The Debris Flow Along Brungkah River, Pacitan, Indonesia, Caused by the Rainfall Incident of November 27, 2017

On November 27, 2017, a debris flow occurred in the Brungkah river, Pacitan, Indonesia, caused by extreme rainfall. Debris flow passed through and transported the sediment materials along the Brungkah river and stopped at the river confluence with the Grindulu river. The debris flow destroyed the main village access road to the Tukul dam and clogged the Grindulu river, the deposition area. Mapping on the ground surface and topographic cross sections along the Brungkah river area has been conducted to determine the source and volume of debris materials and the impact of debris flow. Results show the source of debris materials came from a previous wedge-shaped landslide with an area of approximately 2.6 ha, located upstream of the Brungkah river. The recurrence of landslides along the river has not been recorded well throughout history. The debris flow transported materials of sands and silts and various sizes of rocks by gravity flow to the deposition area. Using topographic cross sections, the volume of debris materials is estimated to be 78,000 m3.