| Summary: | Lahar flow in region of Mount Merapi after an eruption of 2010 is still
considered potentially to happem and threat to the region around the river from
the upstream of Mount Merapi. The development of warning criteria against the
potential occurance of lahar flow is a thing that should be done continuoslu, with
regards to the dynamics data availability (rainfall data and lahar flow occurance
data), although with limited data. This study aims to find out of warning system
including snake line as a rain phenomenon in putih�s catchtment area which will
affect on the occurance of lahar flow, evaluate the success rate of snake line for
deciding the warning system. As a main reference to be used is Guidelines for
Development of Warning and Evacuation System Against Sediment Disasters in
Developing Countries yang diterbitkan oleh Ministry of Land, Infrastructure and
Transport Infrastructure Development Institute � Japan.
This research was conducted through several stages: preparation,
secondary data collection in the form of rainfall data, lahar flow occurance data,
analysis of rainfall which lead and does not lead into lahar flow, the making of
graph relations between rainfall intensity with working rainfall, determination of
critical line, warning line and evacuation line, depiction of snake line as well as
evaluation of snake line toward warning criteria being produced.
The results showed that the rainfall standard in Putih River: for warning
is 18 mm and for evacuation is 45 mm. The accuracy of warning criteria and
evacuation againts snake line for warning line is 30%, evacuation line is 61% and
critical line is 83%. The behavior of snake line that cause lahar flow in Putih
River, forming an angle 40o till 45o.
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