JAKARTA - The Geological Agency has recorded a number of major cities on the island of Java experiencing land subsidence with a rate of more than five centimeters per year, even if it occurs not only on the coast but also in highlands such as Bandung.
Head of the Center for Water, Soil and Geological Environment Management (PATGTL) of the Geological Agency, Agus Cahyono Adi said that the City of Bandung and more broadly the Bandung Raya area experienced a decrease in land surface of more than five centimeters per year due to various factors.
First, said Agus in Bandung, Sunday, the factor is the massive industry, but then there is also a reason for soft soil and young sediment or geological conditions, then massive urbanization, building loads, and excessive groundwater exploration.
"The decline in land surface is multi-factor. This Bandung area was formed from an ancient lake, so the sediment deposits are relatively more unstable than areas formed from stronger lava clots," he said.
Agus explained that a number of factors that caused the subsidence of the land could not all be overcome, especially those related to geology.
However, there are factors that can be overcome to minimize land subsidence, namely the cessation of groundwater use.
"Natural factors cannot be (controlled), what can be controlled is reducing the use of groundwater," he said.
Besides Bandung, other areas that experienced a decrease in land surface of more than five centimeters are North Jakarta, Semarang (Genuk, Tanjung Mas, and Kaligawe), then Sayung in Demak, the coast of Pekalongan, and Surabaya east and north.
Acting Head of the Geological Agency Lana Saria in her statement also said that the cause of the land subsidence was the geological condition, namely young-aged sediment or sediment and soft soil. Which then exacerbated was the excessive exploitation of groundwater, building loads, and massive urbanization.
When combined with the rise in sea level due to global warming, the land subsidence that occurs has the potential to give birth to the risk of permanent flooding and rob. Other impacts are infrastructure and building damage, as well as a decline in quality of life and the environment related to health and sanitation problems.
"As well as economic losses due to increased costs for repairing buildings and infrastructure in affected areas and the loss of land areas," said Lana.
He said that the impact of land subsidence or land subsidence is one of the threats of disasters that occur over a long time, but has a wide impact. Generally, it includes urban areas, industries, and dense settlements.
The subsidence that occurred in the coastal areas of the north of Java Island, based on monitoring by the Geological Agency, has made land such as Jakarta and Semarang parallel or even lower than the sea level or lost.
The change from land to permanent waters removes settlements and ponds from the land map.
"Flash floods spread in North Jakarta, Pekalongan Regency and City, Semarang City, and Demak Regency," said Lana.
The condition of the land subsidence can also be seen from changes in the coastline, the construction of sea dikes, and flood pumping activities.
However, for the Jakarta area, the Geological Agency stated that there was a subsidence of the land in the groundwater basin.
Based on global positioning system (GPS) measurements in the period 2015-2023, there was a decrease in land between 0.05 to 5.17 centimeters per year. The decrease in land surface in Jakarta has even been said to be relatively invisible since 2020 to the present.
Meanwhile, based on previous GPS measurements, in the period 1997-2005, the rate of land subsidence in Jakarta varied from 1-10 to 15-20 centimeters per year.
Meanwhile, according to a report by the World Economic Forum (WEF) published last November, some areas of Jakarta were recorded to have collapsed by up to 28 centimeters. Jakarta, as well as Semarang, is said to be sinking at a rate 10 to 20 times faster than the rise in sea level.
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