This thesis discussses the use of mathematical modeling of a turbulent flow using PCFLOW2D in a
fishway. Recently in Slovenia they gained increased attention for the research of the improval of the
longitudinal connectivity of watercourses to achieve good ecological status required by Water
Framework Directive for all existing and new fishways by the year of 2027. We can therefore use
hydraulic models to calculate different flow conditions of various fishway examples to assess their
suitability for fish migration. In the first part of the thesis we present the main features of the most
common types of fishways currently used in the world and list their strengths and weaknesses. We then
explain the importance of efficient fishways and how it could improve our understanding by collecting
large data of standardized measurements of migrations on existing fishways. In the second part of the
thesis we use the example of the vertical slot fishway used on HPP Arto Blanca. Its flow can be described
as an example of a two dimensional flow. where the vertical component of the velocity is negligible,
therefore we use depth-averged model of flow for the existing two planar velocity components. We
perform our calculations with the k-ε turbulence model on four different examples of longitudinal slopes
in five different flow conditions, which shows that the degree of turbulence is only slope dependent.
When checking the suitability for target fish species it turns out that only the lowest level of longitudinal
slope of 10 cm per pool gets sufficient enough low levels of dissipation of the turbulent kinetic energy.