Longsor Edit (9)
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Geological Engineering DepartmentFaculty of Engineering
Dr. WAHYU WILOPO, S.T., M.Eng
BENCANA LONGSOR
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Geological Engineering DepartmentFaculty of Engineering
POKOK BAHASAN
• Definisi dan Jenis Longsor• Konsep Kestabilan Lereng Tanah• Proses dan Tahapan longsor• Konsep manajemen/ penanggulangan
bencana longsor
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Geological Engineering DepartmentFaculty of Engineering
• Longsoran : Gerakan tanah pada lereng melalui bidang gelincir lengkung atau lurus.
• Gerakan tanah : merupakan suatu gerakan menuruni lereng oleh massa tanah dan atau batuan, akibat dari terganggunya kestabilan tanah atau batuan penyusun lereng tersebut (Skempton & Hutchinson ,1969; Chowdhury, 1978; Varnes , 1978).
PENGERTIAN LONGSORAN DAN GERAKAN TANAH
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Geological Engineering DepartmentFaculty of Engineering
Klasifikasi Gerakan Tanah (Lee & John, 2004)
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Geological Engineering DepartmentFaculty of Engineering
Klasifikasi Gerakan Tanah (Lee & John, 2004)
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Geological Engineering DepartmentFaculty of Engineering
Types of Landslides
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Geological Engineering DepartmentFaculty of Engineering
JENIS MATERIAL (SEBELUM GERAKAN) JENIS GERAKAN TANAH BATUAN TANAH
FALLS (RUNTUHAN) - Rockfall (Runtuhan batuan) - Gerakan sangat cepat (ekstrim
cepat)
Runtuhan bahan rombakan Runtuhan tanah
ROBOHAN Robohan batuan Robohan bahan rombakan
Robohan tanah
Gerakan planar Gerakan rotasi Gerakan planar Gerakan rotasi SLIDES LONGSORAN
Slump Block glide Rock slide
Block glide debris
Slump earth flow
MATERIAL LEPAS
Fragmen Batuan
Pasir Lumpur Campuran Tanah Lumpur
Pejal non plastis Sangat plastis
Sand run Loessflow
Rapid earth flow
Mudflow
FLOWS (ALIRAN)
K E R I N G B A S A H
Rock fragment
flow
(Rock fall Avalanche)
Sand/silt flow
Debriss avalache
Debris flow
Slow earth flow
Mud flow
KOMPLEKS Gabungan dari bermacam gerakan tanah biasanya satu macam gerakan tanah lalu diikuti oleh macam gerakan tanah yang lain.
Klasifikasi Gerakan Tanah (Karnawati, 2006)
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Geological Engineering DepartmentFaculty of Engineering
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Geological Engineering DepartmentFaculty of Engineering
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Geological Engineering DepartmentFaculty of Engineering
Bagian-bagian dari Longsor
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Geological Engineering DepartmentFaculty of Engineering
KONSEP KESTABILAN LERENG
Kuat geser tanah (penahan)
Tegangan geser (penggerak)F =
Rumus di atas dapat dikembangkan dengan memasukkan parameter faktor pemicu, mis : kenaikan tekanan air pori karena infiltrasi dan percepatan gempabumi
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Geological Engineering DepartmentFaculty of Engineering
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Geological Engineering DepartmentFaculty of Engineering
Proses Terjadinya Gerakan Tanah
Faktor Pemicu•Air
•Getaran•Manusia
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Geological Engineering DepartmentFaculty of Engineering
Model mekanisme
kejadian longsor oleh
air
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Geological Engineering DepartmentFaculty of Engineering
Karakteristik Debris Flow
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Geological Engineering DepartmentFaculty of Engineering
Gejala Awal Gerakan Tanah
• Munculnya retakan lengkung memanjang pada lereng/ bangunan
• Terjadi amblesan tanah• Terjadi penggembungan pada lereng• Muncul rembesan air lumpur pada lereng• Pohon-pohon/ tiang-tiang miring• Berubahnya bentuk bangunan rumah• Terdengar suara gemuruh dari atas lereng, disertai
getaran.• Air sungai tiba-tiba keruh dan agak naik (gejala
banjir bandang).
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Geological Engineering DepartmentFaculty of Engineering
1. Lereng yang tersusun dari tumpukan tanah gembur
2. Lereng tersusun oleh perlapisan batuan miring ke arah luar lereng
3. Lereng tersusun dari batuan retak-retak
Ciri lereng rentan bergerak
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Geological Engineering DepartmentFaculty of Engineering
RAWAN LONGSOR
Tanah Yang GemburTanah Yang Gembur
Tanah Yang TebalTanah Yang Tebal
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Geological Engineering DepartmentFaculty of Engineering
Tumpukan batua dan pohon pohon yang tumbang potensi membentuk bendungan alam
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Geological Engineering DepartmentFaculty of Engineering
JATUHAN BATUAN
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Geological Engineering DepartmentFaculty of Engineering
Longsoran dan potensi debris flow (Galado) di Kanagarian Tanjung Sani, Kec. Tanjung Raya, Kab Agam
Jorong Pandan, Galapung, Batunanggai dan Muko
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Geological Engineering DepartmentFaculty of Engineering
Pemetaan Zona Resiko Longsor
• Parameter yang dipakai dalam analisis potensi dan risiko gerakan tanah meliputi parameter-parameter dari dua komponen berikut :
1.Komponen bahaya/hazard (faktor pengontrol)
2.Komponen kerawanan/vulnerability (kerugian)
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Geological Engineering DepartmentFaculty of Engineering
METODA ANALISIS BAHAYA (HAZARD) :
1. Metoda langsung (dengan pemetaan langsung di lapangan)
2. Metoda tidak langsung (metoda kuantitatif dan tumpang tinding dengan bantuan alat SIG)
–Berdasarkan kerapatan gerakan tanah–Berdasarkan analisis pembobotan dan
scoring
3. Metoda gabungan (metoda tidak langsung dan metoda langsung)
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Geological Engineering DepartmentFaculty of Engineering
Metoda tidak langsungUntuk skala kecil s/d menengah (< 1 : 25000)
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Geological Engineering DepartmentFaculty of Engineering
Metoda tidak langsung
• Skala detail (> 1 : 25 000)
• Metode ; dapat diterapkan salah satu metoda berikut :– Metoda Geomorfologi– Metoda analisis dengan Evaluasi Skor dan Bobot Total– Beberapa metoda/teknik analisis lain yang telah
dipublikasikan dalam journal ilmiah, atau yang dapat teruji secara akademik
– Metoda parsitisipasi masyarakat
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Geological Engineering DepartmentFaculty of Engineering
Metoda langsung
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Geological Engineering DepartmentFaculty of Engineering
Metoda gabungan
Metode ini menggabungkan dua peta yang telah dihasilkan yaitu hasil metode pemetaan tidak langsung dan metode pemetaan langsung kemudian ditumpangtindihkan (overlaying) sehingga menghasilkan peta final (peta gabungan).
Metode ini menggabungkan dua peta yang telah dihasilkan yaitu hasil metode pemetaan tidak langsung dan metode pemetaan langsung kemudian ditumpangtindihkan (overlaying) sehingga menghasilkan peta final (peta gabungan).
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Geological Engineering DepartmentFaculty of Engineering
KONSEP PEMETAAN RESIKO LONGSOR
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Geological Engineering DepartmentFaculty of Engineering
Zona Bahaya
• Zona potensi gerakan (zona kerentanan gerakan tanah, menurut SNI 13-7124-2005)
• Zonasi :– Potensi gerakan tinggi (sering terjadi gerakan)– Potensi gerakan menengah (dapat terjadi gerakan)– Potensi gerakan rendah(jarang terjadi gerakan)– Potensi gerakan sangat rendah (sangat jarang terjadi
gerakan)
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Geological Engineering DepartmentFaculty of Engineering
Peta Resiko Longsor Dengan Skala yang Tepat
• Skala regional untuk wilayah – nasional, – propinsi, – pulau – kabupaten).
• Skala lokal untuk wilayah :– kecamatan,– desa– kawasan
Dwikorita - UGM/2008
Utk menghindari kesalahan pengelolaan/ pembangunan lahan
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Geological Engineering DepartmentFaculty of Engineering
Skala
(dapat diterapkan metoda teknis lain)
(dapat diterapkan metoda teknis lain)
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Geological Engineering DepartmentFaculty of Engineering
Contoh peta
• Skala < 1 : 100.000 (peta-peta kerentanan gerakan tanah yang telah diterbitkan oleh DESDM)
• Skala > 100.000– Peta Teknis– Peta Non teknis (mengintegrasikan partisipasi
masyarakat di tingkat desa atau kecamatan)
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Geological Engineering DepartmentFaculty of Engineering
Skala 1 : 25000
• Metoda gabungan– Metoda langsung– Metoda tidak langsung
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Geological Engineering DepartmentFaculty of EngineeringMorphology of Piyungan-Patuk
Vertical exaggeration = 2.5
Leang Sop Heap & Karnawati , 2006
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Geological Engineering DepartmentFaculty of Engineering
Slope map
Leang Sop Heap & Karnawati , 2006
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Geological Engineering DepartmentFaculty of Engineering
Geological map
Leang Sop Heap & Karnawati , 2006
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Geological Engineering DepartmentFaculty of Engineering
Landuse map
Leang Sop Heap & Karnawati , 2006
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Geological Engineering DepartmentFaculty of Engineering
Verify landslide susceptibility map and landslide location map
Landslide susceptibility map Landslide location map
Leang Sop Heap & Karnawati , 2006
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Geological Engineering DepartmentFaculty of Engineering
Leang Sop Heap & Karnawati , 2006
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Geological Engineering DepartmentFaculty of EngineeringSource :
Leang Sop Heap & Karnawati, 2006
Leang Sop Heap & Karnawati , 2006
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Geological Engineering DepartmentFaculty of Engineering
Leang Sop Heap & Karnawati , 2006
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Geological Engineering DepartmentFaculty of Engineering
Strategi mensikapi alam & mencegah bencana???
• Mengabaikan/ ignorance ?• Menantang/ challenging ?• Menghindari/ avoiding ?• Menyesuaikan/ beradaptasi/ adapting ?
PENINGKATAN KETAHANAN
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Geological Engineering DepartmentFaculty of Engineering
Manajemen Bencana(menghindar atau beradaptasi)
• Analsis Resiko (Pemetaan zona kerentanan & kerawanan, kondisi ketahanan)
• Peningkatan ketahanan melalui :– Edukasi masyarakat/ cultural building for hazard
awareness– Penataan lahan dan lingkungan– Penegakan hukum– Pengembangan riset tepat guna– Pemantauan dan sistem peringatan dini
Dwikorita – UGM/2008
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Geological Engineering DepartmentFaculty of Engineering
Keberadaan UU RI no. 24 dan 26 tahun 2007 telah mengubah paradigma mitigasi bencana dari penanganan bencana menjadi penanggulangan bencana yang lebih menitikberatkan pada upaya-upaya sebelum terjadinya bencana.
Penataan Ruang dan wilayah yang memperhatikan aspek kebencanaan sangat tepat untuk diterapkan dalam rangka mengurangi dampak negatif akibat bencana.
Sebelum
Kejadian
Setelah
Kejadian
PENYELENGGARAAN BENCANA DAN MITIGASI BENCANA GERAKAN TANAH