Nature-based solutions for integrating flood and land subsidence: A case study in Jakarta and Semarang

Floods in Jakarta and Semarang are more frequent and impact more expansive areas. So far, flood management has been done mainly by increasing the capacity of drainage channels and draining water into the sea more quickly. This flood management needs to be evaluated because it leads land subsidence in Jakarta and Semarang to deepen. Thus, this research aims to identify the extent to which land subsidence causes the expansion of floods and alternative solutions to deal with floods and land subsidence in an integrative manner, especially in Ciliwung (Jakarta) and Garang (Semarang) watersheds. The method used was a review of various publications concerning findings of land subsidence, flooding, and the experiences of several countries in dealing with these problems. The results showed that land subsidence has occurred in Jakarta and Semarang. As a result of land subsidence, the flooding areas have increased due to the increase in lowlands, and therefore, it is difficult for the existing water to flow into the sea. Handling floods and land subsidence cannot be conducted locally but must be carried out in an integrative manner with a watershed and groundwater basin approach. One of the causes of land subsidence is excessive groundwater extraction. On the other hand, the groundwater must be increased. The increase in groundwater supplies not only reduces land subsidence but also reduces flooding, seawater intrusion and prevents drought in the dry season. A nature-based solution for reducing flood and land subsidence can be achieved by increasing vegetation cover and constructing water conservation buildings in the upstream areas.