KARAKTERISTIKA INISIASI ALIRAN LAHAR TERPICU HUJAN DI SUNGAI VULKANIK

• Main Authors: , WASIS WARDOYO, , Prof. Dr. Djoko Legono, Ph.D
• Format: Theses and Dissertations NonPeerReviewed
• Published: [Yogyakarta] : Universitas Gadjah Mada 2014
• Subjects: ETD
• Online Access: https://repository.ugm.ac.id/128623/; http://etd.ugm.ac.id/index.php?mod=penelitian_detail&sub=PenelitianDetail&act=view&typ=html&buku_id=68980
• Institution: Universitas Gadjah Mada

Lahar occurs when the material deposits produced by volcano�s eruption is triggered by rainfall. The process of triggering occurs when deposits of material with a certain thickness and slope becomes saturated by rainfall accompanied with force imbalance due to surface runoff. Gendol River and some major rivers originating in the peak of Mount Merapi, was chosen as field study site due to the amounts of its deposit materials and its very dynamic rainfall characteristics. Till now, the rainfall characteristic that caused the lahar at this field has not been formulated yet. The objectives of this field research can be divided into two groups: the search for the relationship between rainfall intensity with flow condition and the relationship between rainfall intensity and working rainfall on lahar events in some major rivers. The first objective is reached by mounted Rainfall gauge and automatic camera on Gendol watershed. Automatic camera is used to observe the flow conditions in the river channel caused by recorded rainfall gauge. Data analysis was done to the characteristics of rainfall and the flow conditions in the Gendol River. The second is achieved by analysing the rainfall data and lava that occur in major rivers originating in the peak of Mount Merapi. The rainfall characteristics taken account in analysis are the depth of continuous rainfall, antecedent rainfall, working rainfall as well as rainfall intensity. In the analysis step, lava flows are grouped into two types of flow, namely debris flow and immature debris flow based on the characteristic sediment diameter and slope of the river channel. Several conclusions can be drawn as a result of the data analysis field as follows. The surface runoff at the river appears when the rainfall intensity is greater than 22 mm/hour. The initiation of sediment movement occurs when the rain intensity over 36.40 mm/hour. Immature debris flow occurs if there are continous rainfall with working rainfall greater than 100 mm and rainfall intensity greater than 22 mm/hour. Debris flow occurs if there are a continous rainfall with the working rainfall greater than 300 mm and rainfall intensity greater than 22 mm/hour. Both types of debris only occurred if at least one of the day of the continuous rainfall events having depth greater than 50 mm.