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cientists from reputable universities and Dutch consultant Deltares have offered a cheaper alternative to the proposal to mitigate tidal flooding in subsiding Jakarta by building a seawall, called the Great Garuda, to close off Jakarta Bay and costing Indonesia US$20.3 billion in public-private partnerships over 15 years.

President Joko “Jokowi” Widodo has instructed his administration to continue with the seawall project, also called the National Capital Integrated Coastal Development (NCICD) project. He believes that the Great Garuda is the answer to Jakarta’s subsidence problem. “The development of the north coast of Jakarta, the NCICD, which was proposed a long time ago, is the answer for Jakarta,” Jokowi said in April, about a week after visiting the European Union, including the Netherlands.

Along with the NCICD, the central government says the controversial project of creating 17 artificial islets is to be continued as one package. A bribery scandal has rocked the 17-islet project and the central government has found several regulation violations in land reclamation by two giant property developers: Agung Sedayu and Agung Podomoro.

Scientists, however, say enclosing Jakarta Bay is not the answer to land subsidence, because even with a seawall, Jakarta would continue to sink. They say the solution to land subsidence is to stop groundwater extraction and limit construction in several fast — sinking areas, such as North Jakarta, or to use construction technology that would not put as much pressure on the land.

The president of the Indonesian Association of Urban and Regional Planners (IAP), Bernardus Djonoputro, said “the idea of the Great Garuda is falling from the sky” because several logical steps had been skipped before a decision was made on it.

The Bandung Institute of Technology’s (ITB) Muslim Muin, who earned his doctorate in ocean engineering from the University of Rhode Island, said the Netherlands and St. Petersburg in Russia needed giant seawalls for protection against storm surges, a threat from a body of water. “But in Jakarta, the threat is more serious. It’s from the land, from land subsidence, not from the rising sea level,” he said during a focus group discussion at the Goethe Institute in Central Jakarta recently.

NCICD data show that Jakarta is sinking at an average of 7.5 to 10 centimeters per year, with maximum subsidence in some areas recorded at almost 18 cm. NCICD data show that over the next 20 years, Jakarta will subside by up to 50 cm more, and the Great Garuda is therefore considered urgent.

Muslim pointed out several concerns about building a giant seawall, including the maintenance of a powerful pump with a capacity of 730 cubic meters of water per second needed for the Great Garuda. He said based on his calculation of water volume from Jakarta’s 13 rivers, the Great Garuda would need a more powerful pump with a capacity of up to 1,100 cubic meters per second. Currently, the most powerful pump in the world has a capacity of 600 cubic meters per second.

“Improving existing seawalls along the northern coast would be enough. Building a giant seawall would be a big mistake. The operational costs would be huge,” he said.

The NCICD master plan shows that operational and maintenance costs for the Great Garuda system would reach $69 million per year.

Improvement of existing seawalls is required in the NCICD, which is in Phase A called a “no regret policy”.

One of the Dutch consulting institutes that made the NCICD master plan, Deltares, has written a report titled “Sinking cities: An integrated approach towards solutions”, which discusses places that are sinking faster than the sea level is rising: Jakarta, Bangkok, Ho Chi Minh City, Tokyo, Manila and west Netherlands. The more than 5,000 word report uploaded on deltares.nl does not mention the word “seawall”, not even once.

It proposes 10 key issues and possible solutions, and again, not one of them mentions seawall, giant or otherwise. It does mentions restriction of groundwater extraction, natural and artificial recharge of aquifers, integrated (urban) flood water management (which does not include any walls) and the integration of geotechnical aspects in the planning and designing of buildings and infrastructure.

Alan Koropitan of the Bogor Institute of Agriculture (IPB) said that instead of closing off Jakarta Bay with the Great Garuda and building artificial islets, Jakarta should focus on cleaning up its heavily polluted rivers. “It will be a difficult task, but when it is accomplished it will be a source of national pride,” said Alan, who earned his PhD from Hokkaido University in oceanography.

Clean river water will provide a supply of raw water to increase the coverage of tap water companies in Jakarta to 100 percent and allow for a restriction on groundwater extraction. Current tap water coverage remains at about 60 percent, caused by a lack of raw water supply from Jatiluhur Dam in West Java and the Tangerang water company, among other things.

Deltares’ paper also shows that Tokyo stopped its subsidence by restricting groundwater extraction in the early 1960s and the sinking decreased in about 10 years to close to zero.

Jan Jaap Brinkman of Deltares told The Jakarta Post in an email interview in October last year that, “The cheapest and most easy solution is stop the sinking. The only thing Jakarta needs to do is to stop the deep groundwater use and the sinking will stop within five to 10 years. Then you will not need a closed Jakarta Bay, you will not need a giant seawall. Of course, you could still improve the harbor and have better coastal development, but Jakarta Bay does not need to be closed.”