On 2018 September 28, 18:03 a local time (10:03 am UTC), the Mw 7.5 earthquake with a focal depth of about 20 km devastated the Palu region in Central Sulawesi, Indonesia resulting in a catastrophic disaster and many casualties. The Palu earthquakes triggered widespread landslides upstream, contributing to the sizeable material volume accumulated in rivers and mountain slopes. After the Palu earthquake, from September 28, 2018, until December 2021, at least 24 events of debris floods have occurred, which have spread to 15 villages. As of late, the empirical debris flow model Flow-R, software for susceptibility mapping of debris flows at a regional scale, was published. While Flow-R's applicability on a regional scale has been confirmed in several studies, the calibrated case using back-analysis of individual debris flow events in Indonesia based on DEMNAS with a spatial resolution of 8.3 m has never been conducted. Local debris flows modeling using Flow-R was evaluated with three well-documented debris flow events on the break slopes on the west and east sides of the Palu Valley. Quantitative analysis was carried out in this study to assess the accuracy, positive predictive value, and negative predictive value of models. First, the result shows the individual back-analysis model of debris flows found good agreement between debris-flow paths predicted and documented debris flow path extent. However, the parameters for rheological properties and erosion rate required in the software are limited. Second, the quantitative analysis shows accuracy, positive, and negative predictive value, which varies considerably. Based on the study, Flow-R is not suitable for comprehensive hazard mapping but provides a direct information about possible run-outdebris flow paths. Furthermore, lateral spreading and friction of Flow-R model results can be used to calibrate the process with rheological properties and erosion rate in other numerical modeling software, either for forward or back analysis.
Pusat Penelitian Geoteknologi LIPI ABSTRAK Prediksi bahaya gerakan tanah secara spasial dan temporal diperlukan untuk mitigasi bencana gerakan tanah. Makalah ini bertujuan untuk menyajikan hasil pemodelan tingkat kerentanan gerakan tanah dengan mempertimbangkan karakteristik lereng dan kekuatan tanah secara spasial dan curah hujan harian secara temporal di wilayah Kabupaten Sukabumi. Pemodelan menggunakan perangkat lunak TRIGRS untuk menghitung faktor keamanan lereng berbasis grid dengan ukuran 100 m x 100 m akibat infiltrasi air hujan. Hasil pemodelan menunjukkan tingkat kerentanan gerakan tanah spasial di Kabupaten Sukabumi dipengaruhi oleh topografi dan karakteristik keteknikan tanah. Sementara itu, curah hujan kumulatif menjadi faktor pengontrol penyebab perubahan tingkat kerentanan gerakan tanah temporal. Berdasarkan nilai faktor keamanan lereng, daerah dengan kerentanan gerakan tanah
ABSTRAK Makalah ini mengkaji penggunaanband termal citra Landsat 7 dan 8 sebagai metode tidak langsung dalam mengidentifikasi kehadiran keluaran airtanah lepas pantai (KALP) di perairan utara Pulau Lombok. Langkah pengolahan citra meliputi koreksi atmosferik, pemerolehan nilai suhu efektif, anomali suhu efektif, dan anomali suhu efektif standar serta penajaman citra. Peta anomali suhu efektif standar memiliki pola yang lebih bervariatif dibandingkan peta suhu efektif. Namun keduanya belum dapat menunjukkan suhu ekstrim yang mengindikasikan lokasi KALP. Parameter anomali suhu efektif standar tidak dapat dipergunakan sebagai variabel tunggal. Identifikasi lokasi KALP di daerah tropis membutuhkan data citra dengan resolusi spasial yang lebih detail. Pemanfaatan data citra juga perlu memperhatikan waktu perekaman citra yaitu pada saat kondisi perairan hangat untuk kasus KALP bersuhu rendah dan pada saat air surut.
ABSTRAKAnalisis morfometri Daerah Aliran Sungai (DAS) pada dua DAS mikro (Cibintinu dan Cibodas) dilakukan untuk mengetahui karakteristik kedua DAS tersebut. 15 parameter morfometrik yang dihitung meliputi orde sungai, jumlah sungai, panjang sungai, panjang rata-rata sungai, rasio panjang sungai, rasio bifurkasi, rasio bifurkasi rerata, kerapatan drainase, tekstur trainase, frekuensi sungai, rasio relief, faktor bentuk, rasio elongasi, rasio sirkularitas, dan panjang aliran permukaan. Longsoran besar terjadi pada tanggal 14 Oktober 2016 di DAS mikro Cibintinu sedangkan rayapan masih terus terjadi di DAS mikro Cibodas. Kedua DAS mikro tersebut saling berdampingan dan berada dalam satu sub DAS, yaitu sub DAS Cibintinu. Tujuan penelitian ini untuk mengetahui perbedaan karakter DAS pada kedua DAS mikro tersebut. Analisis morfometri DAS dilakukan dengan menggunakan bantuan SIG (Sistem Informasi Geografis). Data yang digunakan adalah data DEM Terrasar-X dengan resolusi spasial 9 meter serta peta dasar. Hasil analisis menunjukkan bahwa DAS mikro Cibintinu merupakan DAS yang berbentuk memanjang dengan tahap geomorfik muda sedangkan Cibodas merupakan DAS yang berbentuk bulat yang telah mengalami tahap geomorfik lanjut. Hal ini dapat dijadikan masukan untuk penelitian lebih lanjut untuk mengetahui ada tidaknya keterkaitan antara tahapan geomorfik suatu DAS dengan tipe longsoran. Kata kunci: morfometri DAS, SIG, gerakan tanah ABSTRACTWatershed morphometric analysis on two micro watersheds (Cibintinu and Cibodas) was done to evaluate those watershed characteristic. 15 morphometric parameters i.e stream order, stream number, stream length, mean stream length, stream length ratio, bifurcation ratio, mean bifurcation ratio, drainage density, drainage texture, stream frequency, relief ratio, form factor, elongation ratio, circularity ratio, length of overland flow; were calculated in this study. Major landslide occurred on October 14, 2016 in Cibintinu micro watershed whereas the creep still continues to occur in the micro watershed of Cibodas. Both micro watersheds are side by side and are in a sub-watershed, Cibintinu sub watershed. The purpose of this research is to know the difference of watershed character in both micro watersheds. The morphometric analysis of the watershed was conducted using the help of GIS (Geographic Information System). The used data are DEM Terrasar-X data with 9 meter spatial resolution and base map. The results showed that Cibintinu micro watershed is an elongated watershed with young geomorphic stages while Cibodas is a circular watershed that has old geomorphic stages. This can be used as input for further research to determine whether there is a link between the geomorphic stages of a watershed with the type of mass movements.
A landslide inventory representing landslide locations is used as a key factor in landslide susceptibility assessment. This paper explores Google Earth (GE) for generating a polygon-based landslide inventory in Bandung Basin. How far GE can identify landslides and their boundaries, source areas, and types were discussed here. Visual interpretation of GE images supported by path tool in GE, official landslide reports, previous research papers, and media was performed. The result is a polygon-based landslide inventory consisting of 194 landslide areas and 194 landslide source areas during 1993-2020. The limitations of GE in preparing the landslide inventory are (1) not covering the timing of the landslide occurrences, (2) tricky to identify small landslides (<100 m2) in anthropogenically transformed areas, and (3) not able to distinguish between earth and debris of landslide material.
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