# Safety Assessment of Gas Pipelines Crossing River through Hydrodynamic Analysis
## 5 Conclusions  
When burying gas pipelines under riverbeds in the Republic of Korea, installations should comply with the burial depth criteria specified by the Urban Gas Business Act. Various river maintenance projects, environmental factors, and flood events cause changes in riverbed elevation. Therefore, the periodic checking and management of burial depth are essential for sustainable safety. The analysis of riverbed variations using 1D and 2D models for a buried pipeline across a river indicates that both scouring and deposition occur. This conclusion was reached by utilizing previously measured data and analysis results. To practically examine riverbed changes, it is necessary to investigate the variations in the riverbed of the area where the pipeline is buried each year and compare these with the results of long-term riverbed changes. Due to recent climate anomalies and localized heavy rains, there is a trend of rainfall patterns differing from the planned flood patterns, which makes continuous measurement before and after the flood season necessary. This study systematized the methodology for checking the burial depth of river-crossing pipes using deposition estimation modeling in conjunction with hydrodynamic modeling. Through long-term and short-term deposition prediction targeting a narrow channel, it was shown that, despite the occurrence of scour and deposition, a burial depth of 1.2 m or more was maintained. To assess actual riverbed variations effectively, it is necessary \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Category** & **Drop Structure** & **River Crossing Structure** & **Sloping Drop Structure** \\ \hline Type & & & \\ Material & Reinforced concrete & Boulder stone, supporting pillar & Formwork, Boulder stone \\ Flow Type & Containment following reinforced concrete & Creating a gentle slope to maintain the flow & Filling stones along the interior slope of the formwork for riverbed protection \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Comparison of riverbed maintenance facilities. to investigate bed changes in the pipeline-buried area annually and compare them with the results of a long-term riverbed change analysis. Based on this, if the monitoring data and predictions show similar trends, it is necessary to continue monitoring for riverbed management rather than conducting additional analyses. If scouring traces are found during scouring investigations, or if there is a significant difference between the current and previously measured pipeline depths, it is essential to determine whether temporary local scouring occurred due to abnormal floods or whether riverbed changes have occurred due to upstream or downstream river works. Additionally, if continuous scouring occurs at the survey points, further hydraulic evaluations should be conducted, and calibrations should be performed based on the monitoring data. Moreover, short-term and long-term riverbed change re-predictions should be conducted, and reinforcement measures suitable for the field conditions should be implemented. In conclusion, the dynamic nature of river environments requires a comprehensive approach to determining burial depth criteria for gas pipelines. Integrating hydrodynamic safety assessments, periodic monitoring, and tailored reinforcement measures can ensure the safety and stability of buried gas pipelines. This approach acknowledges the complex and changing nature of river systems and the importance of adapting safety measures to specific regional conditions and ongoing environmental changes. By doing so, the safety and integrity of gas pipelines can be effectively maintained, minimizing the risk of exposure and damage due to riverbed change. The current hydrodynamic analysis methodology has played a significant role in evaluating long-term riverbed changes, but it has certain limitations. While one-dimensional models are useful for simulating long-term riverbed changes, they have limitations in fully capturing complex topographical changes and diverse flow conditions.