## 3 Results
### Flood-Road Network Information Coupling  
To facilitate the swift, organized, and safe evacuation of downstream residents, the first step is to identify the affected areas. This involves overlaying the results of the dam breach flood evolution simulation with downstream imagery data, elevation information, and road network details. The affected areas are then delineated by village. These include the Shanmei Reservoir Management Office in Quanzhou, Yanjiang Cement Company, Sanluo Village, Wancheng Paper Industry, Shinan Village, Jun Village, Xiawei Village, and Shikou Village, totaling eight affected units. Based on the latest government statistical reports and local village committee registration data, the estimated number of people at risk is 6091. The population affected by the flood, the estimated arrival time of the flood front, and the available time for safe evacuation for each affected unit are presented in Table 2.  
The selection of relocation sites was comprehensively evaluated based on elevation and road network data around the affected areas, considering two key factors: terrain flatness and proximity to roads. The downstream area of the Shanmei Reservoir is situated in a remote suburban region with limited economic development and few large-scale facilities. Given the sudden and destructive nature of a dam breach flood, an alternative relocation strategy was adopted to move the affected population. The selection of relocation sites took into account factors such as disaster risk, site scale, and emergency support conditions. By integrating remote sensing imagery, population data, and road network information from the downstream area of the Shanmei Reservoir, a GIS spatial analysis approach was employed to identify suitable emergency evacuation and relocation sites. This ensured the safety, accessibility, and spatial suitability of the relocation points. A total of eight affected points and five relocation points were designated, as shown in Figure 7. The affected points--corresponding to the Shanmei Reservoir Management Office, Yanjiang Cement \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Affected Unit Name** & \begin{tabular}{c} **Affected** \\ **Population (People)** \\ \end{tabular} & \
\begin{tabular}{c} **Flood Arrival** \\ **Time (min)** \\ \end{tabular} &
\begin{tabular}{c} **Available Time for** \\ **Safe Evacuation (s)** \\ \end{tabular} \\ \hline Shanmei Reservoir Management Office & 124 & 21 & 1260 \\ Nan’an Yanjiang Cement Co., Ltd. & 261 & 43 & 2580 \\ Nan’an Yanjiang Cement Co., Ltd. & 197 & 20 & 1200 \\ Nan’an Wancheng Paper Industry & 207 & 22 & 1320 \\ Co., Ltd. & 717 & 21 & 1260 \\ Shinan Village & 1093 & 37 & 2220 \\ Xiawei Village & 1475 & 25 & 1500 \\ Shikou Village & 2017 & 26 & 1560 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Information on each affected unit and the time available for safe evacuation. Figure 6: Line chart of inundation depth and flow velocity data of each monitoring point. (**a**) Flood depth line chart; (**b**) flood flow velocity line chart. The post-processed flood progression simulation results can be converted into flood evolution data with coordinates, which are then integrated with the road network model. Information such as affected points and relocation sites is incorporated into the model. For affected and relocation points not directly connected within the road network's topology, the shortest straight-line segments are used to link them to the road network. This forms the coupled flood-transportation model for the downstream area of the Shanmei Reservoir. Based on this model, the flooding and failure processes of the downstream road network are analyzed. Ten minutes after the dam breach, the downstream road network remains largely unaffected by the flood. At 20 min post-breach, the 192 Township Road Bridge, located at the U-shaped curve of the river, becomes submerged. At 30 min, the Shixia Bridge, Gangzai Bridge, and Boersi Bridge, near the river's T-junction, are also submerged.