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Indonesia and the Netherlands have kicked off the Water as Leverage program for Semarang, a rapidly subsiding and flooding port city on the island of Java home to 1.7 million inhabitants. Two design teams will look into the city’s water challenges and develop conceptual climate-adaptive and innovative solutions together with local stakeholders and turn them into bankable water infrastructure projects.
The program started on 3 and 4 September with the first of a series of design workshops. Partners that already collaborate in the Building with Nature programme in Demak district, adjacent to Semarang, are part of one of the design teams and help to expand knowledge on the watershed feeding Semarang.

Vicious circle

At a rate of sea level rise upward of 6 mm per year, and, in some places, a subsidence rate of over 10 cm per year, Semarang finds itself in a vicious circle where its water-related practices directly contribute to higher flood risk. In parallel, the city is rapidly expanding in areas that are at risk, with lack of effective governance to adapt to ever-changing environmental conditions.

Coastal flooding problems in Semarang and Demak are interrelated

Wetlands international, Deltares and Diponegoro University are all part of one of the two design teams: the ONE Resilient Team, led by design and urban planning firm One Architecture & Urbanism (ONE). These partners are already collaborating in Java in the Building with Nature Indonesia project located in Demak district, adjacent to Semarang. Coastal flooding problems in Semarang and Demak are interrelated. Coming from the experiences in the Demak project, partners have learned that they need to look at the entire watershed feeding Semarang. This is because enhanced surface water management in the watershed can help reduce the groundwater depletion that is contributing to subsidence and ultimately, in combination with sea level rise and erosion, in flooding.

Knowledge base

To expand the knowledge base of the surface water system, Deltares just released their report ‘Exploratory Integrated Water Resources Management (IWRM) Study in Demak Coastal Area: Water Availability and Water Users’. In the report, demands of several water user groups from the coastal community are evaluated against the surface water supply by the river network in Demak. Possibilities are explored for availability and sustainable use of surface water in the area.

Sustainable water management can help prevent flooding

The Deltares modelling study shows that the annual water supply from the rivers is abundant in Demak, however it is unequally distributed over space and time. The watershed has a surplus of water over the wet season and this surplus is not retained and used efficiently during the drier periods. Furthermore, most of the available river water is used in Eastern part of the province. Sustainable freshwater management and distribution is key to minimise groundwater pumping and subsidence. Since subsidence threatens long-term survival of mangrove forests, preventing this phenomenon also helps to maintain a healthy mangrove forest, which is important for coastal protection and aquaculture.