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Mader, H., G. Unfer and S. Schmutz (1998). The effectiveness of nature-like bypass channels in a lowland river, the Marchfeldkanal. Pages 384-402 in M. Jungwirth, S. Schmultz and S. Weiss, eds. Fish Migration and Fish Bypasses, Fishing News Books, Vienna (Austria).

We investigated the effectiveness of two nature-like bypass channels in a lowland river, the Marchfeldkanal (MFK), a man-made side channel of the Danube river. The flow of the MFK is controlled by several weirs, each circumvented by a fish pass consisting of a sequence of nature-like pools connected by flumes. Physical conditions were measured in the bypasses and at the entrances across varying discharges. Fish passage was recorded using traps during spring and early summer from 1993 to 1995. Electrofishing samples in the pools below the weirs, and in a stretch of the canal below the lowermost weir, were compared with the species composition found in the traps. Flow experiments showed that the most efficient bypass channel discharge is about 0.25 m²u³/s, which provides both large cross-sectional areas with low flow velocities and high water depths within the flumes. There was no significant correlation between attraction flow (412% of the MFK mean flow) and fish passage. From 1993 to 1995 more than 150,000 individuals of 40 species passed the bypass channels. Species composition was dominated by so-called 'non-migratory' small-sized species; juvenile fish comprised 14% of the catch. Comparing species composition below the weirs with passage provided a useful tool to assess species-specific efficiency of the bypass. This study proved the effectiveness of two nature-like bypass channels in a lowland river for almost all occurring species and lifehistory stages.