Numerical Simulation Of Hydrodynamics In Jakarta Bay With Giant Sea Wall

The construction of Giant Sea Wall(GSW)in Jakarta Bay is potentially proposed in Master Plan for National Capital Integrated Coastal Development(NCICD).The seawall aims to provide a solution to protect Jakarta against the flood and addresses other environmental problems;however,this construction might also sufficiently change the hydrodynamics in the area of Jakarta Bay.This research is to investigate the impacts of the seawall in Jakarta Bay by using a validated numerical model.This study applies a high-resolution unstructured mesh to identify the complicated coastal-line,islands,rivers,and the sea wall construction.The numerical model uses bathymetry data which is obtained from nautical charts of Jakarta Bay and combined with survey data.The model is forced by 8 tidal constituents at the lateral boundaries and also considers river discharge and wind data in the period of August to September in 2015.Observational data from two sites are used to validate the performance of the model.Simulated tidal elevations and currents agree well with observation data,as indicated by the statistical skill parameter larger than 0.86.The main outcomes from this study can be summarized as follows:1)The numerical result shows the maximum tidal range at location inside the reservoir is slightly increased from 0.72 m to 0.78 m in the open gates scenario,and from 0.74 m to 0.79 m at the location outside the reservoir.In the close gates scenario,the water level in the reservoir is significantly increased to 1.56 m due to the fill of river discharge during 24 day’s simulation.The model results demonstrate that the present Jakarta Bay is dominated by zonal flow component(east-west),which current is about 0.18 m/s in the eastern of the bay,0.12 m/s in the center and 0.06 m/s in the nearshore region.2)The construction may create a high speed current at the gate,with the peak velocities about 0.56 m/s and 0.48 m/s at the west and east gate,respectively,in the open gates scenario.The alongshore currents with a speed of 0.23 m/s near the wings of the wall are also predicted by the model.The simulated surface residual current flows from the east to the west,corresponding to the wind direction during the simulation.At the surface layer,the highest residual current with a magnitude of～0.05 m/s might be occurred in the center of the bay,in the existing scenario.However,the residual current in the west gate increases up to 0.08 m/s,and in the reservoir it vary from 0.01 to 0.03 m/s,in the open gates scenario.3)The model results show in the center of Jakarta Bay,the salinity is about 30-30.5 PSU and 31-31.5 PSU,at the surface and bottom layer,respectively.The construction of GSW might reduce the salinity in the reservoir up to 2.5-5.4 PSU at the surface,while about 1.5-4.6 PSU at the bottom layer,in the open gates scenario.Meanwhile,the salinity decreases about 0.31 PSU and 0.19 PSU per day,at the surface and bottom layer,respectively,in the close gates scenario.This study provides a first-trial to quantitatively evaluate the impacts of GSW on the tides,currents,salinity in Jakarta bay,which can make an important contribution to the development of this project and provide useful information for further study in water quality and the related problems caused by GSW.