## 4 Conclusions  
A hydraulic analysis method that can indirectly evaluate the attraction efficiency and passage efficiency of fishways was proposed in this study. For attraction efficiency analysis, a River-2D model with a fish physical habitat module was used, and the weighted usable area was suggested as an indicator of efficiency. For passage efficiency analysis, a 3D model with a free surface that can analyze the fluid behaviors of hydraulic structures was used. Moreover, the fishway efficiency was estimated with an ice-harbor fishway installed at Dalseong weir in the Nakdong River. In conclusion, although it was difficult to quantitatively replace the hydraulic analysis results with fishway efficiency, the efficiency was useful for identifying the overall tendency.  
The 3D analysis results showed that the flow velocity field inside the fishway showed a similar plunging flow in each pool, but various flow patterns appeared locally. To evaluate and improve the fishway passage efficiency, the average hydraulic values (e.g., average  
Figure 11: Results of ice-harbor type fishway at Dalseong weir: (**a**) Side view of flow structure in pools (2 rd, 3 th, 4 th); (**b**) Side view of flow structure in pools (15 th, 16 th,17 th); (**c**) Side view of flow structure in pools (32 th, 33 th, 17 th).  
flow velocity, water depth) as well as the results of elaborate modeling should be used. The results of River-2D analysis showed that the fishway located near the right bank was now not appropriate for attracting the target fish to the fishway due to the depth. A possible method to improve the attraction efficiency of the fishway is to move it to the left bank that has a lower depth. The attraction and passage efficiencies certainly require verification through direct fish monitoring in the fishway. However, when planning for a fishway or in difficult fish monitoring circumstances, hydraulic analysis, such as the method used in this study, has the advantage of indirectly evaluating the fishway efficiency.  
Although it is possible to roughly confirm the efficiency of fishway through hydraulic analysis, it is difficult to ascertain variations of the fishway efficiency caused by riverbed change. There is a limit to knowing how the riverbed will change. In future work, design and management plans for fishway reflecting riverbed change are needed.  
Conceptualization, [PERSON]-[PERSON] and [PERSON]-[PERSON]; methodology, [PERSON]-[PERSON] and [PERSON]-[PERSON]; software, [PERSON]-[PERSON] and [PERSON]-[PERSON]; Validation, [PERSON]-[PERSON] and [PERSON]-[PERSON]; formal analysis, [PERSON]-[PERSON] and [PERSON]; investigation, [PERSON]-[PERSON] and [PERSON] and [PERSON]-[PERSON]; writing-original draft preparation, [PERSON] and [PERSON] and [PERSON]; writing-review and editing, [PERSON] and [PERSON]; visualization, [PERSON] and [PERSON]; supervision, [PERSON] and [PERSON]; project administration, [PERSON] and [PERSON]. All authors have read and agreed to the published version of the manuscript.  
This research was funded by [National Research Foundation of Korea] grant number [NRF-2020R1F1A1076887].  
Not applicable.  
This study was carried out with a research grant from the National Research Foundation of Korea (NRF-2020R1F1A1076887).  
The authors declare no conflict of interest.