SIMULASI BANJIR LAHAR DINGIN MENGGUNAKAN "SIMLAR" DI DAS KALI PUTIH, MERAPI

Cold lava floods in the watershed around the volcano are a threat from secondary disasters, including the watershed upstream of Mount Merapi. In 2010 the eruption of Mount Merapi spewed volcanic material of more than 140,000,000 m³. The area affected by the cold lava flood is the Kali Putih watershed area, one of the causes is that the upstream part of Putih River, Magelang Regency is covered with volcanic material of Mount Merapi as much as ± 9.3000.000 m³. As a result, cold lava floods hit residential areas on the banks of Putih River, and even parts of a Yogyakarta-Magelang Street was also covered by cold lava floods. Based on a similar incident, the experts created special software to simulate cold lava floods. SIMLAR 2.1 is an example of software to simulate cold lava floods in this study. The method combines input materials such as: hydrology, river morphology, sedimentation, and topography. In addition, the effectiveness of the sabo dam building will be studied by comparing the simulation results of SIMLAR 2.1 between whitout the sabo dam and the with sabo dam. As a result, the sabo dam building was able to slow down the rate of cold lava flood lunge because based on simulations with the sabo dam, points 12 (Sabo dam PU-C8 Ngaglik) and 13 (Sabo dam PUC2 Gempal) both minutes 240, 360, 600, or 780 the flood had not yet reached that point. While the simulation without the sabo dam, the flood has reached a point of 12 minutes to 360, 600, and 780 and point 13 in the 600 and 780 minutes. Besides, it functions as a barrier to soil erosion and then turns it into a sedimentation pile of 3.95 m at the first sabo dam (PU D1 Mranggen) minutes to 360