Case study:Restoration of the River Paasonjoki

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Location: 66° 5' 44.69" N, 27° 22' 33.29" E

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Project overview

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Status	Complete
Project web site
Themes	Fisheries, Habitat and biodiversity, Hydromorphology
Country	Finland
Main contact forename	Jarmo
Main contact surname	Huhtala
Main contact user ID	User:Kasvio
Contact organisation	Centre for Economic Development, Transport and the Environment for Lapland
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project encompassing the following projects	No

The River Paasonjoki after the restoration (photo J. Huhtala)

Project summary

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The River Paasonjoki is 4 930 meters long and it flows though forest areas from the Lake Paasonjärvi to the Lake Yli-Soppanajärvi. The catchment area is 97,92 km2. The river bed is mainly sand and contains rocks and gravel. A big part of the river is marked as nature conservation area. The water quality in the river is good or very good.

The Centre for Economic Development, Transport and the Environment for Lapland restored four sections in the River. The restoration was made to improve the living conditions of the fish and other species. Rocks and gravel was placed to the river to make rapid areas more suitable for the trouts to reproduce. The aim of the retoration was to improve the living conditions of migratory fish and to make the river more nature-like and closer to its natural state. Trouts, grayling and macro invertebrates will benefit from the restoration and not only in the river but also in the nearby lakes. The rivers in the area are straightened for log floating since 1900 century. Also the natural state in the rivers are altered because of intense forestry and bog drainage.

The restoration plan was accepted 4.3.2011 and the work started immediately. The plan was restore six rivers in the area. The area is highly appreciated among the fly fishers and its very popular recreational area.

The restoration plan aimed to slow down the current and produce suitable nesting habitats for the trouts and shelter places for the juveniles. Also versatility to the river bed was improved by digging few wider areas. Gravel was brought approximately 40 m3 and placed to the river in several places bed to ensure the nesting habitats for the migratory fish. Before the restoration many stones were taken away from from the river and places a side of the river. All the stones that were piled up next to the river were used in the restoration work.

Also in the section three, the channel curve was altered in few places so that the erosion that occured in the channel would be protected from further erosion. Also in the section four the river was made more curvy to reduce the erosion in the channel and to protect the sand from accumulating to the river bed.

The lenght of the first restored area is 430 meters and the width is 4,3 in average. The restored rapid area in the totally was 1900 m2. The Second was 540 meters long, width 6 meters and the area in total was 3 240 m2. The thirds section was 300 meters, width 6 meters and the area was 1 800 m2. The last section was 570 meters long, width 8 meters and the total area reached up to 4 560 m2. The elevations difference in the restored area was 18 meters.

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Image gallery

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The River Paasonjoki before the restoration (Photo Huhtala)

Catchment and subcatchment Select a catchment/subcatchment Site Edit site Name WFD water body codes WFD (national) typology WFD water body name Pre-project morphology Reference morphology Desired post project morphology Heavily modified water body No National/international site designation Local/regional site designations Protected species present Yes Invasive species present Yes Species of interest Brown trout (Salmo trutta), Brook trout, grayling (Thymallus thymallus) Dominant hydrology Dominant substrate River corridor land use Average bankfull channel width category 5 - 10 m Average bankfull channel width (m) Average bankfull channel depth category Average bankfull channel depth (m) Mean discharge category Mean annual discharge (m3/s) Average channel gradient category Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) Project started Works started Works completed Project completed Total cost category Total cost (k€) Benefit to cost ratio Funding sources Cost for project phases Phase cost category cost exact (k€) Lead organisation Contact forename Contact surname Investigation and design Stakeholder engagement and communication Works and works supervision Post-project management and maintenance Monitoring Reasons for river restoration Edit reasons for restoration Mitigation of a pressure Hydromorphology Channel pattern/planform, Width & depth variation, Flow velocities Biology Fish, Invertebrates Physico-chemical Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Floodplain / River corridor Planform / Channel pattern Other Non-structural measures Management interventions Social measures (incl. engagement) Other Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Physico-chemical quality elements Edit Physico-chemical quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Any other monitoring, e.g. social, economic Edit Other responses Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description Supplementary Information Edit Supplementary Information