CAPACITY OF SEDIMENT CONTROL STRUCTURE IN GENDOL RIVER

Eruption of Merapi mountain regularly occur in last twenty years. The eruptions caused pyroclastic flows, huge sediment and debris flows, threatening people live and assets in downstream area. Therefore, disaster management of debris flow will be easy to plan by conducting the research about capacity of sediment control structure in Gendol river. The research is based on sediment balance with transportable sediment volume analysis (VS) from empirical formula of Takahashi (1991) and Mizuyama (1977). Sediment balance was investigated based on maximum daily rainfall with minimum 10 years return period or known as (R24). At fact Gendol river has 22 km of river length and 14.86 km2 of catchment area. In 2016 there are 22 sabo dams have been built on Gendol river in order to anticipate the debris disaster and control the sediment. Based on the result of the research shows that the sabo dam can accommodate around 1165838.60 m3 of sediment. Compared with the estimation of debris flow volume about 1547899.16 m3. As the consequence there are around 382060.56 m3 sediment cannot be accommodate by the sediment control structure (sabo) in Gendol river. In conclusion sabo in Gendol river ineffective to mitigate the losses during debris flow. Therefore, in order to minimize the losses of sediment disaster the author recommend to build six sabo dams. The suggested sabo dam located on six different place along Gendol river