Floods that occur in the Upper Citarum River Basin are generally caused by flood discharge that exceeds the capacity of the Citarum River. Dayeuhkolot is one of the areas that is often flooded in the Upper Citarum River Basin. The Citarum River Authority has made efforts to handle floods in Upper Citarum by constructing the Nanjung Tunnel. When floods occur, Nanjung Tunnel will function to divide the water partially into the tunnel and through the Curug Jompong. SOBEK Model was utilized to find out the effect of the Nanjung Tunnel against flood inundation in Dayeuhkolot. This flood modelling also accommodates other efforts that have been made by BBWS Citarum such as the Cieunteung Pond and Cisangkuy Floodway. A 20-year return period was used for modelling. From the results of the modelling, it was found that difference in flood inundation area with and without the Nanjung Tunnel was 12.5 Ha or 3.5 %, with the duration of the overall inundation being reduced by 4.9 hours. Nanjung Tunnel does not have a great influence on the area of inundation, but it has an effect on reducing the duration of floods that occur in Dayeuhkolot.

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