Special structures called fishways or fishpasses serve a purpose of allowing fish to pass through the step slope of a river formed as a result of artificial river damming by way of dams, weirs, steps and other structures or natural damming caused by waterfalls. There are three types of fishways: technical, natural and special. Prior to creating a design for a fishway, it is necessary to understand the hydraulic and hydrological conditions of the river and the technical characteristics of the water structure as well as to gather data on the existing species of fish, especially migratory fish, and the expected restitution. On the basis of these data, the design concept is prepared taking into consideration a number of determinants such as the size of the fishway, the location of the entrances and the water level, flow and velocity. The calculation procedure depends on the type and form of the fishway and the water flow conditions. For technical fishways (chamber, verical slot and Denila types), classical hydraulic formulae of outflow or overflow are generally applied. For natural fishways, the calculation process is more complicated. For example, in designing a stone slipway-type fishway it is necessary to determine the roughness coefficient, the medium and maximum velocities, as well as the maximum flow at a given water level. Besides, stream distributions, attracting currents, and sediment movement should be considered, which necessitates using mathematical models. The paper presents the procedures of hydraulic calculations for various fishway constructions.

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