### State-of-the-Art Review
[36] on the experimental weir-type fishway showed that longitudinal turbulence intensity in the surface layer (in the main flow area) was larger than that in the lower, as well as the variation in Reynold's shear stress. Turbulence increased slightly with a 50% increase of the flow rate through the fishway. [PERSON] [37] has investigated the flow velocity field in pool-weir fishways with an orifice and notch using a physical model. He observed the highest turbulence between two main flow layers--over the notch and through the orifice. Normalized turbulent kinetic energy values were highest in the orifice jet zone and lowest in the recirculation zone (<25%). [PERSON] et al. [12] analyzed the performance of RANS k-\(\epsilon\) and LES-Smagorinsky turbulence models in a 3D numerical model of a vertical slot fishway using OpenFOAM. They compared the results with data acquired from a scaled laboratory model for two flow scenarios and found that the model accurately simulated the velocity spatial distribution, while it overestimated or underestimated the turbulent kinetic energy and Reynold's stress. [PERSON] et al. [38] came to a similar conclusion, comparing numerical results for flow in the pool-weir fishway obtained from OpenFOAM and FLOW-3D, and validated with in situ ADV measurements. Both models accurately predicted velocity magnitudes, while they significantly underpredicted turbulent kinetic energy levels. They found that models also could not reproduce the finer features of the flow, indicating that turbulence in the fishways might need to be validated using physical model data rather than focusing exclusively on numerical models [39]. Technical fishways are often considered for space-constricted locations or in regulated streams that are already channelized, e.g., in urban areas of Europe. Pool-weir fishways are the most hydraulically effective technical fishway [40], having advantages over other types of technical fishways in their operability over a wider range of flow conditions and a passage of broad fish species [26]. Consequently, they are the most utilized type of fishway, followed by pool-orifice, vertical slot, and Denil-type fishways [41]. They are most useful for small streams because they require the smallest flow rate of all the fishways (a smaller flow rate can be compensated with a lower headloss between the pools, thus resulting in more pools and a longer fishway). The main advantage of the pool-orifice fishway is the absence of energy carryover from one pool to another, where energy dissipation takes place in the pool's recirculation zone that serves as a fish resting area [42] with velocities, turbulence kinetic energy, and volumetric dissipated power lower than in a vertical slot fishway [43]. In the vertical slot fishway, pools are created using baffles that divide cross-walls, allowing fish passage at any depth and thus giving the possibility of migration for more diverse species. The advantage of vertical slot-type fishways is the capability of allowing the fish passage across the entire flow depth, thus being less sensitive to flow oscillations, while their disadvantage is their need for a high flow rate for the migration of larger fish [44]. The main difference between the pool-orifice and vertical slot fishways is the energy dissipation rate: in the pool-orifice fishway, the energy dissipation rate is linearly correlated to the increase in the flow rate, while in the vertical slot fishway, the energy dissipation rate increases with the fishway bottom slope under constant flow rate [45].