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Geological And Rainfall Condition As Landslide Causative Factors In Shoutern Part Of Central Java In Juni 2016 Rokhmat Hidayat; Samuel Jonson Sutanto; Moh. Deddy Munir
JURNAL TEKNIK HIDRAULIK Vol 7, No 2 (2016): JURNAL TEKNIK HIDRAULIK
Publisher : Pusat Litbang Sumber Daya Air, Kementerian Pekerjaan Umum dan Perumahan Rakyat

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1441.874 KB) | DOI: 10.32679/jth.v7i2.565

Abstract

On June 19, 2016, landslides occurred in some areas located in the South Central Java (Purworejo, Kebumen, and Banjarnegara). One day before the incident, there was a high intensity of rainfall in the surrounding areas. A study of the geological conditions as well as the characteristics of rainfall triggering those landslides has been carried out. Field investigations, geological analysis, and dailly to hourly rainfall analises have been conducted. Moreover, some necessary mitigation measures are discussed. The results of this study show that the main type of landslides is consisted of loosened components included in translational slides. The contact zone between weathered bedrocks and materials above causes the landslides. A porous soil in the top layer with fresh rock underneath may potentially be a sliding plane of this landslide. The different in soil thickness produces different landslide volume. Rainfall intensity during the landslide was 100-323 mm/day with intensity of 16-22 mm/hour for about 5 hours. Landslides occurred on the steep areas with slopes between 25-35. Generally, there are several measures that can be applied at the landslide sites, such as relocation of communities affected by landslides, and simple Early Warning System installed with rainfall sensor-based equipment
Pengaruh Intensitas Hujan Terhadap Kecepatan dan Tinggi Banjir Lahar Berdasar Permodelan SIMLAR 2.1 Rokhmat Hidayat; Akhyar Musthofa; Pedri Bahri
JURNAL TEKNIK HIDRAULIK Vol 8, No 2 (2017): Jurnal Teknik Hidraulik
Publisher : Pusat Litbang Sumber Daya Air, Kementerian Pekerjaan Umum dan Perumahan Rakyat

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (1813.781 KB) | DOI: 10.32679/jth.v8i2.482

Abstract

Large amount of active volcanoes distribution makes Indonesia a country vulnerable to lahar flow. Although lahar flow is categorized under volcanic eruption secondary disaster, it has large impacts in environmental, social, economic, infrastructure and casualties. For example, the incident of lahar flow disaster triggered by high rainfall was occurred in Putih River Magelang, on 24th January 201 . This study discusses the effect of rainfall intensity on lahar flow velocity and height. This study was carried out using a numerical model, SIMLAR 2.1, in Putih River, located on western slopes of Merapi Volcano, Magelang, Central Java. Modeling was performed by using several rain intensity scenarios, i.e. 60mm/hour, 70mm/hour, 80mm/hour, 90mm/hour and 100mm/hour. The velocity of lahar flow simulated by the model was validated using lahar flow velocity data from field measurement. The results showed that rainfall intensity has linear correlation with lahar flow velocity and height. Higher rainfall intensity results in higher lahar flow velocity and height. In addition, the modelling result also showed that the largest lahar flow velocity (2,88m/s) occurred when the rainfall was 100mm/hour and has a deviation of 17.71% compared to previous observations. In average, lahar height in the River increases around 24.31% when the rainfall increases 10 mm/hour.
DESIGN AND PRELIMINARY STUDY OF SUBSURFACE DRAINAGE IN HAMBALANG COMPLEX BOGOR Rokhmat Hidayat; Samuel Jonson Sutanto; Santosa Sandy Putra
JURNAL TEKNIK HIDRAULIK Vol 7, No 1 (2016): JURNAL TEKNIK HIDRAULIK
Publisher : Pusat Litbang Sumber Daya Air, Kementerian Pekerjaan Umum dan Perumahan Rakyat

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (7994.899 KB) | DOI: 10.32679/jth.v7i1.557

Abstract

The Pusat Pendidikan Pelatihan dan Sekolah Olah Raga Nasional (P3SON) construction project was conducted at Hambalang, Sentul, Bogor, West Java. The project area covers 32 hektares. The P3SON project is located at a small mountain, called Gunung Hambalang, which has steep slope and thick clay layer. Generally, Hambalang morphology has a slope of about 1045, and at some places the buildings are built on steep slopes with the degree of steepness more than 45. Based on to the bore log, the rock profile is silt rock with the deepness of 0-6 m, and under 6 m, there is a hard clay layer. Clay layer if it is in contact with water will become impermeable and thus swell. During the high intensity rainfall event, the landslide risk is high. In order to strengthen the slope stability, an outer subsurface drainage at the East side and also horizontal subsurface drainage system in the area itself are proposed. The twin iron pipes are designed for the East side drainage system with the diameter of 20-35 cm and laid 5 m under the surface elevation. Technically, there are fifteen locations that need horizontal drainage installation. Horizontal drainage pipes are designed with 10 cm diameter and 8 m interval between pipes. The length of the horizontal drainage pipes is 15-20 m with slope of 10. Due to the fact that the silt layer depth is 0-6 m, then the horizontal drainage pipes will be located in 3-5 m depth from the surface. Optimistically, this system will reduce the landslide risk in Hambalang area.
Analisis Stabilitas Lereng pada Longsor Desa Caok, Purworejo, Jawa Tengah Rokhmat Hidayat
JURNAL SUMBER DAYA AIR Vol 14, No 1 (2018)
Publisher : Bina Teknik Sumber Daya Air, Kementerian Pekerjaan Umum dan Perumahan Rakyat

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (3662.392 KB) | DOI: 10.32679/jsda.v14i1.195

Abstract

Landslide occurred on June, 19th 2016 in Caok Village, Purworejo,Central Java. Caok Village is part of Menoreh hills area. Most of Slope in the landslide location has more than 20o. Before the landslide, rain occurred with maximum intensity 325mm/day. This is an indication that landslide was triggered by groundwater infiltration process, caused by high rainfall intensity and steep slopes. In this research, slope stability analyzed using Plaxis and Geo-slope software. Data that are soil engineering properties, steep slope, and groundwater table modelling with Plaxis and Geo-slope software to obtain slope stability and deformation. Minimum number factor of safety is 1,25 (Bowless 1984), without earthquake. Safety factor 1,162 obtained from Geo-Slope model, while with Plaxis resulted 0,9522 with maximum displacement 205m. Both the results of safety factor indicate that the location of the study are prone to landslide.
BANJIR BANDANG DI ALASMALANG BANYUWANGI DAN ALTERNATIF PENANGANANNYA (Flash flood at Alasmalang Banyuwangi and alternatives for its completion) Rokhmat Hidayat; Jati Iswardoyo
Jurnal Penelitian Pengelolaan Daerah Aliran Sungai (Journal of Watershed Management Research) Vol 3, No 2 (2019): Jurnal Penelitian Pengelolaan Daerah Aliran Sungai (Journal of Watershed Managem
Publisher : Center for Implementation of Standards for Environmental and Forestry Instruments Solo

Show Abstract | Download Original | Original Source | Check in Google Scholar | Full PDF (942.901 KB) | DOI: 10.20886/jppdas.2019.3.2.127-140

Abstract

ABSTRACTFlash floods frequently occur in Indonesia. Flash flood can be caused by natural and human factors. This paper discusses the causes and mitigation of flash flood using a case study in Banyuwangi. On June 22th 2018, flash floods occurred in the residential areas of Garit, Karang Asem, and Bangunrejo Hamlets. Flash floods were triggered by heavy rainfall the day before, which reached 90 mm/day. The three hamlets are located in Alasmalang Village, Singojuruh Subdistrict, Banyuwangi District. The study began with a field survey, analysis of the damage, and the causes of a flash flood, and its alternative treatments. The suspected source of the material was the landslide material, approximately two million cubic meters from the Pendil Mountain. Some of the material were carried away by the river flooding caused flash floods in the three hamlets. The small width of the bridge was not able to be passed by trees and other flash flood material, so water overflowed the roads and houses. Based on the results of the study, it is recommended for disaster mitigation in the form of structural and non-structural actions. Structural measure in the form of bridge elevation and construction of sediment retaining weirs, while non-structural actions are in the form of an early warning system and dissemination of flash flood hazards.Keywords: Flash flood; landslide; structural treatments; non-structural treatments ABSTRAKBanjir bandang sering terjadi di Indonesia. Banjir bandang dapat disebabkan oleh faktor alami maupun manusia. Makalah ini membahas tentang penyebab dan mitigasi banjir bandang dengan studi kasus di Banyuwangi. Pada 22 Juni 2018 banjir bandang melanda kawasan permukiman di Dusun Garit, Karang Asem, dan Bangunrejo. Banjir bandang dipicu hujan lebat sehari sebelumnya mencapai 90 mm/ hari. Tiga dusun itu berada di Desa Alasmalang, Kecamatan Singojuruh, Banyuwangi. Penelitian diawali dengan survei lapangan, analisis kondisi kerusakan akibat banjir bandang, penyebab banjir bandang, serta alternatif penanganannya. Sumber material diduga berupa material longsor sekitar dua juta meter kubik dari Gunung Pendil. Sebagian material ini terbawa banjir sungai sehingga menyebabkan banjir bandang di tiga dusun tersebut. Kondisi lebar jembatan yang kecil tidak mampu dilalui oleh pepohonan dan material banjir lain, sehingga banjir meluap menggenangi jalan dan rumah warga. Berdasarkan hasil kajian maka direkomendasikan untuk penanggulangan dan mitigasi bencana berupa tindakan struktural dan tindakan non struktural. Tindakan struktural berupa peninggian jembatan dan pembangunan bending penahan sedimen, sedangkan tindakan nonstruktural berupa sistem peringatan dini dan sosialisasi bahaya banjir bandang.Kata kunci: Banjir Bandang; longsor; penanganan struktural; penanganan non-struktural