Rainfall-Runoff modelling on Ngotok watershed with sub-catchment area

Flood problems commonly occur at Mojokerto, East Java Area. Generally, flood problems by not proper drainage systems, and the most influential factor are the damage of the catchment area. The result of land use changing at river basin is the occurrence of unpredictable discharge on it. This research was conducted in the Ngotok watershed using HEC HMS software. The data will be transformed to daily discharge which uses some parameters, such as sub-catchment area, infiltration, evaporation, Manning's friction coefficient, and the land slope. The aim of this study was to determine: (1) formation of the sub-watersheds in accordance with the conditions of the Ngotok watershed (2) the average rainfall in each of the Ngotok watersheds (3) the results of the modeling of the transformation of the Ngotok watershed rain discharge (4) model reliability. From the modeling results obtained hydrograph with a peak discharge of 2-year return period of 246.9 m3/s, a 5-year return period of 350.7 m3/s, a 25-year, and return period of 476.2 m3/s, and a 50-year return period of 523 m3/s. Calibration using the Nash formula obtained an EI value of 0.89, which means the modeling results are in the category of high accuracy.