PREDICTION OF DEBRIS FLOW IN BUKIT BERITI BESAR WITH LANDSLIDE AND RIVERBED EROSION AS INITIAL MECHANISMS AND ITS MITIGATION USING SABO DAM

DELLA ANGGUN LESTARI, Prof. Ir. T. Faisal Fathani, S.T., M.T., Ph.D., PIU., ASEAN.Eng.;Dr. Eng. Fikri Faris, S.T., M.Eng.

2021 | Tesis | MAGISTER TEKNIK SIPIL

A high potential area for landslide was identified upstream of the Air Beras River on Bukit Beriti Besar which was feared to generated debris flow through the Air Beras River. To protect geothermal assets in Cluster C which is located downstream of the Air Beras River, the simulation of debris flow initiated by landslide and riverbed erosion is necessary to be carried out and the protection work needs to be planned. This study aimed to conduct hydrological analysis, simulation of landslide and riverbed, simulation of debris flow, and plan protection work against debris flow using sabo dam. Frequency analysis obtained R24 for a 100-year return period of 126.3 mm, then with the Three-Point Hydrograph, the design discharge was 120 m3/s. Landslide analysis using Slope/W and Plaxis was intended to determine the source area boundary, thereby the volume of solid material was around 290,000 m3. The result of erosion analysis in riverbed using RAMMS showed that the maximum erosion occurred in the transported area with a maximum depth of 2 m. Based on the 3D simulation using RAMMS, it can be known that debris flow formed an alluvial fan with a flow height of about 5-10 m. The volume of sediment collected in the deposit area was 312,066.53 m3. Mitigation using the sabo dam was designed referring to SNI 2851:2015 and Technical Standards and Guidelines for Planning and Design of Sabo Structures (JICA, 2010), thereby in this case used two conduit sabo dams, each of which was equipped with a sub-sabo dam and an apron with a main sabo dam height of 10 m. This conduit sabo dam series was effective to control the destructive power of debris flow.

A high potential area for landslide was identified upstream of the Air Beras River on Bukit Beriti Besar which was feared to generated debris flow through the Air Beras River. To protect geothermal assets in Cluster C which is located downstream of the Air Beras River, the simulation of debris flow initiated by landslide and riverbed erosion is necessary to be carried out and the protection work needs to be planned. This study aimed to conduct hydrological analysis, simulation of landslide and riverbed, simulation of debris flow, and plan protection work against debris flow using sabo dam. Frequency analysis obtained R24 for a 100-year return period of 126.3 mm, then with the Three-Point Hydrograph, the design discharge was 120 m3/s. Landslide analysis using Slope/W and Plaxis was intended to determine the source area boundary, thereby the volume of solid material was around 290,000 m3. The result of erosion analysis in riverbed using RAMMS showed that the maximum erosion occurred in the transported area with a maximum depth of 2 m. Based on the 3D simulation using RAMMS, it can be known that debris flow formed an alluvial fan with a flow height of about 5-10 m. The volume of sediment collected in the deposit area was 312,066.53 m3. Mitigation using the sabo dam was designed referring to SNI 2851:2015 and Technical Standards and Guidelines for Planning and Design of Sabo Structures (JICA, 2010), thereby in this case used two conduit sabo dams, each of which was equipped with a sub-sabo dam and an apron with a main sabo dam height of 10 m. This conduit sabo dam series was effective to control the destructive power of debris flow.

Kata Kunci : discharge, hydrograph, deposit area, alluvial fan, RAMMS