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)

Keduang 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.