Analisis Debit Banjir Menggunakan Metode Alih Ragam Hujan-Limpasan. Studi Kasus: Daerah Aliran Sungai Kupang (Tengah), Nusa Tenggara Timur.

POELINGGOMANG, Martha Tessalonika (2025) Analisis Debit Banjir Menggunakan Metode Alih Ragam Hujan-Limpasan. Studi Kasus: Daerah Aliran Sungai Kupang (Tengah), Nusa Tenggara Timur. Undergraduate thesis, Universitas Katolik Widya Mandira Kupang.

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Abstract

Flooding is a recurring problem in Kupang City, particularly on Jalan Jenderal Soeharto, caused by high rainfall and inadequate river and drainage capacity to accommodate surface runoff. This study aims to analyze flood discharge in the Kupang (Central) River Basin using the rainfall-runoff method, as well as to evaluate the capacity of rivers and drainage channels at the study site. The research method involved collecting primary data through site surveys and secondary data in the form of rainfall data from the last 30 years from the BMKG, as well as land cover maps from BIG. The hydrological analysis involved data consistency testing, determining rainfall using frequency distributions (Normal, Log-Normal, Gumbel, Log- Pearson III), and calculating runoff coefficients. Hydrological analysis was conducted using data consistency tests, determination of design rainfall using frequency distributions (Normal, Log-Normal, Gumbel, Log-Pearson III), and calculation of runoff coefficients. Flood discharge simulations were performed using HEC-HMS software with the SCS-CN method, and river capacity analysis was conducted using the Manning formula. The simulation results show that the peak flood discharge calculated using HEC- HMS is 45.21 m³/s for a 1-year return period, 63.44 m³/s for a 2-year return period, and reaches 218.48 m³/s for a 100-year return period. All these values significantly exceed the maximum capacity of the river calculated using the Manning formula (43.83 m³/s). The 2D flood simulation using HEC-RAS also shows the potential for widespread flooding. This significant difference indicates that the river is unable to accommodate water flow during heavy rainfall, even at low return periods, posing a high risk of flooding and inundation in the surrounding area. However, this study has limitations in the number of rainfall stations analyzed (only one station), assumptions about runoff coefficients based on literature, and limitations in topographic data resolution, which may affect simulation accuracy. For future research, it is recommended to use rainfall data from multiple stations, direct measurements of hydrological parameters in the field, hydrodynamic modeling with higher spatial resolution, and studies of drainage improvement and river normalization scenarios to support more effective flood control planning.

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