Klebach - Side channel

Klebach - Side channel

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Site description

The Drava river (also known as Drau river in German) is a 6^th order stream. At the project site, in the Upper Drava Valley, it forms the boundary between the Crystalline of the Central- and the Limestone Alps. The site of the project is located near the village of Klebach in Austria. From this point onward the Drava has a discharge basin of roughly 2500 km². The average flow of the river near the site is 76m³/s. The river at the site was historically braided with gravel banks in the channel. The Drava river has been largely regulated from the 1930 onward in the area. Banks were fixated and meanders straightened out. Lateral connection with the floodplains and side arms was removed and these areas found new use as agricultural or forestry lands. In-channel gravel banks were removed artificially or through the changes in hydrology caused by the other alterations to the river. Downstream of the side a number of hydro-power plants were constructed, these significantly disrupted longitudinal connectivity of the river. At the same time these plants do produce 'green' energy for large parts of the surrounding areas.

Measures selection

The Waterauthority of the province of Carinthia in Austria, in an effort to restore some of the natural regime and ecology of the Drava, dug a side channel near the village of Klebach. This side channel was situated on the right hand side of the river in what was formerly agricultural land. On the left hand side groins were erected in hopes of keeping the entrance to the side channel open. Also, these groins were meant to initiate morphological variability in the river. The side channel itself was more then 300m in length and was originally build in two parts. This means that water was also able to enter/exit the channel about half way along it, creating what is best described as an artificial attempt at a braided river. The island that was created by the measure was the remainder of the old river bank with its old vegetation still intact.

Success criteria

The aims of the project were to:

• stop degradation
• initiate a changing river morphology
• diversify the spatial variability of flow velocity and sediment grain sizes
• restore an ecologically sound environment (in the form of habitat structures)

Ecological response

Macrophytes and phytobenthos

Not monitored

Benthic invertebrates

The benthic invertebrates were measured in the main and in the side channel. Due to lower shear stresses in the side channel the invertebrates had both higher population densities and species diversity than in the main channel. Part of this was also attributed to algal growth in the side channel which served as a habitat for the benthic invertebrates.

Fish

Fish species were shown to have significantly higher population densities in the side channel. The side channel was shown to serve as a hatching ground for many fish species. Also, two rheophilic fish species were found at the site, indicating it as an important spawning ground for rheophilic species. Despite these positive effects long term analysis has shown that the fish ecological status is still labelled as Poor by WFD standards. None the less, it has improved compared to the parts of the river where no restoration has taken place. One of the reasons for the Poor status of the area may be related to the scale of the measure compared to the pressures influencing the river. The downstream hydropeaking and longitudinal disruption of the connectivity remain unaltered by the local measure of the side channel.

Contact person within the organization

Wasserwirtschaft Kärnten e-mail, Tel.: 050 536-31802 _(Austria)

Related Measures

• Increase flood frequency and duration in riparian zones or floodplains
• Shorten the length of impounded reaches
• Remove bank fixation
• Recreate gravel bar and riffles
• Remove or modify in-channel hydraulic structures
• Remove bank fixation
• Reconnect backwaters and wetlands
• Construct semi-natural/articificial wetlands or aquatic habitats

Related Pressures

• Hydrological regime modification
• Hydropeaking
• Artificial barriers downstream from the site
• Impoundment
• Channelisation / cross section alteration
• Alteration of riparian vegetation
• Alteration of instream habitat
• Embankments, levees or dikes
• Sand and gravel extraction
• Loss of vertical connectivity