## 3 Results  
### Validation of Existing Models M1 and M2  
Given that the model proposed by [PERSON] [14] used various watershed characteristics as explanatory variables, the latter must be obtained based on GIS analysis, and the target watersheds must first be determined through watershed delineation. Tributaries of various sizes flow in the main stream of the Nakdong River, and in the case of the total sediment load used for validation, measurements were acquired at upstream and downstream of the confluence of the Geumho River (watershed area = 2053 km\({}^{2}\)), Hwang River (watershed area = 1340 km\({}^{2}\)), and Nam River (watershed area = 3644 km\({}^{2}\)) in the continuous main stream of the Nakdong River (Figure 1c). The SD values of gauging points located in the Geumho (Dongchon), Hwang (Jukgo), and Nam Rivers (Jeongam) used for the development of M1 and M2 models were 49.7, 57.2, and 33.7 tons/km\({}^{2}\)-year, respectively (Figure 6). Figure 5: Estimating procedures for total suspended load from measurement using LISST-100X. (**a**) Measured water velocity by ADCP, (**b**) two-dimensional (2D) distribution results from the measured SSC by LISST-100X, and (**c**) 2D distribution outcome based on the EDI method used for the estimation of total suspended sediment load. Figure 7 shows the comparative results among different measurement points, which indicate big differences between upstream and downstream after tributary merging of Hwang River and Nam River. Figure 6: Measurement locations of validation data near the (**a**,**b**) Geumho, (**c**,**d**) Hwang, and (**e**,**f**) Nam River confluences. In case of the Geumho River, the confluence was very complex (Figure 6b). Given that most of the inflow sediments were deposited downstream of the confluence, only the watershed after the confluence (W1) was considered. Taking into account the measurement results, the watersheds set for validation of M1 and M2 include those at upstream and downstream locations those of the Hwang River confluence (W2 and W3) and those of the Nam River merging (W4 and W5). Table 9 lists the explanatory variables and predicted SD values for the five watersheds for model validation. Considering the range of SD values of 44, 6, 21, 56, and 102 tons/km2-year at the five gauging points located in the main stream of the Nakdong River (N4, N6, N3, N5, and N7 in Figure 1c) used for calibration for model development, the predicted SD values were judged to be appropriate [14]. However, considering that the SD values of Waegwan (N7) and Jindong (N12) adjacent to the measurement points were 56 and 102 tons/km2-year, the results predicted by M1 and M2 did not show a considerable difference between Geum, Hwang, and Nam River, respectively. In addition, the models could not predict the different total sediment load between upstream and downstream of confluences. This is because the two models (M1 and M2) were developed to compare sediment yields between different watersheds. To be specific, many characteristics for watershed including tributaries did not change much when the change in the watershed area was small due to the tributaries or location of gauging points. According to previous studies, [PERSON] and [PERSON] [24] reported that SEMEP was capable of yielding reasonable and accurate estimations of the total sediment load. [PERSON] [14] also argued that M2 developed through the total sediment load predicted using SEMEP presented superior results compared with M1. However, the results of M1 developed using the MEP results are considered to show better predictability. The reason for the