Analysis of Lahar Flood Hazard in Telaga Waja River, Karangasem Regency, Bali, Indonesia

The slopes of Agung Volcano starting from a radius of 4-5 km have already taken the form of many residential areas and agricultural land, so the possibility of an eruption will damage the area. Based on field observations, agricultural crops experience drought and their production is disrupted due to eruption on 27 November 2017. This study aims to create a model of lahar flood using Remote Sensing, Geographic Information System (GIS) and Laharz software. The results are physical characteristics, cross-sectional measurements and river meanders of Telaga Waja River as the lahar channel and the results of model of lahar floods. The width of the cross section varies between 50 meters to 200 meters with a depth of between 4 and 8 meters. At the upstream part, starting from samples 1 to sample 6, the cross-sectional condition of the river tends to be lower eastward,. This raises concerns that overflowing lahar floods can occur on the east sides of the Telaga Waja River. Meander measured in the field has a percentage of 12% to 29.5%. Sample 2, sample 4 and sample 5 had a high percentage of meanders, namely 29.47%, 26.70% and 25.84% which made these three points to be more prone areas with lahar flood. Greater lahar flood are found in the middle and downstream of the Telaga Waja River. The overflow condition is affected by the cross section and the condition of the river meander. Based on the modelling using aharz software and lahar volume scenarios of 1 million m³ (1^st scenario), 5 million m³ (2^nd scenario) and 10 million m³ (3^rd scenario), the total area that effected by lahar flood are 162.6 Ha for 1^st scenario, 376.63 ha for 2^nd scenario and 403.23 ha for 3^rd scenario.