ANALISIS SNAKE LINE UNTUK SISTEM PERINGATAN ALIRAN LAHAR DINGIN (STUDI KASUS KALI PUTIH, GUNUNG MERAPI)

Nina Yulinsa, Prof. Dr. Ir. Djoko Legono

2013 | Tesis | S2 Teknik Sipil

Aliran lahar dingin di wilayah Gunung Merapi paska erupsi 2010 dinilai masih berpotensi untuk terjadi, dan masih merupakan ancaman bagi kawasan di sekitar sungai yang berhulu dari Gunung Merapi. Pengembangan kriteria peringatan terhadap potensi terjadinya aliran lahar dingin merupakan hal yang harus dilakukan secara terus menerus, dengan memperhatikan dinamika ketersediaan data (hujan dan aliran), walaupun dengan data yang sangat terbatas. Penelitian ini bertujuan untuk mengetahui kriteria sistem peringatan dini termasuk perilaku garis ular (Snake Line) suatu fenomena hujan di DAS Putih yang berpengaruh terhadap kejadian aliran lahar dingin, mengevaluasi tingkat keberhasilan snake line untuk keputusan tindakan peringatan. Sebagai acuan utama akan digunakan Guidelines for Development of Warning and Evacuation System Against Sediment Disasters in Developing Countries yang diterbitkan oleh Ministry of Land, Infrastructure and Transport Infrastructure Development Institute – Japan. Penelitian ini melalui beberapa tahap yaitu persiapan, pengumpulan data sekunder yang berupa data curah hujan dan data kejadian aliran lahar dingin, analisis curah hujan yang menyebabkan aliran lahar dingin dan curah hujan yang tidak menyebabkan aliran lahar dingin, serta pembuatan grafik hubungan antara intensitas hujan dengan working rainfall, penentuan critical line, warning line dan evacuation line, penggambaran snake line serta evaluasi snake line terhadap kriteria peringatan yang dihasilkan. Hasil penelitian menunjukkan bahwa standar curah hujan untuk peringatan di Kali Putih sebesar 22 mm dan standar curah hujan untuk evakuasi adalah 49 mm. Keakuratan snake line terhadap kriteria peringatan dan evakuasi pada garis peringatan sebesar 30%, garis evakuasi sebesar 61%, garis kritis sebesar 83%. Perilaku snake line yang menyebabkan aliran lahar dingin di Kali Putih membentuk sudut antara 40o sampai dengan 45o.

Lahar flow in region of Mount Merapi after an eruption of 2010 is still considered potentially to happem and threat to the region around the river from the upstream of Mount Merapi. The development of warning criteria against the potential occurance of lahar flow is a thing that should be done continuoslu, with regards to the dynamics data availability (rainfall data and lahar flow occurance data), although with limited data. This study aims to find out of warning system including snake line as a rain phenomenon in putih’s catchtment area which will affect on the occurance of lahar flow, evaluate the success rate of snake line for deciding the warning system. As a main reference to be used is Guidelines for Development of Warning and Evacuation System Against Sediment Disasters in Developing Countries yang diterbitkan oleh Ministry of Land, Infrastructure and Transport Infrastructure Development Institute – Japan. This research was conducted through several stages: preparation, secondary data collection in the form of rainfall data, lahar flow occurance data, analysis of rainfall which lead and does not lead into lahar flow, the making of graph relations between rainfall intensity with working rainfall, determination of critical line, warning line and evacuation line, depiction of snake line as well as evaluation of snake line toward warning criteria being produced. The results showed that the rainfall standard in Putih River: for warning is 18 mm and for evacuation is 45 mm. The accuracy of warning criteria and evacuation againts snake line for warning line is 30%, evacuation line is 61% and critical line is 83%. The behavior of snake line that cause lahar flow in Putih River, forming an angle 40o till 45o.

Kata Kunci : aliran lahar dingin, kriteria peringatan, working rainfall, snake line, Kali Putih, lahar flow, warning criteria, working rainfall, snake line, Putih River