River Deltas Sinking Around the World

Published on September 30th, 2009 | by

Major river deltas around the world are sinking. A recent study published in the journal Nature Geoscience concluded that 24 of 33 major river deltas around the world are sinking.

Photo Credit: trexcaliNile River Delta
Nile River Delta

Deltas are formed when rivers deposit the sediment that moving water loosened and carried from the riverbed. Dams and water diversions mean that less sediment moves through the river- that means less sediment to maintain the deltas. Water taken from aquifers for drinking, industry and agriculture along with gas and oil extraction compacts the ground and makes it sink.

Beyond the environmental impact, it’s dangerous for anyone living near the deltas because of increased flood risk puts the close to half a billion people who live in river-delta regions at risk. According to the study, 85% of major river deltas have recently seen severe flooding- and it will get worse as deltas are sinking due to lack of sediment and sea levels rise from climate change.

Name a river and this is happening:

The Mississippi in the United States. The Colorado in Mexico. The Nile in Egypt. The Yangtze in China. The Ganges in India. The Rhone in France. The Po in Italy. The Chao Phraya in Thailand. The Sao Francisco in Brazil. The Tone in Japan.

All of these and more have been labeled high-risk due to evidence of “virtually no aggradation (supply of sediment) and/or very high accelerated compaction.”

“This study shows there are a host of human-induced factors that already cause deltas to sink much more rapidly than could be explained by sea level alone,” said co-author Albert Kettner of the University of Colorado in Boulder.

Researchers used NASA satellite images, historical records and other measurements to asses changes in the deltas over time. Researchers also found that the deltas are sinking much faster than could be attributed to natural causes or even climate change. The accelerated sinking is caused by human activity.

In addition, the data show that the deltas are sinking four times faster than any natural process might account for, according to geologist and co-author Irina Overeem of the University of Colorado, Boulder. She added: “we were struck both by the prevalence of this trend in deltas worldwide as well as by the rate.”

[Research from BBC, China Daily and Science Mag]

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