Numerical Study on
Reducing debris flows
Impacts in Putih River,
Indonesia
Jazaul Ikhsan, Puji Harsanto, Tria Wulandari
Outline of Presentation
• Introduction
• Research Method
• Simulation Lahar (SIMLAR) V.1.1
• Discussion
Introduction
U
Mt. Merapi has erupted regularly and the eruption has been more active since 1992.
A huge sediment production threats people live and assets in the downstream area.
Merapi’s
Eruption in 2010
( SPOT satellite image ©CNES (2010), acquired by CRISP, NUS)
Merapi
City of Yogyakarta Runway of Yogyakarta
International Airport
Prambanan Temple (World Culture Heritage)
The 2010 eruption of Mt. Merapi is one of the biggest eruption, around 150 million m3.
Progo’s Tributaries: Pabelan, Putih, Blongkeng,
Research Method
• The objective of this study is to simulate impacts of debris flows and effects of sabo works to reduce the debris flow impacts.
• For simulation, the rain fall data was taken from Ngepos station. The hydrograph was generated using Nakayashu method.
Date 22 23 24 Time
13.00-14.00 11.5 66.5 0.0 14.00-15.00 2.0 24.5 12.5 15.00-16.00 2.5 1.5 0.5 16.00-17.00 0.0 0.5 0.0 17.00-18.00 0.5 0.5 3.6
Simulation Lahar (Simlar) V.1.0.
• Simulation Lahar (Simlar) software is
developed by Sabo Center and UGM, based on JICA –STC’s 2D Nu erical Si ulatio of
Riverbed Fluctuation and Deposition of Lahar.
• The software is modified on interface and
Governing Equation
• Momentum equation:
• Continuity equation:
Where, h is dept of flow, t is time, x and y are the coordinate along the longitudinal and transversal
direction, g is the gravity force, M and N are velocity in x and y direction, τby is turbulence stress.
Governing Equation
• Continuity of sediment discharge:
where is sediment concentration in riverbed; and are sediment discharge in x and y directions
• Sediment discharge equation: ATM
Governing Equation
• Sediment discharge equation: MPM
where:
qB is sediment discharge (m3/det), τ
c is the averaged
Simulation Scenario
Type
Cases Description Existing
of sabo works
Additional of sabo
works
Type 1
Type 2
Type Description
Type 1 There is no sabo work required to simulate with SIMLAR
Type 2 In this type, dimension of existing sabo work are: - Height : 7.5 m
- Width : 80 m
- Coordinate : 110°17’58.344”E 7°36’15.22” S - Sabo elevation : +388.339
Type 3 Additional sabo work required in this type besides existing of sabo work with classifications are:
Existing sabo dimension: - Height : 7.5 m
- Width : 80 m
- Coordinate : 110°17’58.344”E 7°36’15.22” S - Sabo elevation : +388.339
Additional sabo work dimension: - Height : 3.4 m
- Width : 60 m
Results : Discharge 1
• Without sabo works
• With
existing of sabo works
Discussions
• Sabo works could reduce the impacts of debris flows, especially for reducing velocity.
• In addition, sabo works have function as reservoir for sediment.
• However, if the sabo works have fulled by
sediment, sediment will flow out sabo works.
• If discharge of debris flow is not so high, river still could deliver flow from upper to lower
Result : Discharge 2
• Without sabo works
• With
existing of sabo works
Discussions
• If discharge of debris flow is very high, river
could ’t deli er flo fro upper to lo er area,
the area surrounding river is buried by sediment.
• Sabo works could reduce the area buried by sediment from debris flows.
• Additional sabo works could increase capacity for sediment, so the impact of debris flows could be reduced.
Conslusions
• Sabo works is effective to reduce the impact of debris flows.
