Analysis of Debris Flow Hazard in Volcanic Soil by the Flood Flows Modelling (DFLOWZ) and Nakayasu Synthetic Unit Hydrograph

The Mount Batur Geopark area is vulnerable to debris flow triggered by heavy rainfall and weathered rocks that threaten the villages below. The estimation of the potential debris flow inundated area in this study has been determined by using the DFLOWZ model. The Digital Elevation Model (DEM) is the primary requirement data input in the model. Furthermore, the analysis of mean rainfall intensity and the hydrograph flood design have been calculated by the polygon Theissen and Nakayasu synthetic unit hydrograph method, respectively. The observation result has exhibited that basin flow occurs in the valley and river at the elevation ± 1500 m above sea level, which curves in hilly valleys and westward flow direction. The DFLOWZ analysis result depicts the area potentially inundated by a debris flow event as 49,830 m2 with an inundation height based on the slope of 5-7 m. Furthermore, the peak of discharge debris flow, the debris flow volume, and the debris flow range are 100.15 m3/s, 50,072.85 m3, and 49.5 meters, respectively. This condition indicates that there is a risk of debris flow in the form of sand, silt, and boulders around the river in the range of 49.5 meters and a sediment thickness of 1-1.5 meters.