## 5 Results  
### Monitoring of Bank Erosion Using Photogrammetry and LiDAR  
At Site 1, between November 2017 and February 2022, an erosion notch formed in the middle of the bank, mainly during the P2B period (February 2019-February 2020; Figure 4a). The sediment balances of the emerged surfaces of the bank were \(-\)418 m\({}^{3}\) for P1B, \(-\)447 m\({}^{3}\) for P2B, \(-\)345 m\({}^{3}\) for P3B, and \(-\)96 m\({}^{3}\) for P4B.  
At Site 2, the downstream half of the newly restored bank showed significant changes (Figure 4b). For the latter part, the first period P1C (September 2019-February 2020) recorded the most important bank retreat, with a maximum bank retreat of 28 m. This eroded area corresponded to an erosion volume of 6086 m\({}^{3}\) for emerged parts of the  
\begin{table}
\begin{tabular}{c c c c} \hline
**Survey Date** & **Method** & **Daily Mean Discharge (m\({}^{3}\)/s)** & **Water Surface Elevation (m)** \\ \hline
21 November 2017 & P & 13.9 & \\
12 February 2019 & L & 87.8 & 319.9 \\
7 February 2020 & L & 46.8 & 319.5 \\
8 April 2021 & L & 21.5 & 319.2 \\
3 February 2022 & L & 28.9 & 319.3 \\ \hline \end{tabular}
\end{table}
Table 4: Dates, daily mean discharges at the Vic-le-Comte gauging station (“[[https://hydro.eaufrance.fr](https://hydro.eaufrance.fr)]([https://hydro.eaufrance.fr](https://hydro.eaufrance.fr)) (accessed on 15 February 2023)”), and water surface elevations at the bank for all survey campaigns at Site 1, which permitted us to calculate the erosion rates of the restored bank. (P) Photogrammetry; (L) LiDAR.  
\begin{table}
\begin{tabular}{c c c} \hline
**Survey Date** & **Method** & **Daily Mean Discharge (m\({}^{3}\)/s)** & **Water Surface Elevation (m)** \\ \hline
7 February 2020 & L & 56.3 & 280.24 \\
8 April 2021 & L & 26.6 & 279.73 \\
4 February 2022 & L & 35.7 & 279.85 \\
7 October 2022 & L & 13.4 & 279.35 \\ \hline \end{tabular}
\end{table}
Table 5: Dates, daily mean discharges at the Limons gauging station (“[[https://hydro.eaufrance.fr](https://hydro.eaufrance.fr)]([https://hydro.eaufrance.fr](https://hydro.eaufrance.fr)) (accessed on 15 February 2023)”), and water surface elevations at the bank for all survey campaigns at Site 2, which permitted us to calculate erosion rates of the restored bank. (L) LiDAR.  
bank, and the estimated total eroded volume was 9647 m\({}^{3}\). During the second period P2C (February 2020-April 2021), the eroded area was mainly located on the downstream part of the active bank, with a maximum width retreat of 21 m and an eroded volume of 3149 m\({}^{3}\) for the emerged parts of the bank. The estimated total eroded volume for P2C was 6152 m\({}^{3}\).  
During the third (P3C; April 2021-February 2022) and fourth (P4C; February 2022-October 2022) periods, changes were minor (Figures 4 and 5). During the third period (P3C), 754 m\({}^{3}\) of sediments were eroded from the bank, preferentially located downstream from the apex of the bank, whereas the point bar gained 178 m\({}^{3}\) of sediment accretion. Erosion of the point bar was preferentially located at the bar head, and deposition occurred in the chute channel and on the bar tail near the main channel. During the fourth period (P4C), the erosion/deposition processes were insignificant, with a sediment balance of \(-\)78 m\({}^{3}\) on the bank and +48 m\({}^{3}\) on the point bar.  
Figure 4: (a) Bank retreat at Site 1. November 2017: 2 months after work; February 2019: 17 months after work; February 2020: 29 months after work; April 2021: 43 months after work; February 2022: 53 months after work. (b) Bank retreat at Site 2. September 2019: 0 months after work; February 2020: 5 months after work; April 2021: 19 months after work; February 2022: 29 months after work; October 2022: 37 months after work. The blue arrow indicates the flow direction.  
Figure 5: Altitudinal differences on the bank and the point bar at Site 2 for (a) the period P3C and (b) the period P4C. The blue arrow indicates the flow direction.