Case study:HPP Blanca

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Location: 45° 59' 29", 15° 22' 53"
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Project overview

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Status Complete
Project web site
Themes Fisheries, Hydropower
Country Slovenia
Main contact forename HESS d. o. o.
Main contact surname HESS d. o. o.
Main contact user ID
Contact organisation HESS d.o.o.
Contact organisation web site
Partner organisations
Parent multi-site project
This is a parent project
encompassing the following
HPP Blanca and the fishway on the right part of the dam ( .

Project summary

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The fish pass on HPP Blanca is the first case of fish way on Sava river HPPs. It is located on the right part of HPP Blanca dam and constructed in the way of imitation of natural watercourse with hydrological characteristics, morphology, materials and varied habitat. The water level in the accumulation lake is changing for 1 m on the daily basis, which is why the inflow in fish pass has vertical slot pass with hydraulic barriers. Water velocity in the fish pass does not exceed 1 m/s. The flow is adjusted on fish migration and hydraulic scheme of the accumulation lake (

In order to bridge the differences in elevation, which is 9.4 m, the length of crossing is 680 m. Of these, 110 m of concrete section (intake facility on the upstream side) and 570 m of sustainable segment, in which also the culvert under a public road and drainage section is included (designed to attract fish). Water outflow from the fish pass itself attracts fish (

Monitoring surveys and results

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After the construction of HPP and fish way in 2009 the monitoring began and is still going on. The method used was electrical hunting and fish nets. In 2011 also telemetry was included in monitoring. Results showed that 32 of 40 fish in Sava river on the area of HPP Blanca was evidenced in the fish way (among them also Chrondrostoma nasus), since the beginning of the monitoring, which is good result.

The base for this project, which was done by IBE d. d., was interest in fish species composition in lower Sava river, the assessment of population size for each species, biological characteristics and ecological needs of species. Recommended guidelines and literature about fish passes were basis for the project scheme. The fish experts from Fisheries Research Institute of Slovenia were included in the project from the beginning, which is very good progress in cooperation between experts and energy producers. Even more progress can be done with founding the permanent monitoring of fish way function and maintenance (

Monitoring of fish in the fish pass.

Lessons learnt

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Image gallery

Fish pass after construction (Foto: HESS d. o . o. archive).
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Electrofishing (on the left) and sampling with fishing net (on the right) on Blanca HPP (photo: D. Zabric).

Catchment and subcatchment


River basin district Danube River Basin District
River basin Danube


River name Sava River
Area category 100 - 1000 km²
Area (km2)
Maximum altitude category 200 - 500 m
Maximum altitude (m) 270
270 m
0.27 km
27,000 cm
Dominant geology
Ecoregion Dinaric Western Balkan
Dominant land cover Wetland
Waterbody ID

Other case studies in this subcatchment: LIFE 06 NAT/SLO/000069 Intermittent Lake Cerknica


Name River Sava near settlement Blanca
WFD water body codes SI1VT739
WFD (national) typology
WFD water body name VT Sava Boštanj – Krško
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 No
Invasive species present No
Species of interest
Dominant hydrology Artificially regulated
Dominant substrate Gravel, Cobble
River corridor land use Extensive agriculture, Woodland
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 2009/01/01
Works started 2009/01/01
Works completed 2009/08/01
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 Fisheries Research Institute of Slovenia
Stakeholder engagement and communication
Works and works supervision
Post-project management and maintenance
Monitoring Fisheries Research Institute of Slovenia

Reasons for river restoration

Mitigation of a pressure Hydropower
Biology Fish: Species composition, Fish: Abundance, Fish: Disturbance-sensitive species, Fish: Age structure
Other reasons for the project


Structural measures
Bank/bed modifications New riverbed along old channel
Floodplain / River corridor
Planform / Channel pattern Creation of fish passes
Non-structural measures
Management interventions Monitoring strategy
Social measures (incl. engagement) Improved cooperation between energy producers and ecologists


Hydromorphological quality elements

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

Biological quality elements

Element When monitored Type of monitoring Control site used Result
Before measures After measures Qualitative Quantitative
Fish: Species composition Yes
Fish: Abundance Yes
Fish: Disturbance-sensitive species Yes
Fish: Age structure Yes

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

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

Monitoring documents

Additional documents and videos

Additional links and references

Link Description

Supplementary Information

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HESS d. o. o. Brežice. 2010. Prehod za vodne organizme na HE Blanca. Availabe at:

Zabric D. 2011. Prehodi za ribe pri HE Blanca – primer dobre prakse. Življenje vodi, str. 19–22. Availabe at:

Zabric, D. 2010. Ihtiološki pregled na HE Boštanj in HE Blanca - Monitoring ribje steze HE Blanca. / Ichtyological research at the HPP Boštanj and HPP Blanca – Monitoring of the fish migration aid at HPP Blanca. Report. Ljubljana.

Zabric, D., Jenic, A., Videmšek, U. 2012. Ihtiološki pregled na HE Boštanj in HE Blanca v letu 2012. / Ichtyological research at the HPP Boštanj and HPP Blanca in 2012. Report. Ljubljana.