STUDY OF SEDIMENT CONTROL OF THE OPAK RIVER POST OF 2010 MERAPI MOUNTAIN ERUPTION IN SLEMAN DISTRICT

• Main Author: Hadiranti
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/72046
• Institution: Institut Teknologi Bandung

Mount Merapi is the active volcano in Indonesia, the eruption that occurred in 2010 was a major eruption with a return period of 100 years. Dominant debris flow to the Opak – Gendol River Basin. The biggest debris flood occurred in 2010 – 2011. One of the disaster mitigation on the Opak River is the sabo dam infrastructure, sabo dam acts as a sediment controller and can minimize the potential for debris flow. Currently, in the upper reaches of the Opak River, there are five sabo dams, in 2022 two additional sabo dams have been built, namely OP RRC4 and OP RRC3a. In this study, research will be carried out, namely the study of sediment control in the Opak River before and after the Sabo Dam OP RRC4 and OP RRC3a. The hydrological approach was carried out using the HEC-HMS program with initial topographic analysis using ArcGIS 10.3 software. The hydraulic approach was carried out using the HEC-RAS 6.3.1 2D non-Newtonian software and erosionsedimentation analysis using the Kanako 1.44 software. The occurrence of debris flooding on 3 January 2011 after the eruption of Mount Merapi was used as a calibration parameter for the results of hydrological, hydraulic, and erosionsedimentation analysis. The river geometry used is the river geometry measured in 2020. The results showed that the canal condition in the existing conditions before the existence of two new sabo dams using Q2 and Q100 discharge at the observation point occurred run off, after the existence of Sabo Dam OP RRC4 and OP RRC3a the channel did not occur run off. Based on the results of a comparison of scenarios using the Q2 and Q100 discharge, the decrease level of debris flow can be reduced by up to 44,83% using the Q2 discharge and the decrease level of debris flow can be reduced by up to 47,21% using the Q100 discharge. The results of the analysis of erosion and sedimentation using Q2 and Q100 discharge show sedimentation in all sections of the river in the study location, the analysis of erosion and sedimentation was carried out using the scenario of adding one sabo dam to become six sabo dams and two sabo dams to become seven sabo dams. The results of the analysis using the Q2 discharge obtained a reduction in sedimentation that occurred downstream after the Sabo Dam OP RRC3a location with six sabo dams of 1,794 m3 (6.37%) and the reduction that occurred downstream after the sabo dam OP RRC3a location with seven sabo dams of 5,822 m3 (20.67%) using Q2 discharge. The results of the analysis using the Q100 discharge obtained a reduction that occurred downstream after the Sabo Dam OP RRC3a location with six sabo dams of 1,200 m3 (1.2%) and the reduction that occurred downstream after the sabo dam OP RRC3a location with seven sabo dams of 4,357 m3 ( 4.36 %). The addition of the construction of the Sabo Dam OP RRC4 and OP RRC3a as a disaster mitigation for volcanic eruptions is quite effective in reducing the potential for debris flows. Construction of series sabo dam simultaneously is more effective in reducing sedimentation in the downstream.