Brett Walton wrote an article titled As Seas Rise, Unchecked Groundwater Use Sinks Coastal Cities.
« 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. »
« 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. »
« 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. »
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