# Safety Assessment of Gas Pipelines Crossing River through Hydrodynamic Analysis
## 2 Materials and Methods
### Study Area Description  
The study area for implementing the hydrodynamic safety assessment is the Hyunpung Stream, a tributary of the Nakdong River located in Daegu Metropolitan City, South Korea. The upper reaches of the Hyunpung Stream consist of sand and gravel, while the lower reaches are composed of silty sand, and the middle and lower reaches have relatively gentle slopes. Urban gas pipelines are buried under the Hyunpung Third Bridge location, as shown in Figure 3. This location is situated in the downstream section of the river and has a gentle slope. Sediment can potentially influence the stability of river structures due to scour and reduce the flow passage area due to deposition. Moreover, when the sediment transport volume increases to a certain extent, sediment particles can cause friction and abrasion on the pipeline surface. This friction problem arises because suspended sediments collide with the pipeline, leading to material wear and potential damage over time. Increased friction can compromise the structural integrity of the pipeline and may accelerate corrosion processes, especially in areas with high sediment loads. Therefore, it is essential to consider  
Figure 3: The location of the study area and the gas pipeline (A–A). not only the effects of sediment on river structures and flow capacity but also the direct impact on the pipeline surface itself. Therefore, estimating sediment transport is crucial for ensuring watershed stability and pipeline safety. To this end, a series of field investigations have been conducted to classify the sediment size and determine flow discharge. According to previous studies [41] and river survey results by the Ministry of Land, Infrastructure, and Transport [42], the Hyunpung Stream is characterized by sedimentary features rich in sand and clay. The proportion of sand increases slightly downstream, particularly in comparison to gravel. For flow discharge, daily discharge data were used to generate the flow duration curve, and discharges representing durations of 95, 185, 275, and 355 days were extracted. Although various functions for estimating sediment transport exist [43; 44; 45; 46; 47], the Ackers and White function was adopted for the calculation based on the guidelines presented in the Comparative Evaluation of Some Selected Sediment Transport Formulas [41]. This formula explains how sediment is transported in flows such as rivers, considering variables like flow velocity, particle size, and particle concentration. The Ackers and White function is widely used in various river and hydraulic engineering applications for predicting sediment transport. It plays a significant role in research and design related to river stability, sediment transport, and pollutant transport. The function is a valuable tool for predicting sediment movement in complex river and hydraulic systems. It considers the hydraulic and sedimentological characteristics of sediment and is used to estimate sediment transport under various environmental conditions. It is an important tool in engineering and environmental projects. The Ackers and White function is a total load function developed from flume data for relatively uniform gradations ranging from sand to fine gravel. [PERSON] and White derived the equation using dimensional analysis and fitted coefficients to the equation based on experiments that included a range of bed configurations such as ripples, dunes, and plane bed conditions. This function does not have an intuitive shear stress, excess shear stress, or excess stream power formulation, unlike most other equations. However, it is built on a very similar excess mobility power function. The sediment flux is a function of a transport parameter.