RETARDING BASIN MODELING FOR LAHAR HAZARD MANAGEMENT (Case Study in Bladak Catchment, East Java

ALZAENA ULYA RUSDIMI, Prof. Dr.rer.nat. Junun Sartohadi, M.Sc.

2015 | Tesis | S2 Geografi

DAS Bladak terletak di sebelah barat lereng gunungapi Kelud. Sungai Bladak memiliki potensi yang tinggi untuk dilewati banjir lahar dengan adanya material piroklastik dari letusan gunungapi Kelud pada bulan Februari, 2014 yang masih tertahan di hulu DAS. Kolam retensi adalah salah satu mitigasi bencana struktural yang dapat diimplementasikan untuk mengurangi resiko bencana lahar dan banjir bandang dalam lingkup DAS yang kecil. Tujuan dari penelitian ini adalah: (1) melakukan pemodelan kolam retensi dan mengevaluasi efektivitas dari keberadaan kolam retensi tersebut, dan (2) mengevaluasi lokasi yang sesuai dan efektivitas pembangunan retarding basin dalam mengurangi dampak bencana lahar, dan (3) untuk mengetahui penyesuaian yang dapat dilakukan pada penggunaan lahan dan pemilihan lokasi kolam retensi berdasarkan rencana tata ruang wilayah. Pemodelan kolam retensi dilakukan dengan menggunakan model hidrologis Limburg Soil Erosion Model (LISEM) dan PCRaster dengan analisis spasial menggunakan ArcGIS 10.1. Evaluasi penggunaan lahan di DAS Bladak berdasarkan pada Rencana Tata Ruang Wilayah Kabupaten Blitar 2011-2031 dilakukan dengan pendekatan komparatif-deskriptif. Implementasi kolam retensi di sepanjang sistem drainase telah diketahui dapat menurunkan debit puncak meskipun dengan perbedaan yang kecil. Hasil ini dapat terkait dengan ukuran dan jumlah kolam retensi yang dimodelkan dalam DAS kajian. Evaluasi penggunaan lahan di DAS Bladak menunjukkan adanya penyimpangan dari penggunaan lahan di lapangan dengan yang diatur pada Rencana Tata Ruang Wilayah, sehingga menunjukkan perlunya peninjauan ulang terhadap rencana penggunaan lahan yang lebih komprehensif.

Bladak catchment is situated in the west side of Kelud volcanic slope. Bladak river has high potential to be overflown by lahars as most of the material deposits from the provious eruption in February, 2014 are still detained in its upstream. Retarding basin is one of structural mitigation measures that can be applied to reduce lahars and flash flood risk in a small catchment. The objectives of the research are: (1) to simulate rainfall-runoff generation in Bladak catchment using hydrological model, and (2) to investigate the preferable location for building retarding basin and its effectiveness to reduce lahars impacts, and (3) to suggest the possible adjustment on the land use and retarding basin locations with spatial planning principles. The rainfall-runoff simulation and retarding basin modeling are conducted by using hydrological model LISEM and PCRaster with spatial analysis using ArcGIS 10.1. Evaluation on the existing land use in Bladak catchment and the predermined spatial plan of Blitar Regency is conducted by comparative-descriptive approach. The rainfall-runoff simulation shows relevant result to the possibility of predicted site where excessive runoff might occur, which is highly influenced by the presence of its physical parameters. The implementation of retarding basin along the drainage system has been assessed to reduce the peak discharge in a small distinction. This result can be due to the size and number of the retarding basin applied in the catchment. The evaluation on land use in Bladak catchment shows some deviations on the presence land use with the predetermined spatial plan, which reflects the necessity to review land use planning to be more comprehensive. Bladak catchment is situated in the west side of Kelud volcanic slope. Bladak river has high potential to be overflown by lahars as most of the material deposits from the provious eruption in February, 2014 are still detained in its upstream. Retarding basin is one of structural mitigation measures that can be applied to reduce lahars and flash flood risk in a small catchment. The objectives of the research are: (1) to simulate rainfall-runoff generation in Bladak catchment using hydrological model, and (2) to investigate the preferable location for building retarding basin and its effectiveness to reduce lahars impacts, and (3) to suggest the possible adjustment on the land use and retarding basin locations with spatial planning principles. The rainfall-runoff simulation and retarding basin modeling are conducted by using hydrological model LISEM and PCRaster with spatial analysis using ArcGIS 10.1. Evaluation on the existing land use in Bladak catchment and the predermined spatial plan of Blitar Regency is conducted by comparative-descriptive approach. The rainfall-runoff simulation shows relevant result to the possibility of predicted site where excessive runoff might occur, which is highly influenced by the presence of its physical parameters. The implementation of retarding basin along the drainage system has been assessed to reduce the peak discharge in a small distinction. This result can be due to the size and number of the retarding basin applied in the catchment. The evaluation on land use in Bladak catchment shows some deviations on the presence land use with the predetermined spatial plan, which reflects the necessity to review land use planning to be more comprehensive.

Kata Kunci : Hydrological model, lahar management, retarding basin, LISEM, Bladak catchment