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| Titel |
Removal of small dams and its influence on physical habitat for salmonids in a Norwegian river |
| VerfasserIn |
Hans-Petter Fjeldstad, Bjørn Barlaup, Morten Stickler, Knut Alfredsen, Sven-Erik Gabrielsen |
| Konferenz |
EGU General Assembly 2010
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 12 (2010) |
| Datensatznummer |
250033102
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| Zusammenfassung |
| While research and implementation of upstream migration solutions is extensive, and indeed
often successful, full scale restoration projects and investigations of their influence on fish
biology are rare in Norway. Acid deposition in Norwegian catchments peaked in the 1980’s
and resulted in both chronically and episodically acidified rivers and Salmonids in River
Nidelva, one of the largest cathments in southern Norway, where extinct for decades. During
this period hydropower development in the river paid limited attention to aquatic ecology.
Weirs were constructed for esthetic purposes in the late 1970’s and turned a 3 km
stretch into a lake habitat, well suited for lake dwelling fish species, but unsuited for
migration, spawning and juvenile habitat for salmonids. Since 2005, continuous
liming to mitigate acidification has improved the water quality and a program for
reintroduction of Atlantic salmon has been implemented. We used hydraulic modeling to
plan the removal of two weirs on a bypass reach of the river. The 50 meters wide
concrete weirs were blasted and removed in 2007, and ecological monitoring has been
carried out in the river to assess the effect of weir removal. Topographic mapping,
hydraulic measurements and modeling, in combination with biological surveys
before and after the removal of the weirs, has proved to represent a powerful method
for design of physical habitat adjustments and assessing their influence on fish
biology. The model results also supported a rapid progress of planning and executing
of the works. While telemetry studies before weir removal suggested that adult
migration past the weirs was delayed with several weeks the fish can now pass the reach
with minor obstacles. Spawning sites were discovered in the old bed substrate and
were occupied already the first season after water velocities increased to suitable
levels for spawning. Accordingly, the densities of Atlantic salmon juveniles have
shown a marked increased after the conclusion of the project. Catches of pike and
cyprinids on the reach is reduced, indicating that their habitat is no longer suitable,
while salmon anglers have found new favorite spots in the restored pools and runs. |
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