## 5 Conclusions  
Motivation for the research presented in this paper was to quantify the hydraulic environment in the fishway types most commonly used on small barriers and analyze its dependency on the fishway geometry. Aim of this paper is to investigate the hydraulic environment of the three-dimensional flow and turbulence measured in the physical fishway model with the goal of providing information on the Reynold's shear stress distribution that would facilitate their design in accordance with bioccriteria boundaries defined by [PERSON] et al., disorientation and injury boundary. The main findings of the analyses are:  
1. RSS distribution across the 3 planes suggest that a streamwise RSS component is significantly larger than the horizontal and vertical component. In the PO fishway, \(\tau_{uw}\) is higher than concurrent \(\tau_{uw}\) and \(\tau_{vw}\) by 67% and 61% on average, respectively. In the VS fishway, \(\tau_{uw}\) is higher than concurrent \(\tau_{uw}\) and \(\tau_{vw}\) by 92% and 86% on average, respectively. Horizontal and vertical RSS components are similar, with average differences between them at 3% for all fishways and not exceeding 44% in the PO fishway and 14% in the VS fishway;2. A majority of all analyzed fishway configurations have been observed to have favorable conditions for fish passage, according to [PERSON] et al. 's bioccriteria boundaries. All PO fishways have RSS values below the injury boundary across the entire pool, while the disorientation boundary is exceeded only for orifices o10 and o12. For all VS fishways, the disorientation boundary is exceeded by a streamwise RSS component, while the injury boundary is exceeded for l60 and all slopes. \(\tau_{uv}\) and \(\tau_{vw}\) do not exceed the disorientation boundary, but are close to it (\(>\)20 N/m\({}^{2}\)) for all VS fishway configurations;
3. In the PO fishways RSS is inversely correlated with the orifice size and is correlated with its proximity to the main flow jet: all RSS components are observed to increase with the increase of the orifice size (while retaining the same bottom slope and pool length) and all RSS components are increasing from plane A towards plane C. A change in slope and pool length has no significant influence on the change in RSS values for PO fishways;
4. In the VS fishways, RSS is inversely correlated with the bottom slope: all RSS components are observed to increase with the decrease in the bottom slope. All RSS components are decreasing from plane A towards plane C. A change in the pool length has no significant influence on the change in RSS values for VS fishways;
5. A fraction of the RSS values below the bioccriteria boundaries is reducing with the increase in the orifice size for PO fishways and with the increase of pool length in the VS fishways. A fraction of RSS values below the bioccriteria boundaries in the VS fishway is significantly lower than in the counterpart PO fishway. Results obtained in this research suggest that for PO fishways, the critical design parameter is the orifice size, indicating that the smaller the orifice, the more favorable the flow conditions for the fish passage. With this in mind, special care needs to be taken when selecting the target fish species in order not to constrain their migration due to a small orifice size. For the VS fishway, the critical design parameter is shown to be the pool length, indicating that longer pools present more favorable flow conditions for the fish passage through the main flow jet, at the same time reducing the recirculation area due to the deflection of the jet into the resting area of the pool. Since the RSS values in the main flow jet are the lowest, the main flow jet should be in the focus of the optimal design of VS fishways. Conceptualization, G.G. ; methodology, G.G. and E.O. ; software, G.G. and R.F. ; formal analysis, G.G and R.F. ; investigation, G.G. and E.O. ; writing--original draft preparation, G.G. ; writing--review and editing, G.G., E.O. and R.F. ; visualization, R.F. ; funding acquisition, E.O.