Case study:Restoration of Porvoonjoki

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Location: 60° 25' 16", 25° 36' 40"
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Project overview

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Status Complete
Project web site
Country Finland
Main contact forename Vainio
Main contact surname Sampo
Main contact user ID User:Kasvio
Contact organisation Itä-Uudenmaan ja porvoonjoen vesi- ja ilmansuojeluyhdistys
Contact organisation web site
Partner organisations
This is a parent project
encompassing the following
The River Porvoonjoki

Project summary

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The river Porvoonjoki is the main river of the catchment area of the Porvoonjoki. The river runs from Lahti region to the City of Porvoo. It passes by many agricultural fields that are highly culturally significant to the area. The river is 143 km long anf the catchment area is 1 271 km2. The catchment area has only 1,4 % of lakes. The delta of the Porvoonjoki river is a Natura2000 area. The current has been more than 200 m3/s. The river has several rapid areas and 18 rapids have been restored to help the fish to migrate upwards the river. May restoration were done in the triburatory of the main river. Also fish (roe boxes and juveniles) have been introduced to the rapid areas. The fish populations have not risen as hoped due to the fishing and the obstacles to migrate.

Most of restoration actions are done by the local volunteers. In most of the restoration cases the rapids have received gravel, stones and also the paths for migratory fish have been opened. The stones will modify the current in the streams and give shelter areas for the fish. The gravel gives the salmonid fish places to reproduce and lay eggs.

The river is naturally very humid because of the loamy bottom. Agriculture and the sewage water from the domestic areas affects to the nutrient load to the river significantly. Buffer strips along the river have been established to prevent the nutrient load to the river. Fish studies have proven that the sewage waters that contain wastes from medicine affects the reproduction of the salmonid fish. The water quality In the river is getting better because of the better seage water management systems and water conservations actions in the agricultural areas.

The river is very popular as a recreational area. Many turists come to Porvoo for recreational fishing and to canoe in the River Porvoonjoki. There are many fish species in the River Porvoonjoki: salmo trutta, salmo salar, grayling, perch, pike, char.

There are several small hydropower stations along the River Porvoonjoki and its streams. Also there has been many old saws and mills but many of them have been opened up and now the fish can migrate upwards.

Monitoring surveys and results

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Lessons learnt

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Thanks to the local volunteers the restorations have been very succesfull and now the salmonid fish and many other fish species have better conditions to live and reproduce in the river. Still there are many barriers to the migratory fish and those issues need to be taking into consideratin in the future.

Image gallery

The Koskela rapids before the restoration (photo:Vainio)
The Koskela rapids after the restoratrion (photo: Vainio)
The River Porvoonjoki in the City of Porvoo

Catchment and subcatchment


WFD water body codes
WFD (national) typology
WFD water body name
Pre-project morphology Straightened
Reference morphology
Desired post project morphology Actively meandering
Heavily modified water body Yes
National/international site designation
Local/regional site designations
Protected species present Yes
Invasive species present Yes
Species of interest Sea trout (Salmo trutta), Brown trout (Salmo trutta), arctic charr (Salvelinus alpinus)
Dominant hydrology Ephemeral
Dominant substrate Clay
River corridor land use Intensive agriculture (arable)
Average bankfull channel width category 5 - 10 m
Average bankfull channel width (m)
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Average bankfull channel depth (m)
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Mean annual discharge (m3/s)
Average channel gradient category
Average channel gradient
Average unit stream power (W/m2)

Project background

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Project started
Works started
Works completed
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Cost for project phases

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Investigation and design
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance

Reasons for river restoration

Mitigation of a pressure Hydropower
Hydromorphology Continuity for organisms, Width & depth variation
Biology Fish: Abundance, Fish: Species composition
Physico-chemical Nutrient concentrations
Other reasons for the project


Structural measures
Bank/bed modifications Barrier removal, Creation of gravel banks, Creation of fish passes
Floodplain / River corridor Barrier removal
Planform / Channel pattern Creation of meanders
Non-structural measures
Management interventions
Social measures (incl. engagement)


Hydromorphological quality elements

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Physico-chemical quality elements

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Supplementary Information

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