PERENCANAAN CHECK DAM AMPELGADING SEBAGAI UPAYA PENGENDALIAN BANJIR LAHAR DINGIN GUNUNG SEMERU PADA SUNGAI GLIDIK KECAMATAN TEMPURSARI KABUPATEN LUMAJANG

Yuangga Rizky Illahi, Sumiadi Sumiadi

Abstract


ABSTRAK: Aktifitas vulkanologi yang tinggi pada gunung Semeru mengendapkan material vulkanik di sekitar kawah. ketika hujan, material akan terbawa bersama banjir menjadi banjir lahar dingin (aliran debris) di sungai. Sungai Glidik menjadi salah satu sungai yang terlewati banjir lahar dingin dan terkena dampak kerusakan apabila tidak dikendalikan. Perhitungan hidrologi menggunakan metode Hidrograf Satuan Sintesis Nakayasu menunjukkan debit Q25th 1059.49 m3/dt dan Qdesain = 1.265 x Q25th = 1340.74 m3/dt. Perbandingan peta topografi tahun 2013 dan 2017 menunjukkan perubahan sedimen sebesar 15703.89 m3/thn tergerus dan 13725.61 m3/thn terendap pada lokasi. Lokasi alternatif rencana A dipilih daripada lokasi alternatif rencana lainnya karena memiliki perbandingan pengurangan slope dasar sungai terbesar, perbandingan panjang : volume tampungan terbesar, dan jenis aliran yang dominan aliran debris. Check dam direncanakan dengan tinggi 2.5 m, lebar pelimpah 150 m, lantai olak, sub dam, dan dikontrol dengan analisa stabilitas. Analisa rencana anggaran biaya menunjukkan total nilai pekerjaan senilai Rp. 20.97 Milyar.

 

Kata Kunci: gunung semeru, banjir lahar dingin, sungai glidik, check dam

ABSTRACT: High volcanology activities on mount Semeru deposit volcanic material around the crater. When it rains, materials will carried along with the flood become cold volcanic mudflow (debris flow) in river. Glidik river is one of rivers that has been flooded by cold volcanic mudflow and affected by damage if not controlled. Hydrology calculation using Synthetic Hydrograph Unit Nakayasu method shows discharge Q25yr 1059.49 m3/s and Qdesign= 1.265 x Q25yr = 1340.74 m3/s. Comparison of topographic maps between years 2013 and 2017 shows sediment changes by 15703.89 m3/yr eroded and 13726.61 m3/yr deposited on site. Alternative site plan A chosen than other alternative site plan because have biggest slope river base changing comparison value, biggest long : sediment storage volume comparison value, and debris flow as flow type dominant. Check dam is planned by 2.5 m high, 150 m wide of spillway, hydraulic jump floor, sub dam, and controlled by stability analysis. Budget plan analysis shows total value of work worth Rp. 20.97 Billions.

Keywords: mount semeru, cold volcanic mudflow, glidik river, check dam

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