The Prediction of Lahar Flood Event Impact on the Inundation Areas in Gendol River, Indonesia

One of the natural phenomena that inflict harm and fatalities is lahar flow. The Gendol River frequently experiences lahar flows from Mount Merapi, necessitating study. Predictions can be used to anticipate lahar flows and minimize casualties and material losses. The Nakayasu synthetic unit hydrograph is used in this study utilizing a simulation method based on the theory of Ashida, Takahashi, and Mizuyama, which modifies the hydrograph pattern and rainfall intensity values using the SIMLAR V2.1 application. Based on the simulation results, it was discovered that each simulated design had a different flow area, velocity, lahar volume, and flood height. Based on the result, it can be said that this study's hyetograph pattern significantly impacts how debris flows affect people. The more the hyetograph patterns, the higher the peak hydrograph value. Additionally, the increase in the hydrograph value is directly related to the increase in flow velocity. The rain intensity and pattern value also influence the number of areas affected by the lahar flow.