Local scour assessment of Maos’ railway bridge in Serayu River based on the mathematical model HEC-RAS

Abstract The Maos Railway Bridge over the Serayu River, located in Maos Village, Cilacap Regency, Central Java, is a strategic infrastructure asset along the southern railway corridor of Java Island, operating since 1894. As part of the Trans-Java railway network constructed by the Staats Spoorwegen (SS), the bridge connects the main Yogyakarta–Cilacap railway line and plays a vital role in regional logistics distribution and passenger mobility. However, this 130-year-old structure is currently threatened by local scouring around its piers, which poses a significant risk of structural failure. This study aims to identify the potential scouring risks, analyze the influence of river flow on the morphology and depth of scour holes, and propose effective mitigation strategies. The methodology involves hydrological analysis, hydraulic modelling using HEC-RAS, and a comprehensive risk assessment encompassing physical impacts of a potential bridge collapse. Simulation results indicate that scour depths may reach up to -9.01 meters in piers and -17.95 in abutments. The bridge’s location on a river bend further intensifies scour due to secondary currents and velocity redistribution, highlighting the need for effective scour protection measures to ensure structural stability under extreme flow events.