Case study:Renaturation of Stržen's riverbed on intermittent Cerknica Lake

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Location: 45° 44' 52.48" N, 14° 22' 57.90" E

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Project overview

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Status	In progress
Project web site	http://life.notranjski-park.si/en/
Themes	Environmental flows and water resources, Habitat and biodiversity, Hydromorphology, Social benefits
Country	Slovenia
Main contact forename	Irena
Main contact surname	Likar
Main contact user ID
Contact organisation	Notranjska Regional Park
Contact organisation web site	http://www.notranjski-park.si/en
Partner organisations	Institute of the Republic of Slovenia for Nature Conservation, The Fisheries Research Institute of Slovenia, DOPPS – BirdLife Slovenia
Parent multi-site project
This is a parent project encompassing the following projects	No

View of the project area. Stržen's riverbed (straight channel and former meanders) is visible in the top half of the photo.

Project summary

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The main objective of the LIFE STRŽEN project is to improve the conservation status of the Habitats Directive priority habitat, Turloughs, by restoring the former Stržen riverbed. The watercourse will be prolonged by 1.5 km. This will have several positive effects, including an increased saturation of soil with water that will improve conditions for characteristic species of fish, invertebrates, birds and mammals. The project also aims at reducing the negative impact of visitors on the restored riverbed area and establishing quiet zones in the breeding habitat of the Eurasian bittern (Botaurus stellaris) in order to improve its breeding success. A further aim is to gain long-term support for its conservation actions among the general public, and a positive change of attitude among key stakeholders. Thus, the objectives are strongly linked to the EU Habitats and Birds directives, Biodiversity Strategy 2020, and Water Framework Directive.

Funding - EU Contribution: € 2,863,212.00

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Image gallery

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Arrival of mechanisation at the entry to the lake

Excavators are waiting at the entry to the lake for suitable conditions to start work

Preparation of access roads proved to be tricky due to rainfall.

Due to the wet terrain we had to strenghten the access road with gravel.

In 2020, unfortunately the works could not continue due to high water levels.

Making a new access road over the straight channel to land inside the meander.

Before we could start filling in the straight channel, we had to rescue any fish and crustaceans and pump out as much water as possible, so the soil wouldn't turn to mud.

After rescuing as much fish and crustaceans as possible, the construction crew started filling in the channel with soil they had dug out two years back.

Part of the channel is finally filled up with soil.

The straight channel was being filled in from both sides with excavators.

Progress in filling in the now-dry straight channel.

First layer of soil is in the straight channel

The final part of the lower part of the channel is being filled in - this was the trickiest part, since it was very muddy.

Making of the third barrier at the crossing of the renewed meander and straight channel.

Catchment and subcatchment Select a catchment/subcatchment Edit the catchment and subcatchment details (affects all case studies in this subcatchment) Catchment River basin district Danube River basin Danube Subcatchment River name Sava River Area category more than 10000 km² Area (km2) Maximum altitude category 500 - 1000 m Maximum altitude (m) 833833 m <br />0.833 km <br />83,300 cm <br /> Dominant geology Calcareous Ecoregion Dinaric Western Balkan, Alps Dominant land cover Waterbody ID Other case studies in this subcatchment: Conservation of alluvial, Hainburg River Restoration, INTERREG MED WETNET - Memoradum on Participation in Wetland Conservation in Ljubljansko Barje Nature Park, Marsh protection in Egyek–Pusztakócs, National Park Danube-Auen, Regelsbrunner Aue, Renaturation of Stržen's riverbed on intermittent Cerknica Lake, The Bulgarian Wetlands Restoration and Pollution Reduction Project, Witzelsdorf Pilot Project Site Edit site Name Watercourse Stržen on intermittent Cerknica Lake WFD water body codes SI141VT2 WFD (national) typology Class III - Slightly Modified Rivers, JDP WFD water body name VTJ Cerkniško jezero - Stržen Pre-project morphology Artificial channel, Straightened Reference morphology Sinuous - original natural riverbed (double meander) Desired post project morphology Sinuous - double meander, Low gradient passively meandering Heavily modified water body No National/international site designation All - multiple designations across the site Local/regional site designations Regional Park – protected area Protected species present Yes Invasive species present No Species of interest Great Bittern (Botaurus Stellaris), Common snipe (Gallinago gallinago), Spotted crake (Porzana porzana), Little Crake (Porzana parva), Marsh Harrier (Circus aeruginosus), Ruff (Philomachus pugnax) Red-necked grebe (Podiceps grisegena), Great white egret (Ardea alba), Purple heron (Ardea purpurea), Savi's warbler (Locustella luscinioides), Water rail (Rallus aquaticus), Great reed warbler (Acrocephalus arundinaceus), Northern shoveler (Anas clypeata), Ferruginous duck (Aythya nyroca), Wood Sandpiper (Tringa glareola), Italian crested newt (Triturus carnifex), Otter (Lutra lutra), Lesser Ramshorn Snail (Anisus vorticulus)… Dominant hydrology surface water hydrology, Groundwater Dominant substrate Earth, ice-age clay deposits, Peat River corridor land use Wetland, Rough unimproved grassland/pasture Average bankfull channel width category 10 - 50 m Average bankfull channel width (m) Average bankfull channel depth category 0.5 - 2 m Average bankfull channel depth (m) Mean discharge category 10 - 100 m³/s Mean annual discharge (m3/s) 10.910.9 m³/s <br />10,900 l/s <br /> Average channel gradient category Less than 0.001 Average channel gradient Average unit stream power (W/m2) Project background Edit project background Reach length directly affected (m) 15001,500 m <br />1.5 km <br />150,000 cm <br /> Project started 2017/09/01 Works started 2019/07/21 Works completed 2021/09/30 Project completed 2023/12/31 Total cost category 1000 - 5000 k€ Total cost (k€) 38633,863 k€ <br />3,863,000 € <br /> Benefit to cost ratio Funding sources European Union, Slovenian Ministry for environment and spatial planning, Municipality of Cerknica, Ebmpapst d.o.o., Elgoline d.o.o., Alpod d.o.o. 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 Land drainage Hydromorphology Quantity & dynamics of flow, Width & depth variation Biology Fish, Invertebrates Physico-chemical Temperature, Oxygen balance, Nutrient concentrations Other reasons for the project Measures Edit Measures Structural measures Bank/bed modifications Riverbed restoration Floodplain / River corridor Establishing of quiet zones Planform / Channel pattern Re-instatement of old course – double meander Other Non-structural measures Management interventions Quiet zone establishment (fishing is forbiden, visiting discouraged), plan for quiet zone management, Mowing management Social measures (incl. engagement) Education of youth – admission-free field trips, ornithological camps, creative competitions; Active communication with key stakeholders – landowners, hunters, fishermen and tourism providers; Education of tourism providers. Other Popularization of the project; information provision – project website, Information Bulletins, social media etc. Monitoring Hydromorphological quality elements Edit Hydromorphological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Channel pattern/planform Yes Yes No No Yes Improvement Flow velocities Yes Yes No No No Improvement Quantity & dynamics of flow Yes Yes No No Yes Improvement Width & depth variation Yes Yes No No No Improvement Biological quality elements Edit biological quality elements Element When monitored Type of monitoring Control site used Result Before measures After measures Qualitative Quantitative Macrophytes Yes Yes No No Yes Improvement Macrophytes and/or phytobenthos: Taxonomic composition Yes Yes No No Yes Improvement Macrophytes and/or phytobenthos: Average abundance Yes Yes No No Yes Improvement Invertebrates Yes Yes No No Yes Improvement Invertebrates: Abundance No No No No No Improvement Invertebrates: Diversity Yes Yes No No Yes Improvement Invertebrates: Taxonomic composition Yes Yes No No Yes Improvement 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 PH Yes Yes No No Yes Improvement Temperature Yes Yes No No Yes No change Oxygen balance Yes Yes No No Yes Improvement 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 Habitat mapping Yes Yes No No No Improvement Monitoring documents Upload monitoring documents Additional documents and videos Upload additional documents Additional links and references Edit links and references Link Description http://ec.europa.eu/environment/life/project/Projects/index.cfm?fuseaction=search.dspPage&n proj id=6296#EI European Commission article about the project http://life.notranjski-park.si/en/ Official project website (English) Supplementary Information Edit Supplementary Information