## 3 Results
### SOM Technique-Based Geomorphic Elements Mapping for Describing Subaqueous Bedforms  
The morphometric parameters calculated under a window size of \(7\times 7\) m when employing [PERSON]'s criteria were also combined into the input vector to train the SOM. When using the SOM technique, the number of output map units corresponds to the number of geomorphic elements, and the spatial arrangement form of the units can be one-, two-, or three-dimensional. Although the most reasonable number of map units is unknown, [PERSON] et al. [36] found that two and three dimensions offer a more meaningful classification. As a result, arrangement forms including (3 2), (4 2), (2 2 2), (3 3), and (5 2) were considered for arranging the output map units (Figure 4). The mean slope and cross-section curvature for each map unit were calculated as coordinates to plot the units within the feature space. According to a previous study [20], the units should be concentrated in three lines that correspond to three main groups (channel, planar, and ridge) to ensure that the units are well-defined as geometric elements. The units can then be sub-defined by slope (such as flat, gentle slope, moderate slope, steep slope, and very steep slope). Figure 3: Water depth profiles overlaid by [PERSON]’s criteria-based elements for (**a**) Cross-sections 1, 2, 4, and 5 under various slope tolerances, and for (**b**) Cross-sections 3 and 6 under various curvature tolerances. For Chizhou Reach, the suitable number of output map units was found to be 8, and the units were arranged in the form of (2 2 2), as shown in Figure 4a. Table 2 lists the suitable definitions and areas associated with each map unit. Map units 3 and 6 were given the same definition (moderate slopes, planar) because they host relatively smaller areas and are situated very close within the feature space. For the Yangtze Estuary, (5 2) was selected as the suitable arrangement of map units (Figure 4b), and map units 7 and 8 were given the same definition (moderate slopes, planar). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Method**} & \multicolumn{2}{c}{**The Sample Data of Chizhou Reach**} & \multicolumn{2}{c}{**The Sample Data of Yangtze Estuary**} \\ \cline{2-6}  & **(Map Unit)** & **Area (m\({}^{2}\))** & **Percentage** & **(Map Unit)** & **Area (m\({}^{2}\))** & **Percentage** \\  & **Element** & **(\%)** & **(\%)** & **Element** & **(\%)** \\ \hline \multirow{6}{*}{Wood’s criteria} & Plane & 36,586 & 32.05 & Plane & 35,455 & 29.54 \\  & Pit & 3668 & 3.21 & Pit & 4089 & 3.41 \\  & Valley & 30,124 & 26.39 & Valley & 29,972 & 24.97 \\  & Pass & 12,188 & 10.67 & Pass & 12,754 & 10.62 \\  & Ridge & 28,573 & 25.03 & Ridge & 33,267 & 27.71 \\  & Peak & 3029 & 2.65 & Peak & 4496 & 3.75 \\  & Total & 114,168 & 100.00 & Total & 120,033 & 100.00 \\ \hline \multirow{6}{*}{SOM technique} & (1) Flat, planar & 28,645 & 25.09 & (1) Flat, planar & 21,239 & 17.69 \\  & (2) Gentle slopes, channel & 16,624 & 14.56 & (2) Gentle slopes, ridge & 13,209 & 11.00 \\  & (3) Moderate slopes, planar & 8960 & 7.85 & (3) Moderate slopes, ridge & 14,528 & 12.10 \\  & (4) Moderate slopes, channel & 12,308 & 10.78 & (4) Steep slopes, ridge & 9517 & 7.93 \\  & (5) Gentle slopes, & 17,859 & 15.64 & (5) Very steep slopes, planar & 7255 & 6.04 \\  & ridge & & (6) Gentle slopes, channel & 12,141 & 10.11 \\  & (7) Steep slopes, ridge & 13,414 & 11.75 & (7) Moderate slopes, planar & 8927 & 7.44 \\  & (8) Steep slopes, channel & 13,126 & 11.50 & (8) Moderate slopes, planar & 11,827 & 9.85 \\  & & & (9) Steep slopes, channel & 11,310 & 9.42 \\  & & & (10) Very steep slopes, channel & 10,080 & 8.40 \\  & Total & 114,168 & 100.00 & Total & 120,033 & 100.00 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Statistical results for geometric elements under [PERSON]’s criteria, the SOM technique, and geomorphons.