STUDY ON THE EFFECTIVENESS OF PELANGWOT SEDAYU-LAWAS FLOODWAY OPERATION PATTERN IN BENGAWAN SOLO WATERSHED

• Main Author: Nurhakim, Ardhi
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/80015
• Institution: Institut Teknologi Bandung

The changes in rainfall in Bengawan Solo Watershed have the potential to cause issues in the effectiveness of reducing discharge in the Pelangwot Sedayu-Lawas Floodway and changes in morphology of the Floodway channel. This research are conducted to analyze the impact of rainfall changes in the effectiveness of the Floodway operation pattern, occurring the changes in channel morphology and their handling. The research conducted involves hydraulic modeling, sediment transport, and sediment movement. The modeling is analyzed using HEC-RAS 6.4.1 under existing conditions and post management scenarios. In the hydraulic modelling, Q50 discharge and Q10 are used for the operation pattern of 5 and 3 gates due to existing scenarios, post-addition of thresholds and boulders, as well as post-normalization. Sediment transport studies are analyzed using daily discharge scenarios over a period of 2012-2022, and sediment movement studies are analyzed using the Hjulstorm Diagram. Based on the hydrological analysis, the 50 year return period flood discharge for the Bengawan Solo Watershed is 3963 m3/s. In the existing scenario with 5 gates, the Floodway provides a reduction of 980.02 m3/s with an effectiveness of 24.10%. While with 3 gates, the reduction is 769.25 m3/s with an effectiveness of 18.92%. In the alternative management scenario with 5 gates, the reduction ranges between 768.54 and 989.29 m3/s, and with 3 gates, in ranges between 619.34 and 769.25 m3/s. The sediment transport study from 2012 to 2022 indicates sediment aggradation of 141,808 m3 or approximately 14,180 m3/year. Meanwhile, the degradation amounts to 146,225 m3 or approximately 14,622 m3/year. The sediment movement analysis under existing conditions indicates that in the Floodway, degradation predominantly occurs in the upstream and middle section, while downstream sections experiences aggradation. Post the addition of boulders and thresholds, there are 4 changes in sediment transport from degradation to normal in the middle section, whereas in the normalization alternative, there are 11 changes in sediment transport throughout all sections of the Floodway.