Revision as of 09:43, 27 May 2014

Töss

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Site description

The Töss is a 56 km long river flowing in the north east of Switzerland. The river originates in the north east of the Swiss Alps, and forms the Töss valley. As well as the Thur river (flagship restoration measure), it is a tributary of the Rhine river which originates in the Swiss Alps and ends in the North Sea. The Töss is a pre-alpine river, without natural or artificial reservoirs along its course. The morphological conditions have been highly modified along its 56 km course. It contains numerous artificial weirs and embankments, constructed in the early 20th to protect cities against floods and provide more land for agriculture. Only the lower part of the river section, close to the connection with the Rhine River, is in good conditions, with almost natural morphology and pristine pool/riffle structure. To date, restoration efforts are made to restore, locally, a natural morphology within the river. The aim is to increase natural habitats, without to reduce water pumping efficiency for local citizens.

Measures selection

The Töss was restored in 1999 along a reach of 200 meters. The river was widened on both sides of the main river channel. Along the course of the river, embankments were removed to provide a large space to the river. Additional wood structure were added to enhance the ability of the river to recreate islands. Restoration efforts are expected to increase diversity of instream habitats and corresponding biota. To date, hydromorphological and biological indicators both suggest a lower increase in river quality and conditions after restoration compared to the restoration of the Thur (Flagship restoration measure). Socio-economic studies will complement ecological approaches, to assess the benefits or costs of restoration efforts. Moreover, long-term ecological studies will permit to guarantee the success of restoration. The Töss restoration is an interesting example of river restoration and management in Switzerland, providing information concerning restoration effects, and stimulating current and future studies.

Socio-economic aspects

Socio-economic studies will complement ecological approaches, to assess the benefits or costs of restoration efforts.

Extra background information

Link to project website:

http://www.awel.zh.ch/internet/baudirektion/awel/de/wasserwirtschaft/bauen_am_und_im_Wasser/neues_gewaesserschutzgesetz/umsetzungsprogramm/teilprojekt2_revitalisierung.html

References

Related Measures

• Establish environmental flows / naturalise flow regimes
• Facilitate downstream migration
• Remove barrier
• Widen water courses
• Allow/increase lateral channel migration or river mobility
• Remeander water courses
• Initiate natural channel dynamics to promote natural regeneration
• Remove sediments
• Remove bank fixation
• Remove or modify in-channel hydraulic structures
• Lower river banks or floodplains to enlarge inundation and flooding
• Remove hard engineering structures that impede lateral connectivity
• Construct semi-natural/articificial wetlands or aquatic habitats
• Set back embankments, levees or dikes

Related Pressures

• Groundwater abstractions
• Artificial barriers downstream from the site
• Artificial barriers upstream from the site
• Alteration of instream habitat
• Embankments, levees or dikes
• Loss of vertical connectivity
• Alteration of riparian vegetation
• Channelisation / cross section alteration