How to revive landscape and ecology of constructed rivers?

Ämmäkoski rapid in Varkaus in the new minimum flow situation. Photo: Jukka Jormola 

Rapids are one of the most impressive landscape types. Most big rapids in Finland were sacrificed for powerplant construction from the beginning of the 20th century and especially after the second world war, as electricity was needed. Still today power industry stresses the importance of hydro power for regulation of the electric grid, even if also other methods for balancing energy are developing. Environment policy requires measures for continuity of rivers and restoration of biodiversity. 

Renewal of powerplant permits in some rivers has begun in Finland but the legal processes seem to be lengthy.  In the evaluation of new requirements, good examples with scientific evidence are essential, to show benefits for fish stocks and for improvement of landscape qualities, compared to losses for energy production. In my research I have investigated three cases with habitat design and rapid restoration and reflected how to apply the results in four big rivers. In the cases I have worked both as a designer and researcher. 

Imatra city brook was constructed in 2014 to be a new reproduction channel for the trout of river Vuoksi, where almost all natural spawning sites had vanished. From the first years onwards trouts adopted the brook, despite its limited discharge. The densities of juveniles have exceeded the average of natural rivers in Central Finland. The brook became also an additional touristic attraction near to Imatrankoski rapid. The brook serves now as an example of new compensating habitat for other power plants, to be applied in planning of migration routes. The power company Fortum accepted the idea for a bigger bypass channel to the next powerplant upstream. In the permit renewal of the two powerplants of Vuoksi an environmental flow, in this case a continuous small discharge, is proposed to the Imatrankoski rapid. 

In the city of Varkaus into the Ämmäkoski rapid, connecting the Saimaa lake system, a minimum flow of 10 % of the average discharge has been lead since 2021. A bypass channel was constructed around the regulation dam. The city got its rapid landscape back. According to a video monitoring the bypass channel serves now as a migration route between lakes also for weak swimming fish species and as a spawning site for trouts. 

In the city of Oulu the Merikoski rapid has been designed with pools and fountains, replacing the vanished rapid. The plan was made by architect Alvar Aalto as a replacement for the lost rapid which he admired. As an initiative of residents and supported by the city council, a proposal was made to restore the rapid by an environmental flow, referring to the amount of water movement required in the permit or released voluntarily to maintain the health of water bodies. This would bring back the rapid as an attraction of Oulu city and it would enable salmon to spawn in the middle of the city again. 

The first examples of reproduction channels and restored rapids, planned and examined in connection to this research, have already proved to be promising in reviving river landscape and fish stocks. Vanished rapids can be brought back as landscape elements by environmental flow.  They can also serve as reproduction sites for fish but measures to prevent impacts of big flood discharges to habitats must still be developed. In cases where small powerplants have been decommissioned and rapids have been restored, like in river Hiitolanjoki, results in juvenile production for lake salmon have been excellent. In rivers with several powerplants experiments are needed to see how fish stocks can develop. In my doctoral thesis I want to promote restoration of rivers and local activism with science-based evidence.

Author: Jukka Jormola. Aalto University, Landscape Architecture.

Key words: reproduction channel, compensative habitat, environmental flow

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