## 3 Results
### Landslide Volume and Change in River Channel Volume  
The landslide volume and sediment budget of the Laishe River channel is shown in Tables 3 and 4, respectively. The location of the six sub-sections, upstream 3 (UP3), upstream 2 (UP2), upstream 1 (UP1), east village (EV), west village (WV), Yilin (YL), and Taiwan (TW) are denoted on Figure 1a. The abbreviation of the six sites is used afterward. Overall, the total landslide volume was approximately 36.16 million (M) m\({}^{3}\) from April 2009 to November 2015, and the landslide volume decreased from upstream to downstream (Table 3). Furthermore, the total landslide volume was \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Date**} & \multicolumn{2}{c}{**Control Point**} & \multicolumn{3}{c}{**Vertical Bias (m)**} \\ \cline{2-6}  & **Density (\(\text{pts}/\text{m}^{2}\))** & **Mean** & **SD** & **Maximum** & **Minimum** \\ \hline
10 April 2009 & 0.25 & 0.65 & 7.2 & 22.25 & \(-\)20.95 \\
28 August 2008 & 0.05 & 0.65 & 4.8 & 15.05 & \(-\)13.75 \\
23 January 2015 & 0.99 & 0.47 & 4.8 & 14.87 & \(-\)13.93 \\
6 November 2015 & 1.00 & \(-\)0.13 & 4.2 & 12.47 & \(-\)12.73 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Vertical bias between survey DEMs and LiDAR DEM. Figure 2: Distribution of ground control points (GCPs) of digital elevation models (DEMs). The dots denote the sampling point in this study and the colors denote various missions of the surveys. approximately 31.63 M m\({}^{3}\), which also shows a decrease from upstream to downstream. More than 80% of the landslide volume was produced from the upstream area. Moreover, the ratio of landslide volume in two periods ranged from 9.09% to 133.33%. Except for WV, all the ratios of landslide volume were over 77%, which means Typhoon Morakot dominated the landslide volume over a six-year period. Additionally, the \(>\)100% ratio in EV and YL may indicate that the recovery of landslide scars was measurable, for example, for vegetation recovery. However, the deposited volume was relatively lower than the landslide-induced erosion; only 0.49 M m\({}^{3}\) at EV and 0.06 M m\({}^{3}\) at YL. For the distribution of landslides (Figure 3a), four landslides with a hundred meter in length in UP3, two of which were old landslide areas (Mark 1 and 2) were used. Landslides continued to expand by subsequent typhoon-induced erosion, such as headward erosion (Mark 3). Additionally, hillslopes along the river channel were severely eroded due to river flow, causing lateral erosion-induced landslides from several meters to several tens of meters (Mark 4). The erosion pattern of UP2 was similar to UP1, a headward erosion and lateral erosion induced landslide (Mark 5-8). By combining the landslide material of UP3 and UP2 that accumulated with the river, UP2 had the largest sediment deposition in the catchment. Among the three landslides with a kilometer in length in UP1, two were caused by headward erosion (Mark 9) and one was in an old landslide area (Mark 10). The resulting lateral erosion led to the continuous expansion of the scale of landslides from 20-80 m (Mark 11). There were also many lateral erosions along the river channel. Two of these landslides were prominent, with lateral erosion mixed with headward erosion (Mark 12) and lateral erosion of the Neishe River (Mark 13). The landslides in WV were affected by two creeks (Mark 14). Although the creeks above the WV were not as severely eroded as the upstream area, they extended to the ridge and there was continuous collapse damage to the residential area. This was not as obvious, relatively, as the lateral erosion of the river channel in YL. The only factor that needed to be noted here was a potential debris flow (Mark 15) below the YL village. Typhoons Haitang and Talim in 2005, Kemi in 2006, Morakot in 2009, and Fanabee in 2010 were all followed by disasters.