Henky Nugraha, Henky
Master Program on Management Planning of Watershed and Coastal Area, Faculty of Geography, UGM

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Lahar at Kali Konto after the 2014 Eruption of Kelud Volcano, East Java: Impacts and Risk Dibyosaputro, Suprapto; Dipayana, Gilang Arya; Nugraha, Henky; Pratiwi, Kartika; Valeda, Hogy Prima
Forum Geografi Vol 29, No 1 (2015): Forum Geografi
Publisher : Forum Geografi

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Abstract

Five days after the Kelud Volcano eruption of 13 February 2014, lahar occurred in several channels of the Volcano. Rainfall with intensity of 26 mm/hour mobilized pyroclastic material from the upper slopes of Kelud Volcano down the channel during 3.5 hour. Using this eruption as a case study, the aims of this paper are (1) to study the geomorphic impact of lahars and (2) to study future hazards and risks due to the potential of lahar source material and lahar repose area. To reach these two goals, we use both primary and secondary data. The primary data comprises an integration of remote sensing, GIS approach, and fieldwork control, in order to investigate the geomorphic impacts of lahars. Secondary data were collected through interviews and statistical approach in villages, in order to determine their perception to the risk of lahar. Morphogenic processes such as riverbank erosion, channel-widening and riverbed downcutting took an important role in generating the impact of lahar in Kali Konto. The medial and distal areas were affected more largely affected than the proximal area. This major impacts have been river widening and buried crop field inside of the channel. This result allowed us to provide recommendation to population living along those areas at risk, in order to be prepared against the eventuality of potentially large and destructive lahars.
Lahar at Kali Konto after the 2014 Eruption of Kelud Volcano, East Java: Impacts and Risk Dibyosaputro, Suprapto; Dipayana, Gilang Arya; Nugraha, Henky; Pratiwi, Kartika; Valeda, Hogy Prima
Forum Geografi Vol 29, No 1 (2015): July 2015
Publisher : Universitas Muhammadiyah Surakarta

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Abstract

Five days after the Kelud Volcano eruption of 13 February 2014, lahar occurred in several channels of the Volcano. Rainfall with intensity of 26 mm/hour mobilized pyroclastic material from the upper slopes of Kelud Volcano down the channel during 3.5 hour. Using this eruption as a case study, the aims of this paper are (1) to study the geomorphic impact of lahars and (2) to study future hazards and risks due to the potential of lahar source material and lahar repose area. To reach these two goals, we use both primary and secondary data. The primary data comprises an integration of remote sensing, GIS approach, and fieldwork control, in order to investigate the geomorphic impacts of lahars. Secondary data were collected through interviews and statistical approach in villages, in order to determine their perception to the risk of lahar. Morphogenic processes such as riverbank erosion, channel-widening and riverbed downcutting took an important role in generating the impact of lahar in Kali Konto. The medial and distal areas were affected more largely affected than the proximal area. This major impacts have been river widening and buried crop field inside of the channel. This result allowed us to provide recommendation to population living along those areas at risk, in order to be prepared against the eventuality of potentially large and destructive lahars.
ANALISIS MORFOMETRI MENGGUNAKAN SISTEM INFORMASI GEOGRAFIS UNTUK PENENTUAN SUB DAS PRIORITAS (STUDI KASUS MITIGASI BENCANA BANJIR BANDANG DI DAS GARANG JAWA TENGAH) Nugraha, Henky; Cahyadi, Ahmad
Seminar Nasional Informatika (SEMNASIF) Vol 1, No 5 (2012): Geoinformatic And GIS
Publisher : Jurusan Teknik Informatika

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Abstract

Banjir bandang merupakan bencana yang sering terjadi di DAS Garang Jawa Tengah, dengan rata-rata?kejadian 2 kali dalam setahun. Oleh karena itu, diperlukan suatu kajian terkait mitigasi bencana banjir bandang?di DAS Garang agar risiko di masa mendatang dapat diminimalisir. Tujuan penelitian ini yaitu bertujuan untuk?memahami karakteristik hidrologi DAS Garang menggunakan Sistem Informasi Geografis (SIG) untuk?menentukan subDAS prioritas berdasarkan parameter morfometri sebagai upaya mitigasi bencana banjir?bandang. Data yang digunakan dalam penelitian ini meliputi data vektor jaringan sungai dan peta topografi?skala 1 : 25.000 terbitan Bakosurtanal. Metode yang digunakan adalah analisis morfometri DAS yang terdiri?dari Bifurcation Ratio (Rb), Drainage density (Dd), Stream Frequency (Fs), Texture Ratio (T), Basin Relief (Bh),?Relief Ratio (Rh), Ruggedness Number (Rn), Form Factor (Rf), Length of Overland Flow (Lof), dan Constant?Channel Maintenance (C) menggunakan sistem informasi geografis (SIG). Penentuan hubungan antar?parameter morfometri ditentukan dengan analisis korelasi menggunakan software SPSS 18. Parameter?morfometri terkait kemampuan menahan air ditumpangsusun untuk memperoleh nilai prioritas pengelolaan.?Hasil penelitian menunjukan bahwa subDAS Garang menjadi prioritas pertama untuk dikelola, dikuti dengan?subDAS Kreo dan subDAS Kripik dalam upaya mitigasi bencana banjir bandang di DAS Garang.
ANALISIS PENGARUH PERUBAHAN PENGGUNAAN LAHAN TERHADAP RETENSI POTENSIAL AIR OLEH TANAH PADA KEJADIAN HUJAN SESAAT (STUDI KASUS PERUBAHAN PENGGUNAAN LAHAN DI DAS GARANG JAWA TENGAH) Cahyadi, Ahmad; Yananto, Ardila; Wijaya, Muhammad Sufwandika; Nugraha, Henky
Seminar Nasional Informatika (SEMNASIF) Vol 1, No 5 (2012): Geoinformatic And GIS
Publisher : Jurusan Teknik Informatika

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Abstract

Tujuan penelitian ini adalah untuk mengetahui pengaruh perubahan penggunaan lahan di DAS Garang Jawa?Tengah Tahun 1994, 2001 dan 2008 terhadap retensi potensial maksimum air oleh tanah pada kejadian hujan?sesaat (storm rainfall). Metode yang digunakan adalah metode SCS yang dikembangkan oleh The Soil?Conservation Services. Data yang digunakan adalah data penggunaan lahan yang diekstrak dari citra Tahun?1994, citra 2001 dan citra 2008 menggunakan software ENVI dan peta tanah DAS Garang skala semi detail.?Hasil penelitian menunjukkan bahwa retensi potensial maksimum air oleh tanah pada kejadian hujan sesaat di?DAS Garang semakin menurun. Hal ini disebabkan semakin luasnya lahan terbangun dan semakin sempitnya?lahan non-terbangun. Kondisi ini akan menyebabkan imbuhan terhadap airtanah di DAS Garang semakin kecil?dan debit puncak banjir akan semakin besar.
USING REMOTE SENSING MULTI-TEMPORAL IMAGE TO ANALYSE THE LAND USE CHANGES AND ITS IMPACT ON THE PEAK DISCHARGE IN GARANG WATERSHED CENTRAL JAVA Cahyadi, Ahmad; Nugraha, Henky; Nurjani, Emilya; Yananto, Ardila; Wijaya, Muhammad Sufwandika
Jurnal Matematika Sains dan Teknologi Vol 13 No 2 (2012)
Publisher : LPPM Universitas Terbuka

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Abstract

Perubahan penggunaan lahan di Kota Semarang akibat pertumbuhan penduduk dan aktivitas ekonomi telah menyebabkan terjadinya urban sprawl. Banjir rob, land subsidence, intrusi air laut dan tercemarnya air tanah di Kota Semarang Bagian Utara menyebabkan terjadinya perkembangan Kota Semarang dominan ke arah selatan. Hal ini menyebabkan perubahan penggunaan lahan dari lahan non terbangun menjadi lahan terbangun sehingga jumlah air hujan yang langsung menjadi limpasan akan semakin banyak. Hal ini akan menyebabkan bahaya banjir bandang di Kota Semarang semakin besar. Penelitian ini bertujuan untuk: (1) mengetahui perubahan lahan yang terjadi di DAS Garang selama tahun 1994 dan 2001, dan (2) mengetahui dampak perubahan penggunaan lahan terhadap besarnya debit puncak yang terjadi di DAS Garang. Data yang digunakan dalam penelitian ini adalah Citra Landsat TM tahun 1994, Citra Landsat ETM tahun 2001, dan Citra Alos AVNIR 2008, peta tanah DAS Garang, peta kemiringan lereng DAS Garang, peta jaringan sungai DAS Garang, dan data curah hujan harian Stasiun Ungaran tahun 1952 sampai dengan tahun 2009. Ditemukan bahwa luas lahan terbangun bertambah lebih dari dua kali lipat dari tahun 2001 sampai dengan 2008, lahan pertanian meningkat hampir 50% dan luas hutan mengalami penurunan dari tahun ke tahun. Namun demikian, debit puncak di DAS Garang tidak bertambah secara ekstrem meskipun mengalami sedikit perubahan. Change due to land use in the city of Semarang as an impact of population growth and economic activity has led to urban sprawl. Rob flooding, land subsidence, seawater intrusion and contamination of ground water in the northern part of Semarang lead to the development of the southern part. Consequently, this leads to changes in land use so that the amount of rain water runoff will increase. This may cause the danger of flash floods in the greater city of Semarang. This study were aimed to: (1) determine the changes that occur in the Garang watershed lands during 1994 and 2001, and (2) determine the impact of land use changes on the size of the peak discharge occurring in the Garang watershed. The data used in this study were the 1994 Landsat TM, Landsat ETM 2001, and Citra Alos AVNIR 2008, Garang watershed soil map, slope map of Garang watershed stream network, and daily rainfall data at Ungaran Station of 1952 until 2009. It was found that developed land has been increasing more than doubled from 2001 to 2008, agricultural land increased by nearly 50% and the forest area were decreased from year to year. However, the peak discharge at the Garang watershed has not increased to the extreme though there was a slight change.