Flood reducing water management structures to be built to Espoo's Niipperinoja stream and Vantaa's Varistonoja stream

The measures are part of a joint project by the ELY Centre of Espoo, Vantaa and Uusimaa that aims to improve the condition of Lake Pitkäjärvi, the condition of which is currently only passable.

Niipperinoja floods to be prevented with organic floodplain

In Espoo, the flooding of the Niipperinoja stream to nearby fields, residential areas and recreational and outdoor areas will be reduced with a new floodplain. The flooding problems of the stream have been clearly highlighted in the resident surveys and events carried out in connection with the project.

Flooding will be prevented by altering the natural floodplain of Niipperinoja, that is, by widening the riverbed from its top part so that during heavy rains, the surface of the stream has room to rise without the water spilling over to the nearby fields.

In addition to flood damage, the plain will also reduce nutrients leaking from fields to the stream when the floodwaters rise. This will improve the water quality of the stream and reduce the nutrient load of Lake Pitkäjärvi, as eutrophic nutrients will stay in the fields instead of spreading into the lake through floodwaters.

The floodplain will be made during August.

The section of the Niipperinoja stream to be altered presented on a map(external link, opens in a new window)

Varistonoja to be altered to prevent flooding and improve water quality

The action to be taken in Vantaa is the alteration of the Varistonoja stream. The alteration will reduce the stream’s flooding to Vihdintie and the adjacent Petikko business area. Another goal is to further reduce the flow of nutrients and pollutants into Lake Pitkäjärvi in order to improve the water quality of the lake and alleviate its eutrophication.

The alteration will focus on the section of the stream that runs through Petikonniitty, i.e. in the area between Vihdintie, Ring III and the Petikko business area. The stream will be widened at the top part with a floodplain so that during heavy rains more water can fit in the stream, and the water level can rise without flooding the nearby areas.

Near the bottom, the riverbed will be kept narrower, so that the stream can have sufficient flow even during periods of low rainfall and drought. Keeping the flow of the stream at a sufficient level even during drier seasons is important for the plants and other organisms dependent on the water in the stream.

In addition, a small check dam made of stone and tree trunks will be built at the bottom of the stream to slow down the flow of water, allowing some of the water pollutants to settle to the bottom. This will improve water quality. The check dam will be placed in the stream instead of the originally planned wetland.

The alteration work will be carried out in August–September.

The section of stream Varistonoja to be altered presented on a map(external link, opens in a new window)