Central Jakarta is developed on a natural flood plain with a long history of flooding that leads to a series of flood control systems with Manggarai Gate at its center. Nowadays, as a regulator gate, Manggarai Gate is still good enough to control flood hazards in Central Jakarta. However, after operating for more than 100 years, it is necessary to measure the influence of increasing seismic activity, maximum rainfall, sedimentation rate, and solid waste problems on the potential of the Manggarai Gate breach. This study was made to identify flood hazards generated by the Manggarai Gate breach. An overtopping flow generated by excessive runoff is encountered as the gate breach mechanism. A mathematical model using HEC RAS to predict flood inundation due to the breach of Manggarai Gate in that area is presented in this paper. Due to the gate breach, the flood propagation was calibrated upon field observation data. The simulations were done for Q100 (692.6 m 3 /s) with no breach mechanism; and Q100 with a breach mechanism. Based on that flood simulation, it is found that the flood inundated area for the gate breach scheme is approximately 259% compared to the scheme with no gate breach. Meanwhile, the hazard index for the gate breach scheme becomes 225% for the low level, 249% for the medium level, and 276% for the high level. Further study is needed to identify a proper measure to minimize gate breach-induced flood hazards.