DESIGN AND PRELIMINARY RESULTS OF DEBRIS FLOW ANALOG MODEL WITH LABORATORY SCALE, CASE STUDY BENTARSARI SUBWATERSHED Imam A. Sadisun (a, b*), Indra A. Dinata (a), and Lambok M. Hutasoit (a)
(a) Applied Geology Research Group, Faculty of Earth Sciences and Technology, Institut Teknologi Bandung, Indonesia
*sadisun[at]gmail.com
(b) Research Centre for Disaster Mitigation, Institut Teknologi Bandung, Indonesia
Abstract
Bentarsari Subwatershed is located at Brebes Regency administrative area, Central Java. This subwatershed is bounded by hills composed by volcanic breccia of Kumbang Formation (Tpk) and the bottom of the basin is dominated by sedimentary rocks. Volcanic breccias have a relatively old age and appear to have more intensive weathering process so they are more susceptible to landslides. The main materials for debris flow modeling are moderate to highly weathered volcanic breccia unit and completely weathered volcanic breccia to residual soil. The rainfall scenarios will used 50 mm/day (lowerbound of heavy rain class), 100 mm/day (lowerbound of very heavy rain class), and 150 mm/day (lowerbound of extreme rain).
Laboratory scale analog model design with software can already model the movement of solid materials. An actual laboratory scale analog model has been made with 1.75 m high, 2 m long, and 1 m wide dimensions. The simulation uses a spherical material with a density of 1.84 g/cm3. The density value is taken from average laboratory results of completely weathered volcanic breccia to residual soil because which dominated the debris flow events in Bentarsari Subwatershed. The simplification process is carried out on spherical material with 4 cm and 2 cm diameter to depict moving material. The volume of solid material used in the simulation is 0.07 m3 while the volume of liquid is 0.03 m3. When the analog model is tilted 50 degree, the slip plane which forms then expands to the rear of slope, the flowing material moving downwards, colliding with the previously deposited material, forming a flow which bends slightly to the left of slope.
Keywords: debris flow, analog model, deterministic modelling
