Published on: 2.12.2019

Information produced by Finnish Environment Institute

Natural stormwater management

Natural stormwater management has many advantages: it reduces pollution in rivers and lakes, mitigates flood damage, enriches urban nature and even saves money.

Natural solutions are today sought for treating rainwater accumulating in the streets and on other impervious surfaces. Small volumes of water can be conveyed into swales commonly built on roadsides, where the water is infiltrated into the soil.

Stormwaters can also be filtered through soil layers. While a biofiltration area may look like an ordinary lawn, underneath it there is a system of subsurface drains that collects the water. Filtration removes at least nine tenths of heavy metals and phosphorus found in stormwaters.

Special wetlands are also built, which retain stormwaters for long enough to clarify and purify them before they are conveyed into a lake or river.

As part of cities’ green space networks, different stormwater solutions diversify urban nature and benefit many plant and animal species. Residents can enjoy an enriched spot of nature which offers enjoyment and promotes their health and well-being.

The city saves money as stormwaters are treated close to their source, rather than needing to be conveyed elsewhere. It has been calculated that a park one hectare in size at the very centre of a city saves the city more than EUR 200,000 a year.

Image: © Lasse Häkkinen, Lahden kaupunki