Braided channels are fish-friendly

Posted on March 26, 2010

A braided channel takes the form of a mosaic of bars and multiple, interconnecting streams.  Braided channels occur in areas where there is a high supply of bed material, high stream power, low bank strength and a wide river valley.  They contain a multitude of locations where streams join or divide, and where as a result there is active sediment scouring and deposition.  This activity leads to a wide variation in channel depths, bottom sediments and flow patterns.  Such conditions, coupled with in-stream woody debris and vegetation, create a rich diversity of fish habitats, including shallow, flow-protected nursery areas.  Mathematical modelling of two Alpine rivers (the Tagliamento and Adige rivers inItaly) indicates that braided channels are much better than single-channel streams at preventing the washout of young fish.  At a distance of 1 km downstream of a spawning area, the retention of fish embryos and larvae was estimated at c. 10% for a braided stream, but less than 1% for an unbraided stream.  Over the last 100 years the amount of braiding in Alpine rivers has fallen dramatically due to human activities (e.g., land use changes, torrent control, dam construction, channelisation, sediment extraction), with negative implications for fish habitat diversity.

Reference:  Sukhodolov, A., Bertoldi, W., Wolter, C., Surian, N. & Tubino, M.  2009.  Implications of channel processes for juvenile fish habitats in Alpine rivers.    Aquatic Sciences 71, 338 – 349.