RAINFALL CHARACTERISTIC ON THE SLOPES OF MOUNT MERAPI REGION (EMPIRICAL FORMULA, DURATION, DISTRIBUTION, AND CRITICAL LINE WORO RIVER)
Abstract: Debris flow on the
slopes of Mount Merapi area became a serious natural disasters because it has
great destructive force and velocity. Rainfall with a certain intensity and
duration is one component triggering debris flow. Rainfall has variability of
the temporal and spatial characteristics influenced by various factors, such as
topography and climate. Dharma (2012) suggested to define the characteristics
of the intensity of rainfall using rainfall data with a shorter duration with
statistical tests to establish the best empirical IDF formula. This research was using of 30 minutes
rainfall data for short duration (<3 hours) and a spreadsheet software
representing duration and distribution of the rainfall. The most appropriate
rainfall intensity formula was done by the empirical IDF formula, i.e. Sherman,
Kimijima, Hasper and Mononobe. Rainfall intensity analysis applied Frequency
Analysis Software (based on Microsoft Excel). Debris flow occurrence was
analyzed using MLIT for method A to establish standard rainfall index. Sherman formula performed the best fit to the
IDF characteristics of rainfall in the region of the slopes of Mount Merapi.
Rainfall distribution pattern showed high intensity rainfall in the first hour
and then decreased in the next hour which means distribution for the duration
of 3 hours, 12%, 28%, 25%, 16%, 12%, and 7%, respectively with an interval of
30 minutes. Based on critical line, 5 mm of standard rainfall index was gained
in the case of warning (R1) and 28 mm in the case of evacuation (R2).
Author: Pudak Juni Laksana
Journal Code: jptsipilgg150045
