Evaluation of Urban Polder Drainage System performance in Jakarta. Case Study Kelapa gading Area

Kelapa Gading area is located in the plains of North Jakarta about 6 km from the coastline of Jakarta Bay. Kelapa Gading area covers 1288 ha it consists of three large compartments and next to that the Kodamar Unit separated system from Kelapa Gading excess water of the area is discharged to Sunter river and Pertukangan River. The area is regularly flooded, especially during the wet season. Kelapa Gading area is in particular facing flood problem since Jakarta __ the capital city of Indonesia __ became the primary growth machine of the nation. Among others, this has resulted in suburbanization in Jakarta’s neighbouring regions. Land subsidence, which occurs due to huge groundwater extraction, and climate change are also contributing to flooding problem due to hydrologic changes that alter the magnitude and frequency of peak flows and sea level rise. Four main objectives are the basis for this research. First is describing the existing urban drainage and flood protection systems in Kelapa Gading area and other satellite cities (JABODETABEK). Second is analysing the possible impacts of land subsidence and sea level rise on inundated area. Next are some measures that would have to be taken into consideration in order to reduce the flooded area and provide adequate urban drainage and flood protection especially when the impacts of land subsidence and sea level rise are taken into account. The structural measures were studied by considering hydrologic and hydraulic conditions and by carrying out hydrodynamic modelling (DUFLOW) as tools for decision support which may evaluate options in developing urban drainage and flood protection scenarios for Kelapa Gading area based on a design rainfall with a chance of occurrence of 4% per year or the return period of 25 years. Scenarios on the improvement of the macro urban drainage system and the selected river basin were developed as follows: Scenario 1. The existing urban drainage was considered as one system with the sedimentation in the urban canal system. This represents the existing condition and has been used as the basic case; Scenario 2. Similar with the first scenario 1 but the designed urban canal profiles are used; Scenario 3. Each compartment is considered as a single polder; Scenario 4. To analyse the effect of land subsidence and sea level rise. In this case 1.25 m of land subsidence and 0.15 m of sea level rise will be considered for the 25 years time interval; The results indicate that due to lower topographic conditions in adjacent area caused by land subsidence and sea level rise, a combine system consisting of gravity drainage and pumping are primed to meet the future conditions of drainage system and flood protection in the future in Kelapa Gading area. Therefore an urban polder with its properties is proposed to be constructed.