Recently I crawled through one of the world’s longest fish ladders constructed inside the rocks. Why? Because we want to find out if the fish ladder can be reopened for salmon.
I found myself along Reinforsen in the river Rana. The fish ladder is about 470 meters long, of which about 400 meters is inside the hillside. When it was built in 1957 it was the world’s longest fish ladder blasted in rock.
The main reason why some fish ladders are built wholly or partially through mountain is because of difficult terrain. It may be too steep, inaccessible for construction, or an open fish ladder is at risk to be destroyed by flooding and ice jams. This fish ladder was built to get salmon beyond the 29 meter high Reinforsen waterfall, so that salmon reproduce on the long stretch further upstream.
It is important to strengthen the salmon population in the river Rana. At the same time, it is also important to produce hydroelectric power.
SINTEF’s knowledge on the interaction between the environment and energy production can in this case be utilized to optimize hydropower operations in such a way that it does not affect fish migration negatively.
This fish ladder had not been maintained for a several years, but there is a desire to reuse it again as soon as the salmon parasite (Gyrodactylus salaris) is extirpated. The parasite was discovered in the river in 1975, and then the fish ladder was closed to prevent parasite spreading farther upriver.
My assignment was to make a review of the fish ladder. I should consider whether it could be used as it was, what repairs were necessary, or whether it was necessary to plan a completely new fish ladder on the opposite side of the river.
Conclusion of inspection; – yes, despite its age the fish ladder can be repaired, but it is also possible to build a new fish ladder on the other side of the falls. This is up to our client to decide. Anyway, we need a fish ladder adapted to this waterfall, to let the salmon migrate further upriver.
Find out more about CEDREN – Centre for Environmental Design of Renewable Energy.
About fish ladder:
A fish ladder requires a route where the slope is 1: 6 or flatter. Should we, for example, build pools and weirs past a 10 meter high waterfall, the ladder must be at least 60 meters long. It can often be a challenge to find good pathways. However, there is always bedrock where there a waterfall is located, and then there is an opportunity to blast a tunnel through the rocks. In many ways, you choose the route in the same fashion as when constructing a road or a railway. Sometimes it is wise to go through the mountains, such as the one in Reinforsen.