As Seas Rise, Unchecked Groundwater Use Sinks Coastal Cities

Life on the coast is already hazardous. Groundwater mismanagement amplifies other risks.

In Jakarta, sinking due to groundwater withdrawals and urban growth, lies Lake Pluit, which is below sea level. The district around the lake was inundated by historic flooding in 2007. Photo J. Carl Ganter/Circle of Blue

By Brett Walton, Circle of Blue

Joko Widodo, in a press conference on Monday, shook up Indonesian society.

Widodo, who was re-elected this spring to a second term as the county’s president, revealed his preferred site for a new capital city.

Jakarta, the current seat of power, will remain the center of business. But under Widodo’s proposal government offices will relocate to a new campus in the province of East Kalimantan, on the island of Borneo.

In most megacities, groundwater is a major driver of subsidence.” Gilles Erkens, Deltares

Widodo had hinted at the plan in April, and proponents justify the long-debated move for several reasons. Traffic in Jakarta, home to more than 10 million people, is unwieldy. There are equity issues: Java, the island on which Jakarta sits, is where political and economic power is concentrated. Then there are environmental factors: polluted air, sinking land, and, for the coastal metropolis, a mounting flood risk.

Certain districts of Jakarta, especially near Jakarta Bay, have sunk more than 4 meters since the 1970s, a direct result of excessive and uncontrolled groundwater use. Removing water from layers of soft soils causes the land to compact and settle, like a sponge being squeezed dry. It’s a process called subsidence, and it is jeopardizing the future of a number of coastal cities, especially in Asia: Ho Chi Minh, Hanoi, Semarang, Bangkok, Dhaka, and others.

“In most megacities, groundwater is a major driver of subsidence,” said Gilles Erkens, a subsidence expert at Deltares, a research group based in the Netherlands.

The coasts, particularly delta regions, were a natural setting for urbanization. At the intersection of river and ocean, they connected upstream producers to global markets. It was a successful model, for a time. But a new geography of risk has emerged. Because of climate change and mismanagement of natural resources, coastal cities are increasingly hazardous locations.

Subsidence is one of those risks. Shifting land topples buildings and buckles roads and bridges. It is worsened by unrestrained urbanization on fragile, compactable soils and by upstream dams that block the sediments that replenish delta lands. These sediments, which are also channeled out to sea by levee systems, are “the only natural compensation method available” for land lost to compaction, Erkens told Circle of Blue. And, by engineering design, it has been taken away.

These factors combine to amplify flooding risks from rising seas and storm surges, which are already calamitous. Along the sea wall in Jakarta, a pedestrian looks up, not down, at the waters of Jakarta Bay. Northern districts of the city, those adjacent to the bay, have the worse subsidence and highest flood risk.

In Surat, India, expected to be the world’s fastest-growing city in the next 15 years, some 2 million people, mostly slum-dwellers, could be living in high-risk flood zones by 2070 if subsidence and population growth trends continue, according to an International Institute for Environment and Development report. When the land sinks at the same time that the seas swell, flood disasters become more damaging.

Much of the subsidence that has already occurred is irreversible. But cities can stanch future declines by taking action now, Erkens said. That means restricting groundwater use and finding alternative supplies. Tokyo, which was plagued by high subsidence rates that dropped the city by as much as 4 meters in the early 20th century, built reservoirs and shifted to river water by the 1960s. In Texas, which faced a similar fate in the Houston metro area, the Legislature established a government agency in 1975 to regulate groundwater withdrawals in Harris and Galveston counties. Municipalities gradually shifted to river water from surface reservoirs. Subsidence in those areas has been halted or significantly slowed.

Bangkok today is a city in transition between a subsidence crisis and resolution, Erkens said. City officials instituted a tax on groundwater withdrawals in an attempt to reduce consumption.

These are not quick and easy fixes. Controlling subsidence requires scientific understanding of the interaction between groundwater and land, political will to enforce groundwater restrictions, project planning, and money to carry out the new infrastructure. Still, Erkens sees Tokyo, Houston, and Bangkok as hopeful examples for Jakarta and others.

“Once we get these stories told, other cities will be less reluctant to do something about it,” Erkens said. “It’s possible to take action and have a successful economy.” And, one might add, a capital where the land is stable, at least for a while longer.

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