Revision as of 10:06, 12 February 2014

Vääräjoki - Niskakoski

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Key features of the case study

Vääräjoki is a mid-sized lowland river with 835 km2 catchment area. The river is altogether 107 km long and descends 110 metres from its source to the confluence of the rivers Vääräjoki and Kalajoki.

Water quality of Vääräjoki is deteriorated due to human activities in the catchment. 12 % of the catchment area is in agricultural use. Also forestry activities, such as land draining by ditches, increase the nutrient load and suspended solids.

Site description

Drivers, Pressures, Measures

Altogether 25 km of Vääräjoki were channelized for flood protection and timber floating starting in 1860s and continuing in several occasions until late 1950s. In 1959-1974 lake Evijärvi at mid reach of Vääräjoki was dried for flood protection. Altogether 900 ha of lake area was dried by channelizing the river and by embankments. Especially the activities for flood protection changed the riffle areas considerably: the water retention capacity of the river bed decreased and the heterogeneous flow patterns in riffle habitats disappeared.

All the rapids in section from 13 km to 29 km of the river mouth have been restored. The extensive works started in the late 1990s and finished in 2006. The stream bottom was rearranged using boulders that had originally been removed from the channel during channelization and placed along stream margins Also gravel beds were created to provide nursery habitat for salmonids. The aim of the restoration was to return the heavily modified river closer to natural hydrological and morphological state and especially enable the breeding and migration of fish. Funding for restoration came from regional water and fisheries boards.

At the time of writing in Autumn 2013, there are plans to continue the restoration works at the other reaches: the restoration plan for upstream reach 35-86 km from river mouth is ready and the restoration work is about to begin. The plan to restore the downstream part of the river (0-13 km from the river mouth) is about to be ready.

The riffles in upper part of the river and downstream reaches of the river are yet not restored. Vääräjoki was chosen as a REFORM WP4 “flagship” case study river due to the extensive restorations and because it is among the few rivers in Finland that still had non-restored upstream control sites to meet the study design of WP4. Peurasaarenkoski is one of the channelized riffle sites and it is the non-restored control site in WP4 case study. Niskakoski is one of the restored riffle sections and it is the restored site in WP4 case study (Picture 1).

Measures selection

Success criteria

Ecological response

Hydromorphological response

Monitoring before and after implementation of the project

Before-after monitoring of the restoration success was not done. However, assessment of the ecological and water quality status of River Vääräjoki has been done after the restorations.

Socio-economic aspects

Contact person within the organization

Extra background information

References

Related Measures

• Improve water retention
• Add/feed sediment
• Shallow water courses
• Add sediments
• Initiate natural channel dynamics to promote natural regeneration
• Reduce impact of dredging
• Recreate gravel bar and riffles
• Lower river banks or floodplains to enlarge inundation and flooding
• Other measures

Related Pressures

• Sediment discharge from dredging
• Hydrological regime modification
• Artificial barriers upstream from the site
• Alteration of instream habitat
• Embankments, levees or dikes
• Channelisation / cross section alteration