DEBRIS FLOW RUN-OUT DISTRIBUTION MODELLING AT PASIR PANJANG VILLAGE, SALEEM DISTRICT, BREBES REGENCY, CENTRAL JAVA FOR HAZARD ASSESSMENT

• Main Author: Andra Dinata, Indra
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/44184
• Institution: Institut Teknologi Bandung

The occurrence of several landslides followed by the debris flow, such as Pasir Panjang Landslide on February 22, 2018 has made terrible destruction and 18 casualties. This landslide occurred in Pasir Panjang Village, Saleem District, Brebes Regency, Central Java with coordinates 108° 47' 19.68" E and 7° 7' 6.59" S. In general, debris flow geometry can be divided into source area, flow track and depositional area. The source area consists of vulcanic breccia from Kumbang Formation. The debris flow flows toward southeast in slopes that have angle 35°-45°. Soil cover in the landslide location is brown-grayish brown clay with 3-15 m thickness. Debris flow modeling is carried out to determine the distribution and distance from the source of landslide to the end of the flow. This debris flow study uses numerical simulation method with a graphical user interface (GUI). The method is based on the law of the equations of momentum, continuation, riverbed shearing stress, riverbed deformation and erosion/deposition. This debris flow modeling is helped by 2D Kanako software. Simulations in 1D use two layer models as a simple way to represent the phenomenon of particle sorting. This model uses the basic equation of debris flow mixed materials layer and considers vertical changes in sediment concentration. Simulations in 2D gradually calculate the vertical slope and stress that are distributed perpendicularly from the flow direction. These conditions cause the vertical exchange of particles will decrease. From the modeling of Pasir Panjang landslide case, the concentration value of 0.3 indicated the best fit simulation result. The flowing material of this landslide has very long distance, 2.3 km in approximate. It occurs because approximately 275 thousand m3 volume material flowing with 26 km/hour of maximum flow rate. There are two debris flow potentials in the east and west of the Pasir Panjang debris flow location. The debris flow potential in the east has 24 km/hour maximum speed, whereas the debris flow potential in the west has 25 km/hour maximum speed. Debris flow hazard levels can be grouped according to the flow thickness of the debris material into three levels, they are low hazard level (0-25 cm), medium hazard level (25-50 cm) and high hazard level (>50 cm).