Author(s): Susana Dias Amaral, Paulo Branco, Teresa Ferreira, Jose Maria Santos, Christos Katopodis, Antonio Pinheiro

Linked Author(s): Paulo Branco, Maria Teresa Ferreira, José Maria Santos, Christos Katopodis, António Pinheiro

Keywords: Potamodromous cyprinid species; Low-head ramped weirs; Upstream migration; Ecohydraulics;

Abstract: Low-head ramped weirs are one of the most common small engineered structures present in Iberian rivers. Fish passability of these obstacles, where water passes over but does not generate a waterfall, is primarily related to ramp length and slope. However, the relative contribution of these factors has seldom been investigated. This study aims to assess the upstream passage performance of a medium-size potamodromous cyprinid, the Iberian barbel (Luciobarbus bocagei), negotiating an experimental low-head ramped weir with varying ramp length (L), slope (S), and discharge (Q). A total of 4 configurations were initially tested contemplating different combinations of L (1.50, 3.00 m) and S (10, 20, 30 %), with a constant Q of 110 L.s-1. The configuration with the lowest number of successful upstream passages was then assessed for an additional Q of 55 L.s-1. Results suggest that both factors L and S, as well as Q, influenced passage performance of fish. While attraction efficiency increased with increasing L and S, the number of successful negotiations, and consequently passage efficiency, decreased upon increasing L, and peaked at the intermediate value of S. Regarding Q, although its reduction contributed to the presence of a smaller water column on the ramp, the number of successful passages increased significantly. However, both attraction and passage efficiencies registered lower values, suggesting that it is rather difficult to determine the most suitable combination of hydrodynamic conditions downstream and over the ramp for efficient fish passage. These results may be useful for designing appropriate passage structures for low-head instream obstacles.

DOI: https://doi.org/10.3850/38WC092019-0624

Year: 2019