Effects of the Diversity of Flow Velocity on the Upstream Migration Behavior of Grass Carp in the Reaches of Spur Dikes

Abstract

The construction of spur dikes alters the flow pattern of rivers and affects the upstream migration behavior of fishes. Traditional rock-fill spur dikes and experimental permeable spur dikes with a “Weighted Excess Storage” (WES) profile were evaluated using hydrodynamic experiments and experiments on the upstream migration behavior of juvenile Grass Carp (Mylopharyngodon idella). The swimming ability and upstream migration paths of juvenile Grass Carp in the spur dike were analyzed, and the relationship between the upstream migration success rate of Grass Carp and the diversity of flow velocity was studied. The induced velocity and critical velocity of juvenile Grass Carp with a body length of 5 ± 0.5 cm are 0.1 m/s and 0.7 m/s according to the experiment. The flow velocity diversity index increased roughly in a power function trend with the increase in flow discharge, and under the same flow conditions, the flow velocity diversity index of permeable spur dikes was greater than that of rock-fill spur dikes. When the flow velocity was within the preferred velocity range of Grass Carp, the success rate of upstream migration increased linearly with the diversity of flow velocity. When the velocity was greater than 60% of the critical velocity of Grass Carp, the success rate of upstream migration dropped sharply. Compared with rock-fill spur dikes, the experimental permeable spur dikes provide a passage for the upstream migration of fishes and reduce the impact on the upstream migration of fish. The results of this research provide theoretical support for ecologically optimized designs of spur dikes and the ecological management of rivers.