Mitigation of the environmental impacts of the harbour tunnel
Lapinlahti Park’s natural and scenic values are taken into account in the planning of the harbour tunnel.
The Port of Helsinki and the City of Helsinki have chosen the route option for the further planning of the harbour tunnel that starts from the West Harbour, emerges at the southern edge of Lapinlahti Park and connects from there to Länsiväylä. The tunnel’s routing along the edge of Lapinlahti Park has sparked some discussion. The mitigation of environmental impacts is important in these types of large-scale construction projects, and the implementation of the chosen route requires mitigation of its impacts on local nature. To this end, the tunnel planning process has involved finding effective solutions for safeguarding the flora and fauna of Lapinlahti.
According to the environmental impact assessment of the project, the most significant issues to be addressed in the further planning of the chosen tunnel route concern the natural, scenic and culturo-historical values of Lapinlahti Park. The adverse environmental impacts particularly affect
- the Siberian flying squirrel,
- the turnip-rooted chervil and the depressaria chaerophylli moth.
In the continued planning, the Port of Helsinki has paid particular attention to preserving the living conditions of these species in the area, as well as preventing and mitigating other harmful environmental impacts.
During spring and summer 2024, the Port has explored the use of a thin rock roof construction technique in the tunnel. The solution will enable the entrance to the tunnel at the southern edge of Lapinlahti Park to be implemented with a significantly shorter open pit. The solution makes it possible to:
- preserve the trees and vegetation in the core area of the Siberian flying squirrel
- preserve more turnip-rooted chervil areas.
The Port of Helsinki has found effective solutions to safeguard the flora and fauna of Lapinlahti.
Living conditions of the Siberian flying squirrel to be secured
The Siberian flying squirrel is a protected species under Annex IV (a) of the EU Habitats Directive and Section 78 of the Finnish Nature Conservation Act, and the destruction or deterioration of its breeding and resting sites is prohibited. The Siberian flying squirrel has been monitored in Lapinlahti Park for several years, with three identified core areas for the species in the area, one of which is partly located along the planned route of the tunnel. This area can be preserved using the thin rock roof construction technique, which will allow the open pit of the tunnel entrance to be significantly shortened. In addition, the Siberian flying squirrel’s habitat can be protected through the following means:
- by scheduling construction activities causing noise and vibration to take place outside of the Siberian flying squirrel’s nesting season
- by preserving trees, specified as the implementation planning progresses, and planting protective trees
- by setting up nesting boxes for Siberian flying squirrels.
To guide the planning, the Port of Helsinki has requested an opinion from the ELY Centre on how effectively the planned measures mitigate the environmental impacts of the project. According to the ELY Centre’s assessment, the habitat of the Siberian flying squirrel will not deteriorate if the thin rock roof technique is used in its core area and noisy work is carried out outside of the Siberian flying squirrel’s nesting season.
The trees in the Siberian flying squirrel’s core area in Lapinlahti will be preserved.
Living conditions of the depressaria chaerophylli moth to be preserved
In accordance with Section 77 of the Nature Conservation Act, depressaria chaerophylli is a species subject to special conservation measures that is highly endangered in Finland. It is a moth species with a wingspan of about two centimetres, brownish-mottled in colour, and its larvae feed on turnip-rooted chervil.
The Port of Helsinki will secure the living conditions of depressaria chaerophylli in Lapinlahti Park by significantly increasing the numbers of its host plant, the turnip-rooted chervil, elsewhere in the park through sowing and supplementary plantings. The work began in spring 2024 with the preparation of a multi-annual turnip-rooted chervil planting plan. The aim is to ensure that there are enough turnip-rooted chervil growth areas in the park to prevent the deterioration of depressaria chaerophylli’s habitat.
The Port has requested a statement on the turnip-rooted chervil planting plan from the ELY Centre, which considered the plan viable. The ELY Centre emphasised the need to ensure an adequate compensation factor when compensating for the habitat of a highly threatened species. Because of this, the Port will be utilising the voluntary compensation tools provided for in the revised Nature Conservation Act in the planning of the project. The aim is to ensure that authorities and other stakeholders are able to assess the key environmental impacts of the tunnel project in a genuinely transparent manner.
The Port will prepare the aforementioned plan in collaboration with the City of Helsinki and engage in close cooperation with the ELY Centre as well.
The preparations based on the turnip-rooted chervil planting plan will begin in autumn 2024 with the preparation and sowing of turnip-rooted chervil seeds at test sites. The effectiveness of the plan, the growth of the turnip-rooted chervils and the presence of depressaria chaerophylli larvae will be monitored annually. The results of the monitoring will be utilised in the planning and to revise the turnip-rooted chervil planting plan, if necessary.
In summer 2024, a survey was carried out in Lapinlahti Park to determine the extent of the local turnip-rooted chervil growth areas and count the numbers of depressaria chaerophylli larvae and their feeding traces. The survey revealed that the distribution areas of the depressaria chaerophylli larvae were roughly the same as in the previous 2020 survey. However, the number of larvae was higher than in 2020. Based on the survey, the local depressaria chaerophylli population is currently doing well and has grown since 2020.
The use of the thin rock roof construction technique in the tunnel is also crucial for the living conditions of depressaria chaerophylli. It will allow the rocky tunnel section of the harbour tunnel to be extended, while reducing the length of the open pit section. Therefore, the method will also preserve the existing turnip-rooted chervils better than the original plan.
A plan has been drawn up to increase the numbers of turnip-rooted chervils, ensuring suitable habitats for the depressaria chaerophylli moths.