Rewilding Abramsån

Healing the silent wounds of a Norrbotten River

Rewilding Abramsån

Healing the silent wounds of a Norrbotten River

Background and project description

Abramsån, a tributary of the Råne River 45 kilometres south of the Arctic Circle, is a clear example of how severely many northern Swedish rivers were affected by the timber-floating era. To transport timber efficiently, the river was cleared of boulders and other natural structures. These interventions began even before the 1880s, and in Abramsån the impact went unusually far. On some stretches, wooden floors were even laid on the riverbed to make the waterway even more efficient for timber floating.

The result was a river that lost much of its natural variation. Stones, gravel, dead wood, and other structures that once slowed the water, created deep pools, rapids, spawning grounds, and sheltered habitats for fish and insects disappeared or were moved aside. As the river was straightened and simplified, much of the connection between the water and the riparian zones was also broken. What had once been a living and changing river became, along many stretches, more channelised, faster, and ecologically poorer.

In the summer of 2023, Rewilding Sweden began a multi-year effort to restore the ecological integrity of the upper Abramsån. By returning boulders, gravel, sand, and dead wood, variation is being recreated in the river. The water is slowed, the riverbeds become more diverse, and new habitats are formed where insect larvae, fish, plants, and other species can reclaim their place. Deep pools, rapids, and flood areas also help the river handle high flows in a more natural way. The goal is not to recreate Abramsån as it looked at one exact point in history. The goal is to give the river back its natural tools: structure, dynamics, and connection with the landscape. When the water is once again allowed to shape its own course, Abramsån can gradually rewild itself and contribute to a wilder and more living Råne river valley.

Funding: LOVA Swedish Agency for Marine and Water Management, Norrbotten County Administrative Board, EKOenergy

Prerequisites and rewilding approach

The challenge

Abramsån had long been affected by the requirements of timber floating. Even before the 1880s, the river was used to transport timber from state-owned forests onwards towards the Råne River and the coast, and in 1920 it became an official timber-floating route. To move timber efficiently, rapids were cleared, side channels were closed off, and the water was controlled with dams, flumes, brushwood structures, and timber cribs. On several flowing stretches, wooden structures were also built in the form of a timber floor in the channel to help the logs glide more easily, cutting off contact between the water and the natural riverbed. Together, these interventions created a straighter and faster river with far less variation, where stones, boulders, gravel, sand, and dead wood disappeared, were washed away, or were separated from the channel. The result was poorer spawning and nursery habitats for trout, reduced variation for benthic fauna and riparian plants, and worse conditions for the freshwater pearl mussel, which depends on young trout during its life cycle.

The solution

Phase 1: Restoring structural complexity

In the first phase, parts of Abramsån’s structural complexity were restored. Stones and boulders that had previously been cleared from the channel and placed along the banks were moved back into the river. Previously closed-off areas and side channels were opened where possible, and the river regained more variation in depth, bed substrate, and water velocity. The measures slowed the flow and created more current edges, pools, backwaters, holding places, and sheltered habitats. This improved conditions for trout, benthic fauna, riparian vegetation, and other species linked to flowing water. The restoration also helps more organic material and nutrients remain and circulate within the system, instead of being washed further downstream.

Phase 2: Adding fine-grained sediment sizes

In the second phase, the coarse restoration was complemented by adding finer sediment fractions, mainly sand, gravel, and smaller stones. After larger boulders and stones had been returned to the river, some stretches still had large gaps between the stones, where water could flow down through the bed structure instead of remaining in the visible channel. By adding sand and other finer material, these gaps were filled, helping to raise the water level, slow the flow, and create a more natural connection between water, riverbed, and riparian zone. The measure also had major ecological value, as many benthic fauna species depend on finer substrates such as sand and gravel. Together with the coarser structure, the finer sediments created a more varied riverbed environment, with better conditions for insect larvae, small crustaceans, mussels, fish fry, and other organisms in Abramsån’s flowing ecosystem. The addition of sand and gravel was funded by the EKOenergy Environmental Fund.

Expected response

We expect the ecosystem response to occur in three stages:

◆ Stage 1: Direct effects
Increased structural complexity; reduced flow velocity and greater variation in oxygenation; more dead wood and increased accumulation of organic material.

◆ Stage 2: Follow-on effects
Improved functional β-diversity among benthic invertebrates, caused by greater habitat variation; increased occurrence of leaf-shredding insects thanks to larger amounts of organic material; more species living in sand and gravel beds; stronger connections between aquatic and terrestrial ecosystems through increased water retention.

◆ Stage 3: Long-term goal, also influenced by other factors in the landscape
Increased fish occurrence in the rivers; richer birdlife along the banks as a result of more natural flooding and more swamp forest habitats.