Tom Parsons, a geologist from the US Geological Survey agency, and researchers from the University of Rhode Island have been considering the role that the weight of New York City’s built environment might play in a process called ‘subsidence’. This term is used to refer to either natural or man-made changes in “downward elevation”.
The study suggests that parts of Manhattan Island could be sinking as quickly as Venice. The Italian tourist spot has sunk 15 centimetres in the last 100 years, according to the Castello Institute of Marine Sciences, and the acqua alta [spring tide floods] are not an uncommon occurrence. But could Times Square eventually resemble St Mark’s?
The process has a range of causes, including the interaction between water and soils, tectonic activity, mining and other human interventions.
The idea that coastal cities could be especially prone to subsidence, increasing the threat from projected sea level rises, has been well established. However, the researchers in this study look to the impacts and weight of the built urban environment, a cause not often considered as a contribution to subsidence.
The Empire State Building, once the city’s largest skyscraper, proudly proclaims its weight as 331,000 tonnes, with its structure using more than 1 million cubic metres of Indiana limestone. It’s not just Manhattan that is sinking under the weight of its skyline.
Within the study, the researchers calculate the mass of over a million buildings located within the five boroughs of New York City and model their potential contribution to subsidence across a variety of soil types. They found that ongoing urbanisation and the cumulative pressure of the buildings may exacerbate the sinking of the ground. The highly developed regions of Brooklyn and Queens are highlighted as areas where significant subsidence is occurring (though northern Staten Island is said to carry a less heavy load).
The researchers conclude by noting increased mass can exacerbate subsidence, which can imply a growing flood hazard in coastal cities. New York City, which has a population of 8.4 million, has already faced issues with flooding – floods following Hurricane Ida in 2021 saw the city move to a State of Emergency.
The researchers relay the study seeks to “raise awareness that every additional high-rise building constructed at coastal, river, or lakefront settings could contribute to future flood risk, and that mitigation strategies may need to be included”.
The source of this hardhatNEWS is NZHerald 
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