Debris flow velocity due to the collapse of natural dam

Abstract

Natural dam on Way Ela river was a landslide formation of Ulakhatu mount located at Negeri lima village, Distric Leihutu, Ambon island on 13th July 2012. The natural dam blockage the valley for 300 m wide and 200 m height with total 1,000 m dam area and providing 87 million m3 volume of water storage. Slope failure trigger by slide area on the deeper surface structure leading to landslide. High risk landside increased by the high rainfall intensity of 432 mm/day and causing the failure of natural dam Way Ela. This study aimed to analyse debris flow velocity of the landslide of natural dam. Analysis performed based on debris during using geometric slope with empirical model system. PMF Syndrer-Alexeyev and GAMA-1 method and PMP frequency analysis equation method demonstrated that rainfall intensity data along with recurrent period of 100 years of Qpeak resulting debit volume of 448.85 m3/d. Furthermore, velocity estimation also showed that on 215.66 elevation high, allowable slope degree of (i) 0,005 %, average width of Way Ela river of 79.97 m and Manning’s grain roughness of 0.004 μm would resulting debris flow velocity of 10.98 m/s, and distance from the landslide centre point to the river mouth was 2.5 km. Those data leading to achieve arrival flow time to the residential area of 3.8 minutes. This study results potential as a base data for disaster mitigation due to high risk of debris flow velocity presented by Way Ela river.

Analisis Laju Angkutan Sedimen Di Sungai Luas Bengkulu Dengan Menggunakan Metode Shen Hungs Dan Engelund Hansen

“…Sedimen merupakan produk disintegrasi dan dekomposisi batuan (Hambali et al, 2016). Disintegrasi merupakan proses dimana batuan yang rusak/pecah menjadi butiran-butiran kecil tanpa perubahan substansi kimiawi (Salahuddin et al, 2020). Sedangkan dekomposisi mengacu pada pemecahan komponen mineral batuan oleh reaksi kimia yang mencakup proses karbonasi, hidrasi, oksidasi dan solusi (Nugraha, 2019).…”