Analisis pengaruh perubahan tata guna lahan pada debit banjir rancangan di DAS Serayu

Land use change is one of the main factors influencing watershed hydrological response, particularly flood discharge characteristics. This study aims to analyze the effect of land cover changes on design flood discharge in the Serayu Watershed for the years 2015, 2019, and 2024. Land cover data were derived from Landsat 8 satellite imagery and processed using supervised classification to obtain composite Curve Number (CN) values. Hydrological analysis was conducted by determining 20-year return period design rainfall using the Log Pearson Type III distribution, calculating effective rainfall with the SCS-CN method, and estimating flood discharge using Synthetic Unit Hydrograph (SUH) methods of Soil Conservation Service (SCS) and Nakayasu. The results show a gradual increase in composite CN values from 78,13 in 2015 to 78,19 in 2019 and further increase 78,22 2024, indicating reduced infiltration capacity due to land cover changes. This condition resulted in an increase in peak flood discharge. The peak discharge for the 20-year return period calculated using the SCS method with Alternating Block Method distribute rainfall increased from 3878,65 m³/s in 2015 to 3890,55 m³/s in 2024, while the Nakayasu method with Tadashi Tanimoto distribute rainfall produced lower peak discharges but exhibited a similar increasing trend. These findings indicate that even relatively small land cover changes can significantly affect flood discharge characteristics in the Serayu Watershed, highlighting the importance of land use management as part of flood mitigation and sustainable watershed management strategies.