The influence of aquatic buffer characteristic of Ciliwung River from the Katulampa Weir to Manggarai Water Gate on hydrograph characteristics of design flood

Increasing population in Jakarta leads to increased needs of settlements and their supporting facilities. To compensate, various methods are being undertaken, from utilization of open area to the riparian, especially in the Ciliwung River. This utilization results in the loss of riparian natural ability, which changes the river’s hydraulic condition. These riparian changes will significantly affect the roughness coefficient. The roughness coefficient is a value that is affected by channel irregularity, variation of cross-section, effects of obstructions, vegetation, and degree of meandering. Changes of the roughness coefficient will influence the velocity of the stream. The purpose of this research is to determine the effect of riparian characteristics to the roughness coefficient that affects the stream velocity, which has impact on the peak time of the hydrograph. The peak time shift can be seen in the flood hydrograph characteristics of the Ciliwung River from the Katulampa Weir to the Manggarai sluice gate. Identification of Ciliwung riparian conditions at that segment is conducted by river routing. HEC-RAS 4.1.0 [1] application is used to obtain a design flood hydrograph at Manggarai Water Gate. To know the influence of riparian characteristics to roughness coefficient, HEC-RAS 4.1.0 simulation is done using existing and natural condition to compare the hydrographs between those two conditions. It obtains a lower peak discharge and extended duration of the hydrograph