Lahar Flood Risk Assessment in Gendol and Opak Watershed, Yogyakarta, Indonesia

The aim of this research is, to assess the risk of lahar flood to the population in Gendol and Opak watershed using three parameters of risk, hazard, vulnerability, and coping capacity. Two scenarios are used in predicting the hazard area, with lahar volume and lahar discharge scenario.

The most extensive area which impacted by lahar flood in Gendol watershed, based on lahar volume scenario is 1562,26 ha compares to 1240,14 ha in Opak Watershed. Meanwhile, hazard assessment using lahar discharge scenario, total amount of  985.98 ha area of Gendol watershed are effected by lahar, compares to 625,85 ha in Opak Watershed.

Inhabitants of Dusun in Gendol watershed are more vulnerable to lahar flood. 6 villages in Gendol watershed has high until very high level of vulnerability, compares to 5 Villages in Opak watershed. But, the inhabitants of Villages in Opak Watershed have higher coping capacity. It proves by the number of villages with high until very high class of coping capacity, 19 villages in Gendol watershed and 25 in Opak watershed.

The differences in hazard level, vulnerability and coping capacity between to watersheds, bring differences in total affected inhabitants with high until very high risk. Based on lahar volume scenario, total of 10924 inhabitants has risk to lahar flood in Gendol watershed, compares to 7601 inhabitants in Opak watershed. Based on lahar discharge scenario, total 9991 inhabitants have risk to lahar flood in Gendol watershed, compares to only 504 inhabitants in Opak watershed.