Tikkurila Dam, Vantaa, Finland

Introduction

The removal of the Tikkurila Dam in Finland is an exemplary model of a planning process which, with the full involvement of stakeholders, produced an outcome that is beneficial not only for river connectivity and migratory fishes but also for people.

The Tikkurila Dam was situated on the 65kms-long Keravanjoki (the Kerava River) which is a tributary of the Vantaanjoki (Vantaa River) which flows into the Gulf of Finland at Helsinki. The Vantaanjoki is the main watercourse of the 1685 km² watershed.

Tikkurila is a district and major region of the municipality of Vantaa which is located in the eastern half of the Helsinki conurbation around 16kms (10 miles) north of the centre of the city. Tikkurila is the administrative and commercial hub of Vantaa.

The dam was around 47m long, 3m wide and 4.5m high and was built from a concrete core clad with stone.

The concrete and stone structure of the dam.

HISTORY

A dam and mill operations had been in place at this site since the Middle Ages. The most recent dam was built between 1912-1913. It used to generate power for the adjacent linseed oil factory but its original function ceased decades ago.

For many people living in the city, the Tikkurila Dam had cultural importance. The old linseed oil factory is a listed building and the dam was considered by many to be a vital part of its history and the surrounding area. The dam was never listed but it was a valued part of the city’s landscape and in the past the city museum had stated on many occasions that the dam should be preserved. Vernissa, an arts centre for the city, is located in the old factory building and is a focus for many cultural activities.

View looking along the dam towards the old linseed oil factory buildings.

However, although it had been restored in 1994 and a fish ladder installed, the dam still formed an obstacle for migratory fishes. With an increase in fish numbers in the river below the dam, there was the potential to create not only an optimal habitat for trout above the dam but also a significant fishing destination for anglers.

The redundant fish ladder.

PLANNING THE REMOVAL AND COST

The planning and decision-making process was a long and thorough one. There were several committees which had their own, distinct responsibilities.

The project team was made up of the following groups:

1. The Steering Group formed of staff members and experts from Vantaa City authority departments and service centres, including landscape architecture, city planning, bridge engineering, water supply, sports (fishing), land use and environmental planning, and representatives from Vantaa City Museum and other stakeholders.

This group gathered information and steered the planning process.

2. The Design Group headed by staff from Ramboll Oy, a leading engineering consultancy company, with experts in landscape architecture, geotechnical engineering, structural engineering, water resources engineering, municipal engineering, hydrobiology, contaminated soils, lighting, cost accounting, and the fishing industry, and sub-consultants in fishway structures and underwater soundings.

This group carried out many of the required surveys.

Project meetings were arranged about every six weeks, where topical project issues would be discussed among the Steering Group and the Ramboll Design Group. The Steering Group was in charge of giving adequate source information to the Design Group and handling all administrative issues, such as applying for a water permit.

Hanna Keskinen, Project Leader, Chair of the Steering Group and Head of Park Planning for the city of Vantaa at the time of the project, was responsible for presenting the results of a pre-survey and the final general plan to  

3. The Technical Board which was composed of experts from the city of Vantaa and other stakeholders chosen by the City Council. This committee was responsible for ‘directing and monitoring production of services in the City’ and ‘enhancing the residents’ perspective when developing service production’. It made the final decisions on design issues.

After receiving reports on the pre-survey and final plan, the Technical Board gave the green light to procede with the project.

The client for the project was the Public Utility Services Centre of Vantaa.

The decision-making process not only had to solve the technical problems to allow the dam to be removed: it also sought to implement the principles of Blue-Green Infrastructure.

Blue-Green Infrastructure is understood to be all natural and semi-natural landscape elements that form, or could form, a blue-green network. It can refer to landscape elements on various spatial scale levels from individual rows of trees to complete valley systems. Green landscape elements can be hedgerows, copses, bushes, orchards, woodlands and natural grasslands. Blue landscape elements are linked to water and can be pools, ponds and pond systems, streams, rivers and other water courses. Together they form the blue-green infrastructure.

In the context of an urbanised environment such as Tikkurila, and if the dam removal was to conform to these principles, the project had to aim for the recreation of a naturally-oriented water cycle while contributing to the amenity of the city by bringing water management and green infrastructure together. In this way, a multitude of environmental, ecological, socio-cultural and economic benefits could be generated.

The decision-makers in Tikkurila also had to take account of national and international strategic plans and policies. As part of the European Union (EU), Finland is bound by the Green Infrastructure Strategy which the EU adopted in 2013 ‘to promote the deployment of green infrastructure in urban and rural areas’. This is a key step in implementing the EU 2020 Biodiversity Strategy and specifically Target 2 that requires that ‘by 2020, ecosystems and their services are maintained and enhanced by establishing green infrastructure and restoring at least 15% of degraded ecosystems’. Restoration action is also seen as a crucial response to climate change.

To comply with the EU’s relevant policy framework, the Finnish Biodiversity Strategy and Action Plan for 2020 provides the basis for the Green Infrastructure (GI) policy in Finland stating that “ … detrimental impacts on biodiversity due to the fragmentation of natural areas must be prevented or reduced, by developing so-called green and blue infrastructure.” The Green Infrastructure policy is also seen as a key part of the sustainable development of urban areas.

Vantaa’s blue-green landscape elements – water and riverside vegetation.

January 2015 – Planning begins with The Pre-survey

It became clear, with every dam inspection, that the dam was deteriorating and in need of restoration. The city authorities of Vantaa decided to carry out a pre-survey project and this found that there were pressing reasons why the situation needed to be resolved. These were:

• The deteriorating condition of the dam.
• The technical fish ladder was not working properly because the opening was located too far from the dam. Radio transmitter research showed that fishes were spawning in the Tikkurilankoski (Tikkurila rapids) below the dam but although there had been a recent increase in trout numbers in the rapids, the number of spawning trout was still small.
• Pressure to develop more recreational areas near the city centre of Vantaa due to the projected increase in population.

Tikkurila rapids below the dam with the old linseed oil factory on the left.

Hanna Keskinen, Project Leader, commented on the decision to start the pre-survey:

“Refurbishment of the dam was inevitable due to the repair requirements that were presented at dam safety inspections. There was a strong desire to investigate if the dam could be removed, from both the technical directors and politicians. Still, removal of the dam was decided on only after the pre-survey had been done and approved by the technical board.” (Keskinen 2017, translated from the Finnish)

The pre-survey was launched in January 2015 with four main objectives:

1. find practical solutions for the future of the dam
2. create a functional fish passage
3. assess the impacts of 1 and 2 above and
4. make an estimate of the cost of construction works.

To inform these objectives, the pre-survey had to gather data about flood management, environmental disturbance, soil composition, recreational use, cultural history, fish and benthos, cityscape, the value of the natural world, the soundscape and former use of the area.

Information came from a variety of sources such as the city’s development goals for the riverfront and its adjacent land, old photos of the area, the perceptions of users and maintenance personnel, and contributions from the City Museum and other members of the diverse Steering Group.

To give everybody the opportunity to be heard, an egalitarian approach was adopted which in turn maintained good communication between members of the Group.

Raising awareness

In 2015 and 2016, the city of Vantaa carried out awareness-raising projects by establishing a theme for these two years focusing on brooks and rivers. The main goals were to engage residents and organisations in care-taking and restoration activities connected with developing diversity in flowing-water landscapes and improving the resilience and recreational use of brooks and rivers.

Public opinions

Planning also took account of the opinions of users and stakeholders, both for and against. A bulletin of the goals and the planning process was released which received 37 comments from residents of Vantaa, active fishermen, companies and environmental organisations. Most of the feedback was encouraging and in favour of the removal of the dam on the grounds of a more ecologically-sound and fish-friendly river environment and better recreational possibilities.

Comments displayed the pride that local people had in their city and their engagement with the city’s environmental issues: they praised Vantaa for showing an example to others by removing an old dam and restoring the natural state of the river; they mentioned that Vantaa could be part of a trend taking place in other countries to remove obsolete barriers and improve conditions for migratory fishes; and that removing the dam would bring a lot of positive publicity to the city and enhance its image of a sustainable and bio-diverse place to live.

“By removing the dam, you’ll create a gorgeous place to enjoy a free-running river in the middle of the growing Tikkurila, and at the same time you’ll enable easy passage to upstream spawning grounds for migratory fish, for example trout.”

“Vantaa would be a forerunner in the growing positive trend of removing disadvantageous water structures that impair biodiversity.”

“I and hundreds of other volunteers could be aiding in river restoration to increase fish spawning!!!”

“I think that the dam of Tikkurila should definitely be removed and restored as a diverse whitewater area, that would serve city dwellers as well as fishermen in the future.”

“Vantaa as a brave forerunner towards a more sustainable and greener nature.”

Fishermen made useful and positive suggestions about how conditions in the river could be enhanced for fish species: that there were natural rapids with bedrock that could be repaired with little effort to provide a habitat for trout; that there were many small brooks upstream where trout could spawn if river connectivity was restored; that the Tikkurilankoski (adjacent rapids) could develop into a popular and profitable place for fishing.

Other comments noted that the removal of the dam would enable an unhindered passage through the centre for canoeists and kayakers and that leaving the dam in place would be more expensive in maintenance costs than restoring the natural rapids.

There were also some people who raised technical concerns and expressed opinions that were unfavourable towards the dam’s removal:

“I object to the partial removal of the dam, because it is a part of the great industrial and village history of Tikkurila.”

In April 2015, the local newspaper ‘Vantaan Sanomat’ (Vantaa Despatches) asked their readers whether the dam should be opened up or not. Out of 953 responses, 96% were overwhelmingly in favour of the dam being removed and 4% were against. In April 2017, another poll was taken after a resident’s letter was published in the newspaper and 91% strongly agreed with the dam’s removal while only 9% wanted to preserve it.

During the pre-survey it thus became evident that three aspects with special importance needed to be considered and accommodated in the new plan for the area: ecology (especially fish), recreation and cultural history. There was a strong desire to integrate these three aspects into the final plan, not only to enable easy fish passage but also to build an attractive waterfront which still maintained a visible reminder of the dam as a part of the early 1900s factory surroundings.

Four options for action

Four plans were evaluated by the Steering Group in light of fisheries and fish production, other benthos, water landscape, recreational use of the waterfront, cultural history, fishing, construction costs, costs for upkeep and effects on water level.

The options presented were:

0+  Refurbishment of the fish ladder (minimum work and cost)

1    Partial removal of the dam

2    Complete/nearly complete removal of the riverbed section of the dam

3    Complete/nearly complete removal of the riverbed section of the dam and the fish ladder and the creation of long natural rapids with spawning beds, fish nursery areas and protective rocks to achieve the maximum fish reproduction and habitat area. The greater part of the banks and riverside vegetation would remain unchanged and water flow speed would remain moderate. Low water levels in the summer would be compensated for by building an underflow channel to provide enough depth of water for fishes to swim through.

Option 3 involved the maximum amount of work and cost.

August 2015 – Decision by the Technical Board

After discussion, the Steering Group chose Option 3. This was presented to the Technical Board, which agreed to the following:

• the dam would be preserved and refurbished on both sides for a length of 5-15 metres
• the centre part would be dismantled to enable unhindered passage for fish and benthos
• the old groundsills would be refurbished if needed
• the banks would be supported by landfills to allow more space for recreation
• a new path and recreation area would be constructed on the north bank
• the waterside slope would be shaped and planted as a meadow.

These decisions were then subjected to computer modelling and visualizations leading eventually to the final General Plan.

Only the central portion of the dam was to be removed.

Landscape architecture competition

An important element in the planning process was the decision by the city authorities to hold a competition for the redevelopment of the river frontage around the dam site. As well as the linseed oil factory, there were other historic buildings in the vicinity which had to be taken into consideration such as the old silk factory and Heureka (the Finnish Science Centre). The competition, launched in 2015, was held to increase appreciation of the area and obtain a variety of suggestions for future improvement.

Responses to a questionnaire to elicit people’s feelings about the waterfront produced some contradictory results but generally they highlighted the area as an important recreational asset with diverse natural resources which could be developed as a pleasant and multi-functional space for residents.

The winner of the competition was Loci Maisema-arkkitehdit Oy.

February 2016 – General planning starts

The general planning phase involved the conducting of numerous surveys. These included the mapping of the underwater in-channel structure, an analysis of contaminated soils in the area, a survey of the structural condition of the old kiln smokestack, an ocular survey of the structural condition of the dam and fish ladder, and a survey for thick-shelled river mussels. Re-use of the concrete and stones of the old dam in the new construction was also considered.

Soil analysis revealed that the soil on the north shore was highly contaminated. The most problematic soils were in the immediate environment of the old kiln smokestack. It was estimated that the total volume of contaminated soils in the redesigned area would be up to 1200m³ which needed to be excavated and removed or covered with a layer of new soil.

More work was also carried out on compiling the application for a water permit, modelling the channel hydraulics, and designing the physical removal of the dam, fish ladder re-use, the channel structure and the river banks on the upstream side of the dam.

Species surveys

A survey of the populations of thick-shelled river mussels, carried out by Ramboll, found the greatest number to be in a backwater in front of the Heureka science centre (estimated population size 2900) but more congregations were found above the dam pool (125 mussels), in the dam pool (800 mussels) and in the downstream rapids (46 mussels). It was decided to move the mussels in the dam pool to a suitable habitat, further away from the demolition site.

A surveyor records thick-shelled river mussels ready for translocation.

Electro-fishing, which is carried out every two years on the Keravanjoki to determine the species and biomass of fishes in the river, recorded a variety of species in 2015. Stone loach, miller’s thumb, burbot, bleak, roach, gudgeon and sea trout (both released and wild) were found. The biomass caught from the Tikkurila rapids survey site was in total approximately 1800g/100m². Although the amount of trout fry originating from natural spawning was exceptionally high and had been increasing in the Vantaanjoki downstream, the density of older fry in the rapids was low, in common with trout density generally in the Keravanjoki.

There was much discussion on the best way to provide for trout spawning habitats. The area of the dam pool had been a rapid before it was dammed and it could be seen on photographs taken in 1994 that the river bed included bedrock and rocks of various sizes. Some opinions supported a more natural approach to the dam removal and river restoration process. They suggested that, after the dam was removed, the rapids would take shape naturally and return to their original state and fishes would be able to migrate as they had done before the dam was built. Others suggested that the stream velocity was too fast for the fishes to ascend and the rapids would need groundsills to slow the speed and distribute water across the whole width of the river bed. The groundsills would also help to create more habitats since they provide varying water depths.

November 2016 – General Plan passed

The results of the surveys were presented to the Technical Board as part of the General Plan and this was accepted by the Board.

February 2017 – Water Permit application

The Steering Group had the responsibility of applying for the Water Permit. According to Finland’s water legislation, water permits are required for all activities affecting constructions in waters or the water supply. The application was made public as appropriate, giving the relevant authorities and anyone affected by the plans time to comment and make proposals concerning the requirements for the permit.

April 2017 – Detailed planning starts

Detailed site planning started only after the General Plan had been passed by the Technical Board and a water permit application had been made.

Planning work included details of how the the central part of the dam was to be demolished and preliminary instructions for the organisation of the construction site. It covered the geotechnical and municipal engineering required on the banks for erosion control, river restoration design, including the new channel bed in the reach of the river most affected by the removal, and vegetation design in the sub-water channel area. It contained measures for excavating/covering the contaminated soils and the excavation and filling work that was required in the dam pool, and the design of a path for anglers on the south shore.

February 2018 – Water Permit granted

Spring 2019 – Detailed planning completed

Detailed planning for the removal was completed by Spring 2019. All was ready for the dam to be removed.

3rd June 2019 – Dam is removed

In June 2019, the hard work came to fruition when a central section of the dam was removed, allowing the Keravanjoki to flow unrestrained through Vantaa. Crowds gathered on the riverside to watch this important moment in the City’s history. There were speeches and music, and cheering as the dam was breached.

The Keravanjoki flows freely through the central part of the dam.

Crowds cheer as the Tikkurila dam is finally breached.