## 3 Results
### Turbidity vs. Sediment Concentration  
The water quality results obtained from five independently conducted experiments for each suspended-sediment particle size are depicted in Figure 2. Notably, the red clay sieved with a 200 mesh appeared to include impurities that affected the electrical conductivity, and the alkalinity of the mixture increased slightly with increasing concentrations due to lime or magnesium oxide present in the red clay (Figure 2a,c). The obtained values of the water quality factors did not differ significantly, indicating that the experimental conditions remained constant. This implied that the other factors affecting the relationship between water color, turbidity, and suspended concentration were well controlled. In the five experiments, 1044, 595, 520, 419, and 318 measurement results were obtained in total. The measurement results obtained during the addition of the suspended sediments presented a transmission value of less than 0.1; therefore, these 968 data points were considered nonreliable and were excluded from the analysis (Figure 3). Additionally, 489 data points (0.1 \(<\) transmission value \(<\) 0.3) that required caution were compared with the results used in the analysis and were considered as validation data because the concentration increased consistently after the addition of 100 g of red clay. In coastal waters, a significant proportion of particles exist as flocs or aggregates, which are clusters of several particles connected together to form a single entity through the tidal effect [28]. When the mixer was in operation, the measured sediment concentration was found to be more than twice as high compared to the measurements taken when the mixer was turned off and the fluctuation was maintained. This observation strongly indicates that flow conditions, such as tidal patterns, waves, and mixing processes in coastal areas and estuaries, have a substantial influence on concentration measurements. Consequently, the continuous monitoring and collection of measurement data are essential in coastal regions to account for these dynamic factors. To identify the effect of the particle size of red clay and the inclusion of substances other than red clay on the suspended-sediment concentration, the particle size distribution of the suspended sediment recorded using the LISST-200X every second was compared with that of the red-clay-only specimen recorded using the BW-tube method (Figure 4). Figure 3: Measurement results of (**a**) concentration and (**b**) turbidity in the 325 mesh experiment. Figure 2: Measurement results for the (**a**) electronic conductivity, (**b**) salinity, and (**c**) acidity (pH). The particle size distribution results obtained with the BW method (red line) significantly differed from the measurement results (dotted line) that were excluded from the analysis owing to data reliability issues or measurements during the red clay addition. We confirmed that the smaller the particle size, the greater the proportion of data to be excluded from the analysis. Furthermore, the analysis of the excluded data revealed that the reliability of the results obtained from the LISST-200x device was unsatisfactory. The particle size distribution curves derived from these measurements indicated that the instrument consistently underestimated the presence of particles, which is consistent with findings from other studies [29]. However, the two other methods employed in this study did not exhibit such a significant discrepancy and yielded acceptable results. In addition, sieving red clay with a 700 or smaller mesh was found to not produce a difference in the particle size. Red clay in units of 100 g was added nine times with the 200 mesh, three times with the 325 mesh, and two times in the remaining cases until the transmission value became 0.3 or less. The turbidity-concentration relationships derived from the experimental results were found to significantly differ for different particle sizes (Figure 5).