A road culvert put in place too high which causes a migratory barrier in the watercourse.
Removal of migratory barriers
Connectivity is a crucial feature of aquatic ecosystems. The possibility for fish and other organisms to freely move between different parts of the water system is essential. Road culverts and manmade dams may form artificial barriers, preventing such movements. Thus, action is necessary to restore the connectivity watersheds. This will enable fish and invertebrate species to migrate within watercourses and in between lakes and streams, thus gaining mutual access to reproduction- and growth habitats that has been formerly inaccessible. These migrations increases reproduction and feeding possibilities and will enhance possibilities for species to maintain good population status in the area. This will re-establish the original biodiversity in the lake and stream habitats, stabilizing structure and function of the ecosystem. Fish species benefitting from this action are primarily lake dwelling brown trout and greyling reproducing in tributaries. Also recruitment of stream spawning coregonids will benefit as well as all fish species (cottids) and motile invertebrates in the watershed due to generally improved possibilities to freely move between different parts of the watershed. Increased brown trout densities and re-colonization of stream sections will enhance dispersal and recruitment of freshwater pearl mussels. Increased densities of fish populations in streams will benefit otter populations that, particularly during winter time when lakes are frozen over, need to find prey in running water. In the project area 17 road culverts that are barriers have been prioritized to be eliminated. At each site the specific conditions will determine which type of action that gives the best result. The improvement of road culverts will also give opportunities for otter to pass through the road culverts which minimize the risk of death by traffic.
Depending on conditions for the existing barrier the following possible actions can be undertaken in the project:
- The existing culvert will be changed to larger dimension.
- The existing culvert will be set to a lower level than present.
- The existing culvert will be complemented with sills and/or boulders downstream the culvert to raise the water level and thereby insure fish migration.
- The existing culvert will be changed in to an arch or bridge.
In the project area, 6 dams have been identified as significant barriers for fish and other organisms moving within streams and in and out of the lakes and will be removed or get a fish-way bypass. 4 of the dams are located in Billstaån, you can read more about subproject Billstaån here. The other two dams, are old, more or less demolished and not in use. They will be removed to improve connectivity.