# Safety Assessment of Gas Pipelines Crossing River through Hydrodynamic Analysis
## 1 Introduction  
Gas pipelines supplying essential gas for daily life are regulated to ensure proper installation, maintenance, and safety management measures, thereby ensuring the safety of citizens. Typically, gas pipelines are buried underground or installed on bridges. However, when a gas pipeline must cross a river, burying it in the riverbed becomes a last resort. In such cases, it is essential to maintain and manage the burial depth to prevent the pipeline from being affected by changes in the riverbed. Hydrotechnical hazard categories [1] help in understanding the different ways that natural or human-induced changes in watercourses can impact pipelines. According to these categories, pipelines at water crossings can be affected by three primary types of channel movement: vertical channel movement, horizontal channel movement, and channel path movement. Firstly, vertical channel movement involves changes in the riverbed elevation, which can significantly impact the stability of buried pipelines. This category includes scour depth, referring to the removal of sediment around the pipeline due to flowing water, potentially leading to the pipeline becoming exposed and damaged. It also includes degradation and aggradation; degradation is the process whereby the riverbed lowers due to scour, while aggradation is the raising of the riverbed due to sediment deposition. Both processes can affect the depth at which a pipeline is buried and its subsequent stability. Secondly, horizontal channel movement refers to the lateral shifting of the river channel, which can affect the banks and potentially the pipelines buried near them. This category includes bank scour, which occurs when riverbanks erode, leading to the exposure and destabilization ofpipelines installed near the banks. It also includes encroachment, which happens when the river channel expands horizontally, encroaching onto adjacent land and potentially affecting infrastructure, including pipelines. Lastly, channel path movement describes the overall changes in the river's course, posing significant risks to buried pipelines. This category includes avulsion, a rapid change in the river's course, which can expose or even displace existing pipelines. It also includes meander cutoffs, which occur when the river creates a new, shorter path by cutting off a meander, leaving pipelines in the abandoned path exposed and unprotected. Operational pipelines are exposed to various risks, including performance problems, corrosion, and serious damages resulting from hydraulic, geotechnical, or seismic hazards [2]. Excessive hydrodynamic forces can cause leakage at the bottom of the river, thereby accelerating corrosion in humid environments. High flow velocities and turbulent currents increase stress on the pipeline surface, potentially leading to cracks or fractures that facilitate corrosion processes. This is especially critical in areas where water and sediment interact closely with the pipeline material, increasing the likelihood of long-term degradation. Given the potential accidents from floods, earthquakes, and disruptions of gas pipelines due to river maintenance, the installation of river-crossing pipelines involves assessing foreseeable accident probabilities and damage impacts, followed by implementing risk mitigation measures [3]. The EU and countries such as the United States, Canada, and Russia have established gas pipeline-related databases and are making efforts to collect and analyze accident cases of buried pipelines to enhance safety management and accident prevention [4; 5; 6; 7; 8; 9; 10]. The operation of technological systems must be reliable in terms of functionality and safety [11; 12]. The demands for safety are continuously increasing [13; 14; 15; 16; 17], and gas network operators should be concerned about accurate safety assessments whenever possible [18; 19]. The safety of river-crossing pipelines is increasingly threatened, especially due to natural phenomena such as floods and scour.