Information on the time and location of debris flow initiation is essential
for planning preventive measures and evacuation systems. To predict the time
and location of debris flow initiation, we applied a method that combines the
kinematic wave method and the index proposed by Takahashi (1978). The method
was tested with data from the Boyong River at Merapi Volcano, Indonesia, and
the Nojiri River at Sakurajima Volcano, Japan. A new diagram was also developed
to show temporal and spatial variations in Takahashi's index in relation to
temporal variation in rainfall intensity and discharge rates, and spatial variation
in the slope gradient, catchment area, width of channel, and depth of surface
flow along the main channel. Four specific debris]flow occurrences were analyzed.
For the Boyong River, the proposed method correctly predicted debris flow initiation
at rainfall intensity peaks for a stretch of river lying 2,150 ]3,679 m from
the summit, with slope gradients between 14 and 17. For the Nojiri River,
the method correctly predicted debris flow initiation at rainfall intensity
peaks for stretches of river 520 ] 735 m and 1,422 ] 1,777 m from the summit,
with slope gradients between 10.2 and 17.9.
Key wordsFdebris flow, initiation area, kinematic wave method, critical index