ANALISA KERUNTUHAN BENDUNGAN MAMAK DAN BENDUNGAN BATU BULAN SECARA SIMULTAN PADA SISTEM PENGALIRAN SUNGAI DENDITRIK
Abstract
Abstrak : Bendungan Mamak dan Batu Bulan yang termasuk dalam sistem pengaliran sungai denditrik dan berlokasi di Kabupaten Sumbawa, Propinsi Nusa Tenggara Barat telah disimulasikan runtuh secara simultan. Keruntuhan tersebut berdampak bagi tergenangnya 15 Desa, di 4 Kecamatan dengan jumlah penduduk yang terkena resiko diperkirakan mencapai 12.803 jiwa. Berdasarkan SK Dirjen SDA PU, tahun 2011 Bendungan Mamak dan Batu Bulan diklasifikasikan Bahaya Sangat Tinggi.
Peneitian ini membuktikan bahwa keruntuhan bendungan secara simultan pada sistem aliran sungai denditrik ataupun series saat ini dapat dilakukan dengan bantuan perangkat lunak Zhong Xing HY21 (User Manual Zhong Xing-HY21, Sinotech Engineering Group, 2011). Hal ini sekaligus menepis pendapat sementara para ahli sebelumnya yang beranggapan bahwa hal tersebut sulit dilakukan.
Kerapatan jaring-jaring kerja juga memiliki pengaruh besar terhadap tingkat ketelitian hasil penelusuran banjir di hilir. Pada penelitian kali ini kerapatan jaring-jaring di alur sungai dibuat lebih rapat daripada bagian di luar alur sungai utama. Dengan asumsi sebelum banjir menggenangi wilayah bantaran sungai, banjir terlebih dahulu akan memenuhi alur sungai utama. Namun hal tersebut membawa konsekuensi bahwa makin rapat jaring-jaring kerja, proses simulasi membutuhkan waktu lebih lama.
Kata kunci: Keruntuhan, Denditrik, Simultan, Zhong Xing HY21, Jaring-Jaring Kerja
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Abstract : Mamak and Batu Bulan Dams included dendritic river system, located in Sumbawa District and West Nusa Tenggara Province, have been simulated simultaneous failure. This failure impact on flood inundation in 15 Villages and 4 Subdistrics with estimated population at risk 12.803 persons. Based on National Regulation (SK Dirjen SDA PU, year 2011), the dams were classified into High Risk Dam.
This research proves that nowadays the simultaneous dams failure in dendritic river system and also series system could be simulated by using Zhong Xing HY21 (User Manual Zhong Xing-HY21, Sinotech Engineering Group, 2011). This study also reject previously temporary experts opinion that assumed it is difficult to do.
Density of the finite element mesh also has a big influence in the unsteady flow accuration result. In the present study the density of the mesh in the river flow is made more dense than the outside of the main river channel. Assuming before floods inundated the area along the river, the floods will first meet the main river channel. However, this setting has consequences that the more tightly the mesh, the simulation process takes longer.
Key words: Failure, Dendritic, Simultaneous, Zhong Xing HY21, Mesh
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