Pemodelan Aliran Debris Pada Kali Mujur Akibat Erupsi Gunung Semeru di Kabupaten Lumajang

Fawati, Isroul Akbar (2026) Pemodelan Aliran Debris Pada Kali Mujur Akibat Erupsi Gunung Semeru di Kabupaten Lumajang. Masters thesis, Institut Teknologi Sepuluh Nopember.

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Abstract

Kali Mujur merupakan salah satu sungai utama alami berhulu di Gunung Semeru yang berfungsi sebagai jalur utama aliran material vulkanik, sehingga Kali Mujur berpotensi besar terjadi banjir lahar dingin. Salah satu sabodam di sepanjang aliran Kali Mujur, Sabodam Klerek mengalami kerusakan akibat diterjang banjir lahar dingin dari Gunung Semeru. Kerusakan pada sabodam mengindikasikan adanya ketidaksiapan infrastruktur dalam menampung volume dan kecepatan aliran debris. Kompleksitas karakteristik aliran debris yang berdampak kerusakan, memerlukan kajian dengan memperhitungkan partikel debris yang menjadi keterbaharuan penting dalam studi ini. Penelitian ini bertujuan menganalisis karakteristik banjir debris di Kali Mujur serta mengevaluasi efektivitas alternatif mitigasi struktural. Hasil analisis menunjukkan bahwa kurva hidrograf aktual pada kejadian hujan 7 Juli 2023 memiliki debit puncak sekitar 390 m³/detik pada pukul 05.00. Validasi model dilakukan dengan membandingkan elevasi muka air hasil simulasi terhadap kondisi lapangan. Dengan konsentrasi sedimen (Cd) sebesar 0.25, model reologi Bingham menggunakan parameter yield strength 150 Pa dan Mixture Dynamic Viscosity sebesar 1,48 Pa-s mampu merepresentasikan kondisi lapangan dengan baik. Pada kondisi erupsi, bangunan sabo dam mengalami kerusakan yang signifikan akibat tingginya energi aliran debris. Oleh karena itu, pada perencanaan sabo dam yang baru, infrastruktur intake ditempatkan pada lahan kosong di sisi bendung untuk menghindari paparan langsung aliran debris. Sedangkan fungsi utama sabo dam difokuskan pada pengendalian aliran debris melalui peningkatan dimensi mercu. Upaya ini bertujuan untuk meningkatkan kapasitas bangunan dalam menahan dan mengendalikan material vulkanik. Namun, hasil pemodelan menunjukkan bahwa peningkatan dimensi mercu, belum mampu mencegah terjadinya limpasan banjir pada area bendung. Sehingga direncanakan alternatif kedua berupa penambahan tanggul dengan elevasi 167 m, sebagai upaya untuk membatasi penyebaran aliran debris agar tetap berada dalam alur sungai. Berdasarkan hasil pemodelan berbagai skenario, kombinasi peningkatan dimensi mercu sabo dam dan pembangunan tanggul merupakan alternatif mitigasi struktural yang paling efektif dalam menurunkan dampak aliran debris. Pembangunan tanggul dengan tinggi 1.5 m di hulu sabo dam mampu mengurangi potensi limpasan yang melewati bendung, memperkecil luas genangan banjir di sekitar area bendung, serta meningkatkan perlindungan terhadap infrastruktur di sekitarnya.
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Kali Mujur is one of the major natural rivers originating from Mount Semeru and serves as the primary channel for volcanic debris transport, making it highly susceptible to debris floods. One of the sabo dams along the Kali Mujur, Klerek Sabo Dam, was severely damaged by debris floods triggered by the Mount Semeru eruption. This damage indicates that the existing infrastructure was unable to withstand the volume and flow energy of the debris flood. The complex characteristics of debris flows require detailed investigation, particularly by considering the influence of debris particles, which represents the main novelty of this study. This study aims to analyze the characteristics of debris floods in Kali Mujur and evaluate the effectiveness of structural mitigation measures. The results show that the observed hydrograph during the rainfall event on 7 July 2023 reached a peak discharge of approximately 390 m³/s at 05:00. Model validation was performed by comparing the simulated water surface elevations with field observations. With a sediment concentration coefficient (Cd) of 0.25, the Bingham rheological model, using a yield strength of 150 Pa and a mixture dynamic viscosity of 1.48 Pa·s, successfully reproduced the observed field conditions. Under eruption conditions, the existing sabo dam experienced significant damage due to the high energy of the debris flow. Therefore, in the proposed sabo dam redesign, the intake structure is relocated to an open area adjacent to the weir to minimize direct exposure to debris flow. Meanwhile, the primary function of the new sabo dam is focused on debris flow control by increasing the crest dimensions, thereby improving its capacity to retain and regulate volcanic material. However, the simulation results indicate that increasing the crest dimensions alone is insufficient to prevent overtopping at the weir. Consequently, a second mitigation alternative is proposed by constructing levees with a crest elevation of 167 m to confine the debris flow within the river channel and limit its lateral spreading. Based on the simulation results from various scenarios, the combination of an increased sabo dam crest and levee construction provides the most effective structural mitigation strategy for reducing debris flow impacts. A 1.5 m-high levee in upstream of sabo dam effectively prevents overtopping at the weir, reduces flood inundation around the weir area, and improves the protection of surrounding infrastructure.

Item Type:	Thesis (Masters)
Uncontrolled Keywords:	Debris, Sabodam, HEC-RAS, Kali Mujur, Gunung Semeru, Debris, Mujur River, Semeru Mountain
Subjects:	T Technology > TC Hydraulic engineering. Ocean engineering > TC167 Dams, reservoirs T Technology > TC Hydraulic engineering. Ocean engineering > TC530 Flood control
Divisions:	Faculty of Civil, Planning, and Geo Engineering (CIVPLAN) > Civil Engineering > 22101-(S2) Master Thesis
Depositing User:	Isroul Akbar Fawati
Date Deposited:	30 Jul 2026 03:41
Last Modified:	30 Jul 2026 03:41
URI:	http://repository.its.ac.id/id/eprint/140373

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