## 3 Applying Tools to the Fishway and Evaluating Efficiency
### Evaluation of Attraction Efficiency  
To evaluate the attraction efficiency of the ice-harp type fishway at Dalseong weir, a research area of approximately 1.5 km upstream and downstream of the target fishway was chosen. Furthermore, a finite element mesh was constructed based on the observed river topography data as shown in Figure 7. Fine meshes were constructed for detailed simulation of the fixed weir and fishway. The total number of nodes of the finite element mesh was 4245 and the total number of elements was 8405. Figure 6: Location of ice-harp type fishway at Dalseong Multifunctional weir. The low water season was selected because the spawning season of most fish inhabiting Korean rivers is spring (April to June); the usage rate of the fishway increases in this season as the upstream and downstream movements of fish increase and this period usually corresponds to the low water season. For upstream boundary conditions for model simulation, we used the Dalseong weir inflow, which is provided in real-time by Korea Water Resources Corporation. The inflow data for April to June (spawning season) were acquired each year between 2013 and 2017. The total number of inflow data were 455. Due to the large differences between maximum and minimum values of daily inflow, using the mode value among the 455 data, resulting in an inflow of 56 m\({}^{3}\)/s. Furthermore, the management level at the downstream end of the Dalseong weir was found to be always maintained at approximately 13.5 m assigned as the downstream boundary condition. Manning's roughness coefficient was set as 0.020 by referring to the Nakdong River Basic Planning Report [24] (Table 1). Furthermore, the simulation was performed without operating the movable weir as the weir was not operated when the inflow rate was 56 m\({}^{3}\)/s. Consequently, the water depth and flow velocity field in the low water season were obtained through the hydraulic module of River-2D, as shown in Figure 8a,b. The HSI information for the target fish species is required to calculate the WUA in the River-2D model. First, the dominant and subdominant fish species were acquired based on the fish monitoring data [25; 26; 27; 28; 29] at a point downstream of the Dalseong weir. Goby minnow was selected as the target species because it was the dominant species in general after the installation of the Dalseong weir and subdominant species from 2013 to 2017 (Table 2). Goby minnow is a fish sensitive to water quality, and it is necessary to improve the habitat in the same environment as the fishway [18]. In this study, the research result of [PERSON] et al. [15] was referenced for the HSI of the flow velocity and water depth for Goby minnow, as shown in Figure 2. The simulation result of the WUA for the target species based on the HSI using River-2D is shown in Figure 8c. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Section** & **Upstream Boundary Conditions:** & **Downstream Boundary Conditions: Water** & **Parameter: Roughness Coefficient** \\  & **Discharge (m\({}^{3}\)/s)** & **Surface Elevation (m)** & **Parameter: Roughness Coefficient** \\ \hline Dalseong weir & 56 & 13.5 & 0.020 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Simulation condition of River2D model. Figure 7: Bed contour and finite element mesh at Dalseong weirs. Figure 8: Cont. As shown in Figure 3, the preferred flow velocity for target fish (Goby minnow) is 0.05-0.25 m/s. In Figure 8b, the flow velocity was 0.30-0.35 m/s inside the fishway and 0.10-0.28 m/s near the fishway entrance. Thus, the preferred flow velocity was generated. Nevertheless, the WUA value, which is an indicator of attraction efficiency, was not large in the fishway entrance (Figure 8c) because of the effect of the water depth. While the preferred water depth of the target fish is 0.3-0.6 m (Figure 3), the water depth of the fishway entrance is more than 6 m (Figure 8a). Consequently, the ice-harbor fishway installed at the Dalseong weir is not effective for attracting the target species.