Southern Chesapeake Bay Experiencing Land Subsidence (Sinking Land)

Communities and coastal habitats in the southern Chesapeake Bay region could face increased flooding because, as seawater levels are rising in the bay, the land surface is also sinking, according to a new USGS report.

The report cites intensive groundwater withdrawals as a major cause of the sinking land, or ‘land subsidence’, that contributes to flooding risks in the region.

The new study presents a variety of data and findings from previous studies to examine land subsidence in the southern Chesapeake Bay region.

Previous USGS studies have established that the Chesapeake Bay region has the highest rates of relative sea-level rise on the East Coast. The sea-level rise rates around the Chesapeake Bay range from 3.2 to 4.7mm/per year with 4.4 mm/yr in Norfolk. (A penny is about 1 mm thick.)

USGS estimates that land subsidence alone causes more than half of the observed relative sea-level rise in the southern Chesapeake Bay. Land subsidence has occurred around Norfolk at an average rate of 3 mm/year since 1940.

The study concludes that while several factors are influencing land subsidence, aquifer system compaction, caused by extensive groundwater pumping in the Virginia Coastal Plain, is a major cause in the Norfolk area.

The report suggests that changing groundwater management practices could slow or mitigate land subsidence and relative sea-level rise.

The study was conducted by the USGS Virginia Water Science Center and the Office of Groundwater. The study circular is available online.

source: U.S. Geological Survey

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