## 5 Hazard Assessment of Debris Flows in Niumiangou Valley  
The hazard assessment of debris flows in Niumiangou valley can be assessed using the following equation [35; 36]:  
\[H=0.29X_{1}+0.29X_{2}+0.14X_{3}+0.09X_{4}+0.06X_{5}+0.11X_{6}+0.03X_{7} \tag{13}\]  
Figure 5: The bend diagram of the Niumiangou valley \(8\cdot 14\) debris flow.  
In Equation (13), \(H\) is the hazard index of the debris flow (0-1 or 0-100%); \(X_{1}\), \(X_{2}\), \(X_{3}\), \(X_{4}\), \(X_{5}\), \(X_{6}\) and \(X_{7}\) are the transformed values (0-1) used to evaluate variables \(x_{1}\), \(x_{2}\), \(x_{3}\), \(x_{4}\), \(x_{5}\), \(x_{6}\) and \(x_{7}\), respectively, while \(x_{1}\), \(x_{2}\), \(x_{3}\), \(x_{4}\), \(x_{5}\), \(x_{6}\) and \(x_{7}\) represent, respectively, maximum depositional volumes of a debris flow (10\({}^{3}\)m\({}^{3}\)), frequency of debris flow occurrence scaled to the times per century (%), drainage basin area (km\({}^{2}\)), main channel length (km), drainage basin relief (km), drainage density (km/km\({}^{2}\)) and active main channel proportion (%).  
Transformation functions used for the evaluating variables can be seen in Table 3.  
The observed original data and transformed values of evaluating variables for debris flow in Niumiangou valley are shown in Tables 4 and 5, respectively.  
Based on Equation (13) and Table 5, the hazard evaluation result of the debris flow in Niumiangou valley \(H\) is equal to 0.82. According to the hazard degree classification standards of debris flow (Table 6), it can be seen that the hazard degree of the debris flow in Niumiangou valley is very high, belonging to a large-scale debris flow disaster. The evaluation result is compared with the debris flows occurring in 2008 and 2013 in Niumiangou valley post-Wenchuan earthquake. The hazard degree of the debris flow in Niumiangou valley is relatively higher than the other debris flows, which is consistent with the actual situation.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Exulating Factors** & \(\mathbf{X_{1}}\) & \(\mathbf{X_{2}}\) & \(\mathbf{X_{3}}\) & \(\mathbf{X_{4}}\) & \(\mathbf{X_{5}}\) & \(\mathbf{X_{6}}\) & \(\mathbf{X_{7}}\) \\ \hline Transformed values & 0.97 & 1.00 & 0.56 & 0.78 & 1.00 & 0.09 & 1.00 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Hazard degree classification standards of debris flow.  
\begin{table}
\begin{tabular}{c c c} \hline \hline
**Transformed Value (0–1)** & **Transformation Function** \\ \hline \hline \multirow{4}{*}{\(X_{1}\)} & \(X_{1}=0\) & for \(x_{1}\leq 1\) \\  & \(X_{1}=\log x_{1}/3\) & for \(1<x_{1}\leq 1000\) \\  & \(X_{1}=1\) & for \(x_{1}>1000\) \\  & \(X_{2}=0\) & for \(x_{2}\leq 1\) \\  & \(X_{2}=\log x_{2}/2\) & for \(1<x_{2}\leq 100\) \\  & \(X_{2}=1\) & for \(x_{2}>100\) \\  & \(X_{3}=0.2458\alpha_{3}^{0.3495}\) & for \(0\leq x_{3}\leq 50\) \\  & \(X_{3}=1\) & for \(x_{3}>50\) \\  & \(X_{4}=0.2903\alpha_{4}^{0.5372}\) & for \(0\leq x_{4}\leq 10\) \\  & \(X_{4}=1\) & for \(x_{4}>10\) \\  & \(X_{5}=2x_{5}/3\) & for \(0\leq x_{5}\leq 1.5\) \\  & \(X_{5}=1\) & for \(x_{5}>1.5\) \\  & \(X_{6}=0.05x_{6}\) & for \(0\leq x_{6}\leq 20\) \\  & \(X_{6}=1\) & for \(x_{6}>20\) \\  & \(X_{7}=x_{7}/60\) & for \(0\leq x_{7}\leq 60\) \\  & \(X_{7}=1\) & for \(x_{7}>60\) \\ \hline \hline \end{tabular}
\end{table}
Table 3: Transformation functions for evaluating variables [35; 36].  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Evaluating Factors** & \(\mathbf{x_{1}}\)/**10\({}^{3}\)m\({}^{3}\)** & \(\mathbf{x_{2}}\)/\%** & \(\mathbf{x_{3}}\)/**km\({}^{2}\)** & \(\mathbf{x_{4}}\)/**km** & \(\mathbf{x_{5}}\)/**km** & \(\mathbf{x_{6}}\)/**km/**km\({}^{2}\)** & \(\mathbf{x_{7}}\)/\%** \\ \hline Original data & 800 & 200 & 10.57 & 6.31 & 1.82 & 1.73 & 100 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Transformed values of evaluating variables of hazard assessment for debris flow in Niumiangou valley.