Numerical simulation and redesign of Kamar Kajang Levee against Mount Semeru lahar flood based on HEC-RAS 2D non-newtonian flow model

Abstract

Mount Semeru is one of the most active volcanoes in Indonesia where the pyroclastic, debris, and mudflows from its activities have severely damaged its surrounding areas. On December 4, 2021, Mount Semeru erupted, followed by intense rainfall, and damaged the Kamar Kajang Levee after a lahar flood event. The collapsed Levee was located along the Leprak Lumajang River, one of the natural drainage systems for Mount Semeru. The dyke failure had led to severe economic loss. Thus, reconstruction of the training dyke is highly important. In response, this research aims to propose an improvement to the Kamar Kajang Levee. This study was done through field observation, numerical simulation, and levee design calculation. The Non-Newtonian algorithm in HEC-RAS 6.2 was employed to model the flood events. The 2D model has been verified using a Sentinel-2 image and has shown a 90.7% similarity of inundated area after flooded by at least 214 m3/s of flood discharge, equivalent to a 5-year design discharge. The engineering design analysis shows that an additional 3.5 m height is needed to anticipate future floods and mitigate events effectively.