Case study:Onga River

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Location: 58° 50' 30", 26° 24' 14"
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Project overview

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Status Complete
Project web site
Themes Fisheries, Habitat and biodiversity, Hydropower, Water quality
Country Estonia
Main contact forename Kesler
Main contact surname Martin
Main contact user ID User:Kasvio
Contact organisation
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Partner organisations
Parent multi-site project
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encompassing the following
projects
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Project summary

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The Onga River is the biggest tributary of the Pedja River in the upper course. It is located in Lääne-Viru and Jõgeva counties. The length of this river is 30 km and its catchment area is 109 km2. The upper course of the river is located on the Pandivere Highlands, the middle course on the Alutaguse lowlands and the lower course is located in the north of Vooremaa.

In the summers of 1988 and 1994, The Onga Rivers water was slightly alkaline: in 1988, the pH value was 7,8 in the middle course of the river and 8,0 in the lower course of the river, and in 1994, the pH value was 7,7. There is no data about the mineral content of the water. The total content of organic matter in the water was low in Juny 1988 in the middle course of the river and medium in the lower course. In July 1994, the same figure was very low in the lower course of the river.

There is no literature data regarding which fish species can be found in the Onga River. Results for test catches in 1988 showed 6 different fish species. These species were: minnow, bullhead catfish, pike, burbot, loach and stickleback. The Onga River with its cold water which mostly comes from springs, is considered a trout river.

Recent work that has been done on the river: the clearing of sediments from the Onga River, the construction of sedimentation tanks on the river and bigger dicthes, the clearing of shores from fallen trees, if necessary, opening old river beds, fixing up drain oulets, slope fixing with rocks, fixing up a bridge, rapids in the streambed, placing rocks and groups of rocks, spawning beds for brown trots, construction of fish ladder and extension of the river bed for the dam at the Selli mill, construction of winter areas for fish and bringing the Selli biological treatment plant into order.

The construction took place on a 15,5 km distance on the Onga River. It started in October 2010, ended in October 2011 and the cost of it was 326 000 euros.

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Catchment and subcatchment



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 Yes
National/international site designation
Local/regional site designations
Protected species present Yes
Invasive species present Yes
Species of interest minnow, pike, burbot (Lota lota), stickleback
Dominant hydrology
Dominant substrate
River corridor land use
Average bankfull channel width category
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

Reach length directly affected (m)
Project started 2010/10/01
Works started
Works completed 2011/10/01
Project completed
Total cost category
Total cost (k€) 326
326 k€
326,000 €
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

Mitigation of a pressure
Hydromorphology
Biology
Physico-chemical
Other reasons for the project


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

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative

Biological quality elements

Element When monitored Type of monitoring Control site used Result
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Physico-chemical quality elements

Element When monitored Type of monitoring Control site used Result
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Any other monitoring, e.g. social, economic

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Monitoring documents



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Supplementary Information

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