Analisis Karakteristik Hujan Penyebab Aliran Debris Di Lereng Gunung Merapi

Caecilia Ajeng N, Prof. Dr. Ir. FatchanNurrochmad, M.Agr.

2013 | Tesis | S2 Teknik Sipil

Erupsi Gunung Merapi yang terjadi pada bulan Oktober sampai November 2010 memberikan ancaman bencana di wilayah lereng. Ancaman sekunder yang ditimbulkan oleh endapan material vulkanik di punggung Gunung Merapi yang bercampur dengan air hujan akan menjadi aliran debris. Aliran debris akan mengalir di alur sungai dengan kemiringan tertentu, akan menjadi aliran yang deras dan sangat berbahaya. Bahaya dan dampak yang diakibatkan oleh aliran debris khususnya di Kali Putih dan Kali Boyong sangat besar, sehingga diperlukan suatu penyelesaian yaitu prediksi mengenai aliran debris. Analisis karakteristik hujan penyebab aliran debris dilakukan dengan menggunakan metode Critical line curve yang diterbitkan oleh Ministry of Land, Infrastructure and Transport Infrastructure Development Institute – Japan metode tersebut didasarkan pada: rangkaian hujan penyebab aliran debris, working rainfall (RW), dan hujan efektif. Analisis karateristik spasial hujan yang akan digunakan di wilayah lereng Merapi menggunakan metode interpolasi spline. Hasil penelitian menunjukan bahwa hujan penyebab terjadinya aliran debris di Kali Putih bagian hulu minimum kedalaman hujan 47.5 mm dan intensitas hujan 14.75 mm/jam sedangkan di Kali Boyong bagian hulu kedalaman hujan 48 mm dan intensitas hujan 13 mm/jam. Berdasarkan pola spasial dengan metode interpolasi apabila dikaitkan dengan kedalaman hujan saat terjadi aliran debris 2010-2011, hujan di wilayah lereng Gunung merapi mempunyai variabilitas hujan yang tinggi.

Mount Merapi eruption that occurred on October to November 2010 gave threat of disaster to the slope area. The secondary threat came from the volcanic material deposit which will produce debris flow if mixed with storm water. The debris that flow down the slope or river bed with certain inclination will produce swift flow and become very dangerous. By considering the danger and the impact of this debris flow, and also reminding the limited data availability, it become necessary to find a simple method using rainfall data to forecast debris flow occurrence in slope of Mt. Merapi, especially in Putih River and Boyong River. Analysis to rainfall characteristic that induced debris flow was conducted using Critical line curve which published by Ministry of Land, Infrastructure and Transport Infrastructure Development Institute – Japan. This method is based on: rainfall series that induce debris flow, working rainfall (RW); and effective precipitation. Spatial analysis of rainfall in slope of Mt. Merapi was conducted using spline interpolation method. The research result shows that rainfall characteristic that induce debris occurrence in Putih River has minimum rainfall value in 47.5 mm and rainfall intensity in 14.75 mm/hour (upstream), whereas Boyong River has rainfall value in 48 mm and rainfall intensity in 13 mm/hour (upstream). By relating the spatial pattern using interpolation method with rainfall value on debris flow occurence in 2010-2011 shows that rainfall in Mt. Merapi has high rain variability.

Kata Kunci : aliran debris, working rainfall, Kali Putih, Kali Boyong