The Influence of Rainfall Variation on Slope Stability: Case Study of Wanayasa Street Slope, Banjarnegara, Indonesia

This study aims to understand the rainfall characteristics in Karangkobar that potentially develop the rainfall threshold triggering a landslide in Banjarnegara-Karangkobar lane. To tackle the rainfall uncertainty, 11 years of rainfall data was employed to obtain three dominant rainfall models. The hydromechanical strength of soil was modeled numerically with the precipitation. Back analysis was presented to validate the model. The report provides the correlation of seepage flow and the safety factor of slope (FS) affected by the rainfall model. It resulted in a strong correlation between rainfall intensity to slope instability compared to rainfall duration. It is thus the slope failure mechanism identified as a debris flow rather than slope cracking. The slope result was relevant to understanding rainfall characteristics in Banjarnegara annually since 2014. The rainfall model proposed > 8 h rainfall duration and rainfall cumulative 45.6 mm or 5.7 mm/h intensity, as the rainfall threshold for the warning system in the study case area. This study report is applicable for the area where rainfall threshold is not available such as the Banjarnegara to Karangkobar route, which help the local citizens and policymakers decide on disaster management.