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Återställning av älvar som använts för flottning : en vägledning för restaurering
- 2007
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Samlingsverk (redaktörskap) (övrigt vetenskapligt/konstnärligt)abstract
- These guidelines describe the history of timber-floating principally referring to the period from the early 1800s to the 1980s. Timber-floating was essential for transporting timber to the coast and timber processing industries. It was carried out in small as well as large rivers. At the turn of the century (1900) there were for example, more than twice as many floatways in the provinces of Norrbotten and Västerbotten than were there railways and roads. To make transport more efficient, rivers were successively rebuilt to become more and more like canals. This was done by constructing for example dams, flumes, excavated canals, and various piers. The canalization of rivers implied a simplification of their morphology. In multibranched reaches all channels were cut off except the one that was used for timber floating, wide rapids were narrowed, and boulders and stones were removed from the channel. This led to an increase in current velocity and sediment transport. Simultaneously, ice conditions became worse with more and more anchor ice. Many riparian areas were separated from the river channel and their production decreased. The aquatic habitats were deprived of nutrients and their animal life changed. Simuliid larvae were favoured but most other animals lost habitats and became rarer. Lotic fish were affected in several ways, for example their migration, spawning, food searching and protection were reduced. Restoration of rivers used for floating may, aside from funding require a large organization. Before any practical work can commence, objects must be inventoried and permission granted. Therefore, work needs to be contracted and planned and workers trained. Since many floatway objects have cultural and historical values and single landowners may oppose restoration, consultation and support are needed. A basic part of the restoration work consists of opening closed channels and removing dams and piers and spreading their material over the bottoms. Trees grown on piers are also placed in the water. In addition, fish spawning areas are restored using specific methods. When objects are technically complicated or difficult to access, or protected for cultural and historical or nature conservation reasons, they can be left completely. There is an idea that restored rivers will automatically return to their previous state. This is not the case. Therefore, it is important to follow up what happens after a restoration, not the least to develop restoration methods and to correct already completed restorations. In the report, several examples are given on various followup methods.
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