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The Application of ITS-2 Model for Flood Hydrograph Simulation in Large-Size Rainforest Watershed, Indonesia

Nowadays, the increasing intensity of extreme rainfall and changes in land use have triggered massive floods in various regions of Indonesia. The changes in the characteristics of these two parameters cause an increase in the peak and duration of the flood over time. Peak and duration of flood estimation might be very useful for the national and local government because it is closely related to the effectiveness of prevention and mitigation plan in the future. A hydrograph-based model constitutes one approach to estimating them simultaneously. The objective of this research is to examine the application of ITS-2 – a synthetic unit hydrograph (SUH) model which was developed at Sepuluh Nopember Institute of Technology (ITS) in 2017 – for estimating the peak flood discharge as a basis for planning disaster mitigation programs. This study was carried out by testing the reliability of the ITS-2 Model using the Nash-Sutcliffe Efficiency (NSE) indicator by comparing the measured unit hydrograph and synthetic unit hydrograph derived using the model, optimizing the parameters of the model, and then analyzing the transformation of rainfall-flood discharge in the Gumbasa Watershed, one of the major watersheds in Central Sulawesi Province, Indonesia. This catchment is part of the Palu watershed, which is largely a tropical rainforest conservation area known as the Lore Lindu National Park. The input model is based on the design rainfall with a certain return period using the frequency analysis where the data was obtained from the rainfall stations in the study area. The results of the research showed that the performance of the ITS-2 model was still very good with the NSE above 80%. The difference in the peak discharge of these two unit hydrographs is relatively low, with a deviation below 10%. The optimal values of the ITS-2 Model parameter coefficients consisting of C1, C2, and C3 were achieved at 1.29, 0.33 and 1.88, respectively. The results of the hydrograph analysis based on a 1-year to 100-year return period indicate that peak flood discharge ranges from 100 m3/sec to 550 m3/sec. From a series of analyses and tests that have been conducted in the previous and current research, it can be concluded that the ITS-2 Model can be applied to various watershed sizes, especially in Indonesia.