stormwater purification system. The new nature-based system removes pollutants such as heavy metals and eutrophication-inducing phosphorous from stormwater, says Järveläinen.

The novel system, built in Hennala area as a part of the New Smart & Clean Stormwater Solutions project, is composed of a sedimentation pool, an infiltration field, a constructed wetland as well as a channel system connecting the three. The core of the system is the infiltration field, which has been separated into three sections, each equipped with separate drainage systems and different bioinfiltration media.

Based on pre-construction lab trials by the University of Helsinki, all infiltration materials are expected to achieve purification efficiencies exceeding 90% for all critical stormwater-bound pollutants. Extensive monitoring efforts will be used to quantify the system’s performance in the coming years.

Additionally, in the summer of 2021 new stormwater filters were installed in selected stormwater wells located in the centre of Lahti. As a part of the Stormwater quality & sewer well -based filtration -project, their effectiveness in removing pollutants from stormwater will be quantified along with other practical concerns related their potential wide-scale application.

Additional information:

Juhani Järveläinen
Stormwater engineer, City of Lahti
+358 50 559 4083