SEDIMENT TRANSPORT STUDY IN GROUNDSILL SERIAL STRUCTURE IN BOGEM BRIDGE, OPAK RIVER, SPECIAL REGION OF YOGYAKARTA

• Main Author: Harset, Demetrio
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/76443
• Institution: Institut Teknologi Bandung

The groundsill structure that is located downstream of the Bogem Bridge failed in 2021. The failure was caused by a significant increase in discharge in the Opak River due to heavy rains. The damage to the structure resulted in soil erosion and subsidence of the riverbed around the foundation of the Bogem Bridge. Due to the dangers posed, the Balai Besar Wilayah Sungai Serayu Opak (BBWS-SO) rebuilt the groundsill structure of the Bogem Bridge. The study conducted in this research aims to examine the effectiveness of the groundsill that has been built and evaluate the performance of the groundsill structure for securing the Bogem Bridge by observing changes in the riverbed and the distribution of sediment transport. The hydrological approach was carried out using the HEC-HMS program with an initial topographical analysis using the Watershed Modeling System (WMS) program, and the hydraulic approach and sediment transport were carried out using the HEC-RAS 6.4.1 program. The sediment transport equation used in this study is to use the Engelund-Hansen, Ackers-White, and Yang equations. The river geometry used is the existing river geometry before the construction of the groundsills and the river geometry after normalization and installation of the upstream and downstream groundsills. The results of research conducted with 12 scenarios obtained the use of design discharges, namely Q2 and Q50 which are discharge used for planning groundsill buildings. Changes in the riverbed and sedimentation patterns under existing conditions in both the 2D and 1D simulations tended to be stable but at the end of the simulation, the erosion and sedimentation processes were seen to be getting higher, with the most significant erosion depth in the existing geometry using the Engelund-Hansen sediment transport equation are 11.25 m. The simulation results with normalized geometry and groundsill buildings show stable results. The condition of the riverbed around the bridge, between the upstream groundsill and the downstream groundsill, did not experience any change in the riverbed. The results of the 2D simulation show that sedimentation occurs at the upstream groundsill with the most significant height of 4.10 m. Then there was erosion downstream with a maximum depth of 0.90 m. Analysis using the sediment transport equation is considered to be a reasonably optimal analysis because it can reflect the original conditions in the field.