Tehran is sinking

Decline in the groundwater level leads to significant subsidence

Average Lowering Rate in Greater Tehran from 2015 to 2017 © Haghshenas Haghighi and Motagh, 2018 (GFZ)
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Sinked down: The underground of the Iranian capital Tehran continues to sag. Drying groundwater basins have led to subsidence of several meters in some areas over the past 15 years. The affected areas partially lowered at speeds of over 25 centimeters per year. The consequences of this process are already clearly visible in many places, as researchers report.

Much of the drinking water worldwide comes from the groundwater. But this underground resource is finite: studies show that only six percent of groundwater resources regenerate regularly. In addition, already one third of the groundwater reservoirs is overused. As more and more water is extracted and at the same time the flow from rivers is often restricted by dams, the groundwater reservoirs are increasingly drying up.

Another problematic effect is associated with the drop in groundwater levels: where the levels are lower, the soil above the groundwater basins gradually lowers. In San Francisco, this phenomenon is now threatening even the international airport. Also in Tehran has been observed for some time a subsidence of the subsurface. The magnitude of this effect has now been investigated by Mahdi Motagh and Mahmud Haghshenas Haghighi from the German Geo Research Center (GFZ) in Potsdam.

Columns and cracks

For their study, the researchers evaluated data from four radar satellite systems from the years 2003 to 2017. Thanks to a special radar interferometry method, they were able to create an image of the topography of the earth's surface from the recorded radar signals. At what points in the Greater Tehran had there been any subsidence over time and how much had the earth there lowered?

The evaluations showed that over the course of the investigation period, three different areas have decreased in the region - considerably. According to this, the ground sank at speeds of more than 25 centimeters per year. Overall, the subsoil in the affected areas sank several meters. The consequences of this process are already clearly visible. The deformation of the underground has left gaps and cracks in many building walls, as the scientists report. display

Irreversibly damaged

The analyzes also revealed another fatal effect: Years of exploitation have irreversibly damaged groundwater basins in certain areas. According to the team, they will not be able to store as much water in the future as they used to. However, with well-founded plans for the water industry, the situation can be relaxed, says Motagh: "For sustainable development, science and research can help Iranian administrations and governments To revise their water management policies. "

In the future, he and his colleague will expand the area under investigation and survey the lowering of the country outside of Tehran using satellites. "Such data from cuts in large areas brings new challenges. We are currently developing software tools to analyze huge amounts of radar data, "concludes Haghshenas Haghighi. (Remote Sensing of Environment, 2018; in press)

Source: Helmholtz Center Potsdam GFZ German Research Center for Geosciences

- Daniel Albat