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The authors outline in this paper the basic principles which can be used as a guide for planning fish passage facilities at dams or obstructions. The first part addresses the negative effect of barriers across rivers on natural fish population, contributing to the reduction of abundance and even the extinction of species. French statutory legislation on fish passage at obstructions is given. Functional features and design parameters are described for different types of fish facilities, focusing on the advantages, the limits and the cost of each type: pool type fish passes, baffle fish passes, fish locks, fish elevators, natural bypass channels, pre-barrages. Stress is laid on the importance of the location of the fishway, hydraulic conditions and the flow discharge at the entrance. Special mention is made of fish facilities for shad, young eels and elvers. Various monitoring techniques to evaluate fish passage efficiency are presented (trapping, automatic counters, video recording, telemetry). Fish passage through culverts, rock weirs and at estuarine obstruction are addressed. Downstream migration problems at hydroelectric power plants are turbines, design of fish screening and alternative behavioural diversionary techniques used to prevent entry of downstream migrants s into intakes. Special mention is made of the most popular technology in France, i.e. surface downstream bypasses associated with conventional trashracks, focusing on their design criteria, advantages and limits.
