STUDY ON THE EFFECT OF CHANGES IN THE DISTRIBUTION OF RAIN ON THE LAST 5 YEARS OF JAKARTA FLOODS BASED ON THE 2D HEC-RAS MODEL

• Main Author: Saputra, Deri
• Format: Theses
• Language: Indonesia
• Online Access: https://digilib.itb.ac.id/gdl/view/49413
• Institution: Institut Teknologi Bandung

As Indonesia's capital city, Jakarta is one of the coastal areas with very high population growth. Floods in Jakarta occur almost every year due to inadequate flood control systems, low drainage systems, and garbage clogging drainage. Apart from population growth and land use, changes in rainfall characteristics also affect river flows. This study aims to obtain an overview of the parameters that influence the occurrence of flooding in Jakarta, especially during the last five years, and to obtain a flood hazard map that can be used as a reference in making a flood risk map as a disaster mitigation effort. Flood events were analyzed based on information obtained from 2014 to 2020. Based on secondary data, it can be concluded that some structural flood mitigation has not been able to reduce the risk of flooding in recent years significantly. Improved flood early warning systems can significantly contribute to reducing flood risk. This study examines the floods' characteristics in the Ciliwung River section of M.T Haryono to Manggarai Water Gate. In this study, HEC-RAS 1D / 2D simulations were carried out for floods that occurred in 2007, 2015, 2020, and 2, 5, 10, 25, 50, and 100 years of recurring floods. Based on the results of this study, it was found that the relationship between daily rainfall and the maximum discharge of flood events has a correlation value (R) of 0.567, so it can be interpreted that the correlation value is significant, and there is a correlation between rainfall and discharge. Looking at the flood records that have occurred, at the same time, there is a massive discharge value, but the value of rain that has occurred is small and vice versa. Possibilities that have occurred include undetected local rain and flood discharge that did not occur at the time of recording, or it could be due to the presence of garbage in the Ciliwung River. In the case of flooding in Jakarta in early 2020, the rain that occurred in the upper watershed raised the water level in Manggarai to + 7 m, and when accompanied by local rain in Jakarta, it could raise the water level by + 9 m. If you look at the travel time of the flood from the upstream, then the water from Katulampa Dam is estimated to arrive in Depok in about 3-4 hours, and the water journey from Depok to Manggarai ranges from 10-13 hours depending on the conditions of the water level downstream. Based on the simulation results that have been carried out, the Manggarai Sluice Gate's additional capacity does not significantly affect the floods that occur without the addition of the capacity of the Ciliwung River. Based on the flood hazard map analysis, it can be seen that flooding will continue to occur in the areas of Kampung Melayu, Manggarai, and Kebon Manggis. For the 100 year return period, the inundation extends to Bidara Cina, Kebon Baru, and Bukit Duri, but is still in the criteria of moderate danger. Normalization is a form of flood control in Jakarta, and since 2015-2017, the Ciliwung River's normalization activities have been carried out, but it stopped in 2017. Based on a study of Q2007, the normalized Ciliwung River flood water level can decrease by about 0,87 - 3 m compared to before normalization. If normalization is resumed, the flood water level may decrease by 0,1 – 1,23 m. From the simulation results, it can be concluded that rainfall with a magnitude of less than 45 mm does not cause flooding in the study area, and if you look at the existing conditions in 2020, it is necessary to complete normalization activities. The purpose of normalization is to minimize flooding due to the overflow of the Ciliwung River. In addition to normalization, it is also necessary to make embankments as high as 1,6 m, especially in the area of Kampung Melayu to Manggarai because the area conditions are lower than the river, which allows water to overflow into the settlements.