Difference between revisions of "Emån - Emsfors"
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Revision as of 15:53, 12 February 2014
Emån - Emsfors
Key features of the case study
In the following section, background and motives of the restoration project which led to the initiation of the project are introduced.
Drivers and Pressures
River Emån has historically been an important reproduction site for Baltic salmon and sea trout. Extensive exploitation of the river for hydropower production in the 20th century has however created numerous barriers for migrating fish in the form of hydropower dams and substantial fragmentation of the river network. Hydropower dams are moreover typically constructed in river sections were the stream gradient is high and the damming of riffles and rapids results in a loss of habitat for salmonid fish. The hydropower dam at Emsfors used to be the first barrier in the river (located ca. 4 km from the sea). There was an old fish ladder at the hydropower dam but this had limited functionality and it was estimated that only ca 50 % of spawning migrating salmonid fish would pass through the fishway. Other fish species such as whitefish (Coregonus sp.), ide (Leuciscus idus) and wels catfish (Siluris glanis) could not pass the dam.
Timber floating has been an important activity in the River Emån catchment until the 1960s. To facilitate the downwards transport of timber, narrow shallow sections of the river were deepened and boulders were removed. This has created a more homogenous bottom structure and more homogenous flow in these river sections and reduced their suitability as spawning areas and habitat for salmonid fish.
The lower reaches of River Emån are surrounded by extensive floodplains, periodically flooded wetlands, grasslands, pastures and forests. The river section is considered as one of the most important localities for wels catfish in northern Europe. Catfish migrate into the flooded riparian habitats to forage for food and to spawn. In the 20th century large scale ditching campaigns transformed many of these floodplain areas into arable land and dikes were constructed to prevent flooding. This has reduced the habitat for wels catfish. In the Emsfors region the floodplains are still relatively undisturbed and large areas surrounding the river are periodically flooded.
Global objectives
The main goal of the restoration project was to restore the Emsfors area in the lower reaches of River Emån to near natural conditions. Restoration of lateral connectivity and habitat improvement at Emsfors was expected to improve the potential for natural reproduction of Baltic salmon and sea trout in the river and would help to secure the populations long term survival. Other animal groups that were expected to benefit from the restoration included the European eel (Anguilla Anguilla), European river lamprey (Lampetra fluviatilis), asp (Aspius aspius), wels catfish, thick shelled river mussel (Unio crassus) and fresh water pearl mussel (Margaritifera margaritifera). The restoration was deemed important and in line with the conservation plans for two Natura 2000 areas in the River Emån catchment (“Emåns vattensystem i Kalmar län, SE0330160” and “Våtmarker längs Emåns nedre lopp, SE033173”) and for the long term conservation status of the habitat type “Fennoscandian natural rivers, 3210” according to the EU Habitats Directive.
Specific goals
- To restore lateral connectivity at Emsfors the Emsfors hydropower dam was to be completely removed. A fishway with a low inclination for fish species that “are less prominent swimmers” should also be constructed to create “exceptionally good conditions for fish migration” at the site.
The head of Emsfors hydropower dam was concentrated to the area 200 m upstream from the dam. Hydrological modeling, with the retention water level of the hydropower dam as a starting point, did however reveal that a removal of Emsfors hydropower dam could cause a substantial drop in water level a long distance upstream from the dam at low flows. The water level would remain relatively unchanged at high flows. There was concern that a drop in water level could damage important floodplain habitats in this area. This could also have a negative impact on the catfish population. This concern emanated in a secondary goal of the restoration project.
- Threshold areas/riffles upstream from Emsfors hydropower dam, that had been deepened to facilitate timber floating, should be restored to reduce the drop in water level upstream from the dam at low flows after dam removal and to protect the flood plain habitats in this area. The threshold areas/riffles suitability as spawning areas and habitat for salmonid fish was also expected to be improved by the restoration.
Site description
No information found.
Measures selection
Success criteria
Ecological response
Hydromorphological response
Monitoring before and after implementation of the project
Socio-economic aspects
Contact person within the organization
Extra background information
References
Related Measures
- Establish environmental flows / naturalise flow regimes
- Increase flood frequency and duration in riparian zones or floodplains
- Remove barrier
- Facilitate downstream migration
- Recreate gravel bar and riffles
- Shorten the length of impounded reaches
- Install fish pass/bypass/side channel for upstream migration
