Author(s): N. Yulinsa; D. Legono; A. P. Rahardjo
Keywords: Mt. Merapi; 2010 Eruption; Putih River; Lahar Flow; Warning Criteri
Abstract: In many cases of disaster risk mitigation program, the availability of warning criteria has become more essential recently, simply because the structural approach such provision of physical countermeasures is insufficient. Similar situation also take place in the Mt. Merapi area, where the potential lahar flow occurrence increases significantly due to the huge number of sediment source after the 2010 eruption. The first lahar flow occurrence after 2010 eruption took place on 23January 2013 causing damage on several infrastructures including the national road which connects Yogyakarta Province and Central Java Province. Since then, small lahar flow occurrences took place in relatively small scales that damages were not so severe, except the loss of property due to sand mining activity. The potential lahar flow occurrence is highly affected by the instability of sediment deposit and this instability may increase significantly as trigged by high rainfall intensity. This paper deals with the development (applying the guideline issued by MLIT, 2004) of the lahar flow warning criteria at Putih River based on various observations the rainfall intensity at three rainfall stations in catchment area as well as lahar flow occurrence at Putih River. The information on continuous rainfall intensity and the working rainfall (i.e. rainfall taking into account previous 14 days rainfall) was used as the warning criteria development. The results of the development in the form of critical line, warning line, and evacuation line are performed, and the verification test using several rainfall phenomena in the form of snake line is also presented and discussed. The consistency of the snake line obtained from several rainfall phenomena suggests further application of warning criteria for the lahar disaster risk mitigation in Putih River area.