The importance of integrated solutions to flooding and water quality problems in the tropical megacity of Jakarta

Rapid urbanisation is transforming many urban rivers by affecting their hydraulic conditions and water quality. This process is particularly intense in some areas of the planet, where migratory phenomena and the associated urbanisation pace and conurbation are extreme. In these cases, the lack of water supply and sewerage infrastructures can lead to enormous pressure on urban river corridors, which often implies irreversible pollution of surface waters and shallow aquifers. In this article we address the problem of how integrated planning of urban river corridor management is essential to achieve sustainable solutions and how modern simulation tools can contribute to this effect. This is done by reporting about an exemplary case study, the Ciliwung River flowing through Jakarta, which is highly polluted and floods frequently large areas of the city. Indonesian authorities’ highest priority is to reduce the flood problem but without a clear integrated rehabilitation strategy that accounts for water quality issues. Through field campaigns and model simulations we demonstrate how measures to solve the flood problem can further deplete water quality if the pollution load is not reduced. Results suggest that the current hydraulic river regime produces a benefit for the river health by increasing oxygen levels, natural degradation processes and dilution. A reduction in the average discharge by means of dam construction, as currently considered by the authorities, is likely to increase contamination levels of surface water and shallow aquifer, which is recharged by the river.