Flood Discharge Modeling in Krueng Langsa Watershed: Comparing Nakayasu and SCS-CN Methods for Risk Mitigation Eka Mutia (a*), Ellida Novita Lydia (a), Ika Adelia Winata (a), Nurul Fadhillah Siregar (a)
a) Department of Civil Engineering, Faculty of Science and Technology, Universitas Samudra, Langsa, 24416, Indonesia
Abstract
Flood discharge modeling is crucial for disaster risk mitigation, as floods account for 40% of natural disasters globally, causing USD 82 billion in annual losses. In Indonesia, frequent floods, especially in high rainfall areas like Aceh, exacerbate the risk. Langsa City, located on the eastern coast of Sumatra, regularly experiences flooding, especially in the Krueng Langsa Watershed, which receives an annual rainfall of 2300 mm. Poor water resource management, along with environmental degradation, exacerbates the flood risk in this region. This study aims to model flood discharge in the Krueng Langsa Watershed using two hydrological methods: the Nakayasu Synthetic Unit Hydrograph and the Soil Conservation Service Curve Number method. A comparison between these two methods was conducted to assess their accuracy in predicting flood discharge for various return periods. The methodology involved collecting rainfall data from local stations and estimating missing data using the Normal Ratio Method. Data consistency was tested using the double mass curve method. The Hydrologic Modeling System software was used to simulate runoff using both the Nakayasu and SCS CN methods. The results showed that the Nakayasu method provides more accurate flood discharge predictions, with an estimated peak discharge of 135 m3/s for a 25 year return period. In contrast, the SCS CN method proved less reliable under high-rainfall conditions. Therefore, the Nakayasu method, combined with HEC HMS simulations, is considered more reliable for flood management planning and infrastructure development in the Krueng Langsa Watershed.
