Flood Control Reduction Analysis using HEC-RAS due to Local Floods in Central Jakarta

Abstract

There are two types of floods in Jakarta: upstream flooding and local flooding. In general, floods in DKI Jakarta are caused by local floods. The main cause of this flood is the occurrence of high rainfall, poor drainage system, and land subsidence. This study will analyse the local flood that occurred in Gunung Sahari, Central Jakarta. Judging from the existing conditions, sedimentation occurs in the drainage channels. This sedimentation causes a reduction in the existing channel capacity. Based on a hydrological and channel capacity analysis, the existing drainage channels are designed based on annual rainfall i.e. return period 1-2 years, which is 133.10 mm/day. Flood modelling is done for existing conditions. Based on the results of modelling, floods that occur in locations between 50 cm - 100 cm. Due to dense housing conditions, widening and normalizing the channel is difficult. Therefore, flood reduction will be assisted by pumps. The pump will be installed in the downstream of the main drain, which is connected to Mati River. This pump is designed with a capacity of 0.5 m3 / sec. Based on the results of modelling, with a largest pump capacity of 0.5 m3/sec, flooding is only reduced by 5 cm - 7 cm. Due to the lack of effectiveness of the pump, retention ponds will be designed to reduce surface runoff. Retention ponds are designed with an area of 1 ha and a depth of 1.5 m. Modelling is done in the presence of a retention pond. With the addition of retention ponds, annual flooding for the 2-year return period on Gunung Sahari could be reduced. Therefore, the discharge that will be received by the drainage channel will be smaller than the capacity of the channel itself and the flood will be completely reduced.