ANALISIS DEBIT BANJIR RANCANGAN DENGAN METODE HIDROGRAF SATUAN SINTETIS NAKAYASU DI SUB DAS KEDUANG (Analysis of planned flood discharge using the Nakayasu synthetic unit hydrograph in Keduang Sub Watershed) - Esa Bagus Nugrahanto; Slamet Suprayogi; Mohammad Pramono Hadi; Rissa Rahmadwiati (Jurnal Penelitian Pengelolaan Daerah Aliran Sungai (Journal of Watershed Management Research), 2022)
ABSTRAKSub DAS Keduang merupakan daerah yang rawan terjadi bencana banjir. Hal ini terjadi karena tutupan lahan yang variatif diikuti dengan tutupan hutan yang rendah. Keadaan ini menyebabkan peningkatan air limpasan yang berpotensi menjadi banjir. Penelitian ini bertujuan untuk menganalisis debit banjir rancangan di Sub DAS Keduang dengan beberapa periode ulang. Penelitian dilakukan dengan analisis data sekunder tahun 2007-2018. Analisis curah hujan dilakukan dengan beberapa metode, yaitu metode normal, log normal, log pearson III, dan gumbel serta diuji dengan uji chi square dan kolmogorov smirnov. Analisis debit banjir rancangan menggunakan metode HSS Nakayasu. Hasil penelitian diperoleh bahwa analisis curah hujan yang dipilih adalah metode normal. Debit banjir rancangan diperoleh bahwa debit maksimum periode ulang 2 tahunan adalah 1.375,20 m3/detik, periode ulang 5 tahunan sebesar 1.724,92 m3/detik, periode ulang 10 tahunan 1.908,10 m3/detik, periode ulang 20 tahunan 2.057,97 m3/detik, periode ulang 25 tahunan 2.087,12 m3/detik, periode ulang 50 tahunan 2.228,67 m3/detik, periode ulang 100 tahunan 2.345,24 m3/detik, dan periode ulang 1000 tahunan sebesar 2.661,64 m3/detik. Hasil penelitian ini diharapkan dapat digunakan dalam perencanaan dan pengelolaan DAS untuk mitigasi bencana banjir di Sub DAS Keduang.Kata kunci: debit banjir rancangan, hidrograf satuan sintetis, nakayasu, analisis frekuensi, Sub DAS KeduangABSTRACTKeduang Sub Watershed was an area prone to flooding. This happens because of the varied land cover followed by low forest cover. This circumstance leads to an increase in runoff which has the potential to become flooded. This study aims to analyze the planned flood discharge in the Keduang Sub Watershed with several return periods. The study was conducted using secondary data analysis in 2007-2018. Rainfall analysis was performed by several methods, namely normal method, normal log, pearson III log, and gumbel and tested with chi square and kolmogorov smirnov tests. Planned flood discharge analysis was using the Nakayasu synthetic unit hydrograph method. Results showed that the rainfall analysis chosen is normal method. The planned flood discharge obtained that the maximum discharge of the 2-yearly return period was 1,375.20 m3/s, the 5-yearly return period was 1,724.92 m3/s, the 10-yearly return period was 1,908.10 m3/s, the 20-yearly return period was 2,057.97 m3/s, the 25-yearly return period was 2,087 m3/s, the 50-yearly return period of 2,228.67 m3/s, the 100-yearly return period of 2,345.24 m3/s, and the 1000-yearly return period of 2,661.64 m3/s. Flood discharges are increasing in the larger return period, and the largest flood discharge occurred in the 1000-yearly return period. The results of this study are expected to be used in watershed planning and management for flood disaster mitigation in Keduang Sub Watershed.Keywords: planned flood discharge, synthetic unit hydrograph, nakayasu, frequency analysis, Keduang Sub Watershed