Flooding in Varistonoja in Vantaa and Niipperinoja in Espoo will be reduced by water management structures – event for residents explaining the measures on 1 February

Lake Pitkäjärvi covers areas in Espoo and Vantaa. The lake has become eutrophic, and streams feeding it have repeatedly flooded as a result of heavy rainfall. These problems have been tackled in a joint project of the ELY Centres for Vantaa, Espoo and Uusimaa, the aim of which is to improve the status of Lake Pitkäjärvi, which is currently in a below average state ecologically.

The project has extensively surveyed the problems of the lake and the catchment area and selected sites in Vantaa and Espoo where natural water management structures will be implemented to alleviate the situation. “Natural” means that no pipes or other unnatural structures will be built in the terrain. The measures to be taken include soil preparation, planting and possibly introducing natural stones to the site.

Varistonoja will be modified to prevent flooding and to improve water quality

The measures to be taken in Vantaa include modifying Varistonoja, which will reduce flooding on the Vihtitie road and the adjacent Petikko industrial park. Another aim is to further reduce the inflow of nutrients and impurities into Lake Pitkäjärvi via the ditch in order to improve the water quality of the lake and reduce eutrophication.

The ditch will be modified in the section flowing through Petikonniitty, i.e., the area delimited by Vihdintie, Ring III and Petikko industrial park. The ditch will be widened at the top to allow more water in the channel during heavy rainfall so that the water level may rise without flooding adjacent areas. The channel will be kept narrower close to the bottom so that there will be sufficient water flow at the bottom of the ditch whenever there is little rain and in dry periods. Water flow in the ditch in dry periods is important for plants and other organisms dependent on the ditch water.

Additionally, wetlands will be constructed in the ditch; in practice, these will be widened sections with planted wetland vegetation. Wetlands will slow down water flow, and the vegetation will bind contaminants and eutrophic nutrients, thus improving water quality.

 The section of Varistonoja to be modified on a map 

Flooding of Niipperinoja will be prevented with a natural flood plain

In Espoo, Niipperinoja will be modified to reduce flooding of the nearby fields, residential areas and the golf course. Resident surveys and events carried out in connection with the project have clearly highlighted the problems with flooding.

Flooding will be prevented by creating a natural flood plain in Niipperinoja, i.e., by widening the riverbed at the top so that the water level may rise without flooding the adjacent fields whenever there is heavy rainfall. In addition to other flood hazards, this will also reduce the leaching of nutrients into the brook from fields during floods. This will improve the water quality of the brook, as eutrophic nutrients stay in the fields where they belong.

 The section of Niipperinoja to be modified on a map 

Detailed implementation plans are currently being drawn up for both sites, and the modification of the sites will begin in the spring or summer. The modifications will be completed by the end of 2024.

Information event for residents on the measures and the project

The measures will be presented at a resident and stakeholder event on Thursday 1 February in the café in Espoo City Council Building at Espoonkatu 5. The event will take place between 17:00 and 18:30. It is open to all interested parties. You can also attend the event remotely via Teams. Link to the event.

The event will provide a general overview of the project and explain the measures to be taken in Varistonoja and Niipperinoja. There will also be time for discussion and questions. The event will be held in Finnish.

The project has produced plenty of information on the status of the Pitkäjärvi catchment area

The project has produced plenty of data on the status of the Pitkäjärvi catchment area and its issues. In addition to Varistonoja and Niipperinoja, some 20 other sites have been identified that would benefit from water management measures. The data will be used in the development of water management in the area in the future.

At the end of the project, an operating model will be drawn up for the planning of water management structures used in agriculture, forestry and built environment. This way, the data obtained in the project will benefit water management planning at a larger scale.

More information on the development of water management in the Pitkäjärvi catchment area project  (in Finnish)

The project is funded by the Ministry of the Environment’s water protection programme.