In submitting conference proceedings to Engineering Proceedings, the Volume Editors of the proceedings would like to certify to the publisher that all papers published in this volume have been subjected to peer review by the designated expert referees and were administered by the Volume Editors strictly following the policies announced on the conference website

The 9th Mechanical Engineering, Science and Technology International Conference (MEST 2025), organized by the Department of Mechanical Engineering, Universitas Muhammadiyah Kalimantan Timur, was successfully conducted on 11–12 December 2025 in Samarinda, Indonesia

This study analyzes the scouring characteristics of the Mahakam River section to support bridge design and safety assessments. Using a 100-year return period, the design rainfall was determined to be 1246 mm via the Log Pearson III method, resulting in a peak design flood discharge (Q₁₀₀) of 77,984 m³/s. Hydraulic analysis using a rating curve indicates a flood water level elevation of 32.578 m from the riverbed. Scouring calculations, including construction and stream scouring, were performed using Laursen’s and empirical methods. The results show a total scouring depth of 4.8 cm/year, primarily driven by stream scouring, as construction scouring was zero under current existing conditions. These findings emphasize the necessity of bank protection, such as gabions, to mitigate erosion risks for future infrastructure.