# A Novel Suspended-Sediment Sampling Method: Depth-Integrated Grab (DIG)
## 3 Results
This discrepancy in measured Sandse between the two methods could be due to only measuring one vertical with the DIG method and measuring it at a location with potentially higher sand transport. The location of the DIG samples was at the centroid of the channel which is generally the deepest and fastest part of the river because it was the same location where transit rates were tested and determined. When comparing the Fines and Sands between EWDI and DIG sampling methods, the range of Sands was generally less than the Fines. The maximum measured Sands was 629 mg/L (DIG) while the maximum measured Fines was 1572 mg/L (DIG). There was a closer agreement between the EWDI-Fines and DIG-Fines than the EWDI-Sands and DIG-Sands (Figure 6). Most of the Fines data plotted near or on the 1:1 line (Figure 6). There was more variability around the 1:1 line for Sands data. The same sample that deviated the furthest from the 1:1 line in Figure 5 also plotted the furthest above the 1:1 line, with the DIG sample having an additional 351 mg/L of Sands than the EWDI sample. A paired Wilcoxon test, also known as the Wilcoxon signed-rank test, was used to compare samples collected by 2 different methods [30]. The paired test takes the sample differences from each collection method and tests the null hypothesis that the median difference is equal to zero. Distributions of paired samples are shown in Figure 7. The results from the paired Wilcoxon test are shown in Table 3.  
Figure 5: Relationship between depth-integrated grab (DIG) and equal-width or -discharge increment (EWDI) sampling methods using the suspended-sediment concentration (SSC) laboratory method. The black line is the 1:1 line. Statistically significant (\(p\)-value less than 0.05) differences were not found between EWDI and DIG methods for any sediment type (SSC, Sands, and Fines; Table 1). There was not a statistically significant difference between EWDI-Fines and Grab-TSS (Table 3). Conversely, there were statistically significant differences between all the other comparisons (EWDI-SSC-Sands and DIG-SSC-Fines) and Grab-TSS. The Grab-TSS samples were generally lower than EWDI and DIG methods. The median difference between EWDI-SSC and Grab-TSS was 28 mg/L, and the median difference between DIG-SSC and Grab-TSS was 15 mg/L (Table 3). For Fines, the median differences were 1.72 and 1.67 between EWDI-Fines and Grab-TSS, and DIG-Fines and Grab-TSS, respectively (Table 3). Figure 6: Relationship between Sands and Fines concentrations for equal-width or -discharge increment (EWDI) sampling method (x-axis) and depth-integrated grab (DIG) sampling method (y-axis). The black line is the 1:1 line. \begin{table}
\begin{tabular}{l l c c} \hline
**First Method** & **Second Method** & **Median** & \(p\)**-Value** \\ \hline EWDI-SSC & DIG-SSC & 0 & 0.68 \\ EWDI-SSC & Grab-TSS & 28 & \textless{}0.01 \\ DIG-SSC & Grab-TSS & 15 & \textless{}0.01 \\ EWDI-Sands & DIG-Sands & 0.09 & 0.96 \\ EWDI-Sands & Grab-TSS & \(-33\) & \textless{}0.01 \\ DIG-Sands & Grab-TSS & \(-47\) & \textless{}0.01 \\ EWDI-Fines & DIG-Fines & 0.65 & 0.42 \\ EWDI-Fines & Grab-TSS & 1.72 & 0.06 \\ DIG-Fines & Grab-TSS & 1.67 & \textless{}0.01 \\ \hline \end{tabular} Abbreviations: \(p\)-value, probability value; \(\varsigma\), less than; EWDI, equal-width or -discharge increment; SSC, suspended-sediment concentration; DIG, depth-integrated grab; TSS, total suspended solids.  
\end{table} 
Table 3: Results from the paired Wilcoxon test [30].