Case study:Onga River

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Location: 58° 50' 30.48" N, 26° 24' 14.49" E

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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
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Contact organisation web site
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Parent multi-site project
This is a parent project encompassing the following projects	No

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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 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 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 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 Biology 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