## 4 Discussion  
### Effect of the Sediment Flux of the Hanjiang River on Erosion and Deposition in the Subaqueous Delta  
The deposition thickness of columnar sample ZZY07 in 1980-1989 was 0.38 m, and the average deposition rate was 4.22 cm/a; from 1989 to 2012, the deposition thickness was 0.31 m, and the average sedimentation rate was 1.36 cm/a; and from 2012 to 2016, the erosion thickness was 0.11 m, and the average sedimentation rate was \(-\)2.75 cm/a, but the chart bathymetric measurement error was \(\pm\)0.2 m, and the erosion and deposition amplitude at this location was less than 0.2 m, indicating that the water depth change at this location could be ignored. Therefore, ZZY07 was in an erosion and deposition equilibrium state during this period. ZZY07 was in a slightly depositional state from 1980 to 1989 and from 1989 to 2012, and was in a state of erosion and deposition balance from 2012 to 2016. From 1980 to 2016, a total of 0.69 m was deposited, and the average deposition rate was 1.92 cm/a. Although the channel outside Shantou Port showed a pattern of initial deposition followed by erosion during the period 1980-2016, at the local position of ZZY07, \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Column Number**} & **Grain Size Change** & \multicolumn{2}{c}{**Below the Boundary Depth**} & \multicolumn{2}{c}{**Above the Boundary Depth**} \\ \cline{2-5}  & **Boundary Position** & **Average Particle** & **Mean Value of Median Particle Size (\(\mu\)m)** & **Average Particle Size (\(\mu\)m)** & **Mean Value of Median Particle Size (\(\mu\)m)** \\ \hline ZZY51 & 0–42 & 20.7 & 10.0 & 33.2 & 12.5 \\ ZZY52 & 0–58 & 11.3 & 6.7 & 14.7 & 8.5 \\ ZZY55 & 0–54 & 19.1 & 9.9 & 26.4 & 12.3 \\ ZZY03 & 0–42 & 30.8 & 20.2 & 18.2 & 17.2 \\ ZZY07 & 0–96 & 23.5 & 20.2 & 9.5 & 9.1 \\ ZZY54 & 0–124 & 24.7 & 12.2 & 13.4 & 8.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Segmented particle size parameters of the columnar samples. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Column Number**} & **Sand** & **Silt Content** & **Clay** & **Average Particle Size Average (\(\mu\)m)** & **Median Particle Size Mean (\(\mu\)m)** & **Sorting Factor** & **Skewness** & **Kurtosis** \\ \hline ZZY51 & 2.8–22.6 & 55.5–72.8 & 16.8–36.8 & 25.0 & 10.9 & 2.0–3.9 & 1.7–4.3 & 2.4–23.3 \\ ZZY52 & 0.0–1.9 & 57.5–73.0 & 25.2–42.4 & 13.0 & 7.6 & 1.9–2.4 & 1.5–3.7 & 1.6–17.3 \\ ZZY55 & 2.9–19.0 & 60.7–72.7 & 19.0–30.2 & 22.3 & 10.9 & 1.9–2.9 & 1.7–5.1 & 2.7–33.7 \\ ZZY03 & 10.3–41.4 & 53.4–7.51 & 2.6–26.7 & 27.9 & 19.5 & 2.0–2.7 & \(-\)0.5–0.1 & 0.6–1.3 \\ ZZY07 & 9.0–49.6 & 45.9–82.2 & 4.4–33.7 & 16.9 & 15.0 & 1.4–2.9 & \(-\)0.3–0.4 & 0.7–1.2 \\ ZZY54 & 1.3–14.3 & 61.1–76.5 & 18.1–24.6 & 14.6 & 8.5 & 1.8–2.7 & 0.5–3.7 & \(-\)1.4–18.9 \\ ZZY04 & 2.2–43.9 & 53.3–76.6 & 2.8–30.5 & 18.7 & 13.6 & 1.8–2.5 & \(-\)0.5–0.2 & 0.6–1.4 \\ ZZY01 & 2.0–3.6-52.2 & 30.2–73.0 & 3.0–21.2 & 37.3 & 36 & 2.1–2.7 & \(-\)0.4–0.5 & 0.6–1.2 \\ ZZY05 & 4.4–50.1 & 43.9–82.7 & 5.3–26.7 & 19.5 & 19.9 & 1.2–2.3 & \(-\)0.3–0.5 & 0.7–1.4 \\ ZZY57 & 0.1–14.4 & 65.3–76.2 & 14.8–34.6 & 21.1 & 12.0 & 2.0–2.7 & 1.5–2.8 & 1.7–8.9 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Component content and particle size parameters of sediments in the columnar samples. the pattern changed from depositional during 1980-2012 to an erosion-deposition balance state during 2012-2016 (Table 2). The effect of river sediment fluxes into the sea on changes in erosion and deposition on underwater delta topography has similar manifestations in many regions. In the Mississippi River in the 1950s, for instance, the sediment flux into the sea decreased by approximately 50%, and the deposition volume of the underwater delta decreased from 317 \(\pm\) 54 Mt/a during 1874-1940 to 145 \(\pm\) 25 Mt/a during 1940-1979 and further decreased after 1979 to 87 \(\pm\) 15 Mt/a in 2005 [17].