Upstream passage of Potamodromous Cyprinids over small weirs: the influence of key-hydraulic parameters

Abstract

The presence of small weirs, far more numerous than dams, has increased habitat fragmentation on rivers worldwide. This study aims to evaluate the upstream passage performance of a potamodromous cyprinid, the Iberian barbel (Luciobarbus bocagei), over an experimental broad-crested weir by varying key-hydraulic parameters. Fish passage success was studied for different combinations of waterfall height (Dh), plunge pool depth (D) and flow discharge (Q). The flow pattern downstream of the weir was characterized with a 3D Acoustic Doppler Velocimeter, to assess the effects of hydrodynamics on fish behaviour. D, Dh, and their interaction D £ Dh as well as Q were correlated with the number of successful upstream fish passes. However, counter-intuitively, higher fish passage success did not occur at combinations of lower Dh and Q, and higher D. Therefore, upstream fish passage appears to be a complex phenomenon, which is strongly dependent on the hydraulic environment that is produced by the interaction of these parameters. The outcomes of this work will help engineers and biologists to establish design criteria for requalification of small barriers in order to improve fish passage and habitat connectivity.