Erosion under the conveying pipeline affected by river flow at the cross to rivers is one the important reasons for breaking the pipelines that can lead to leakage. While the mechanism of erosion under the conveying pipeline in steady flow has been studied by many researchers, studies have shown the importance of scouring research in flood times under unsteady conditions. So, this study has been concerned with the investigation of bed river erosion under the conveying pipeline at the conflict of river in unsteady condition. To achieve this aim, some effective hydrograph’s parameters were changed in different scenarios and the results were compared to the steady condition. The result showed the erosion’s ratio of unsteady condition to steady one was 34 to 69 percent. Also, the rise of flood hydrograph’s peak led to increasing depth erosion from 7% to 22%.