Case study:Blanice River

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Location: 49° 7' 20.58" N, 14° 5' 27.13" E

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Project overview

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Status	Complete
Project web site
Themes	Hydromorphology
Country	Czech Republic
Main contact forename	Petr
Main contact surname	Hartvich
Main contact user ID
Contact organisation
Contact organisation web site	http://www.prf.jcu.cz/en/
Partner organisations	University of South Bohemia
Parent multi-site project
This is a parent project encompassing the following projects	No

The bypass under construction. Depositing of boulders on the banks and into the sill across the stream. (V. Šámal)

Project summary

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Initial conditions The Blanice River springs at 972 m above sea level in the Šumava Mountains and joins the Otava River at an elevation of 362 m, where it is characterised as a lowland river with remaining oxbows. The gradient of the 93.3 km long river is 5.15% and the average flow is 4.23 m3.s-1 at its lower end.

Many damming-up devices have been built for water mills, hammer mills and sawmills, increasing the need for water. The river was fragmented into parts with still water and parts where the flow was regulated. The character of the river ecosystem has changed, affecting the natural development of fish populations (Hartvich et al. 2004). A high dam works as a migration barrier. It cannot be overcome by fish moving upstream and so the long-term loss of upstream migration negatively influences the exchange of genetic information during reproduction. Separated fish populations become smaller as well as less resilient. Fish which are flushed downstream by the flow cannot get back to their habitat (Peter 1998, Lucas & Baras 2001). Therefore fish passes are built where damming-up devices (weirs etc.) are located. They allow fish and other aquatic animals to pass the barriers and move freely along the river. Fish passes transfer the backwater to the stream below the barrier and are either a part of the migration barrier or placed on the grounds next to the barrier. In this case the fish pass functions as the bypass of a barrier. These fish passes are built in such a way that their character, structure and stream flow are similar to the conditions of natural rivers (Kubečka et al. 1997, Cowx & Welcomme 1998, Gebler 2009, Lusk et al. 2011). In total 17 fixed or mobile barriers (weirs, dams) are placed across the Blanice River. These barriers are not migration-permeable, with one exception. The river continuity is disrupted mainly by the Husinec Dam-lake (area 61 ha, backwater 3.5 km long, maximum 25.5 m deep). Below the dam, the river has a weir impassable for migrating aquatic animals. On the right bank a ground overgrown with deciduous trees and a part of a former oxbow connected to the river below the weir were available. Because of these conditions, a near-natural bypass was proposed as the most convenient solution.

Objectives Restoring and preserving healthy populations and diversity of the original fish species in Blanice River by means of building a bypass.

Restoration measures In 2002, a 35 m long bypass was built at the weir to allow upstream migration. It runs from the upper weir through natural terrain around the body of the weir and joins the river 20 metres downstream of the weir. The average gradient is 5%. Fig. 3 shows the placement of this near-natural bypass. At a medium flow rate (Q180), up to 250 l.s-1 flows through the bypass. The 2.5 m wide upper part of the bypass is a torrent fish pass with an inlet device placed upstream of the weir. The construction includes 9 stone sills for the necessary backwater, in which 7 to 16 cm wide gaps between the stones (boulders) enable fish to swim through either at the bottom or below the water surface. Gravel and smaller stones on the bottom decrease the flow in the lower water layers. The sills differ no more than 15 cm in height and their depth ranges from 0.3 to 0.5 m. The lower part of the bypass is formed by the oxbow (which was first cleaned) with slowly flowing waterThe width of the low

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Catchment and subcatchment

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Catchment

River basin district	River Elbe
River basin	River Elbe

Subcatchment

River name	Blanice River
Area category	100 - 1000 km²
Area (km2)	543.3543.3 km² <br />54,330 ha <br />
Maximum altitude category	500 - 1000 m
Maximum altitude (m)	972972 m <br />0.972 km <br />97,200 cm <br />
Dominant geology
Ecoregion
Dominant land cover
Waterbody ID

Site

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Name	Blanice River
WFD water body codes
WFD (national) typology
WFD water body name
Pre-project morphology	Low gradient passively meandering
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	No
Species of interest	brook lamprey (Lampetra planeri), crayfish
Dominant hydrology
Dominant substrate
River corridor land use	Improved/semi-improved grassland/pasture
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)	4.234.23 m³/s <br />4,230 l/s <br />
Average channel gradient category
Average channel gradient	0.0515
Average unit stream power (W/m2)

Project background

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Reach length directly affected (m)	60006,000 m <br />6 km <br />600,000 cm <br />
Project started	2002/01/01
Works started	2002/01/01
Works completed	2002/12/31
Project completed
Total cost category	10 - 50 k€
Total cost (k€)	1992019,920 k€ <br />19,920,000 € <br />
Benefit to cost ratio
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Cost for project phases

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Reasons for river restoration

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Mitigation of a pressure	Impoundments (not hydropower)
Hydromorphology	Continuity of sediment transport, Channel pattern/planform
Biology	Fish
Physico-chemical
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Measures

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Floodplain / River corridor
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Monitoring

Hydromorphological quality elements

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quality elements

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Supplementary Information

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