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Communities of Southern Chesapeake Bay Find Sea Level Rise Heightened by Sinking Land



Communities of Southern Chesapeake Bay Find Sea Level Rise Heightened by Sinking Land

Communities and coastal habitats in the southern Chesapeake Bay region face increased flooding because, as seawater levels are rising in the bay, the land surface is also sinking._ A new USGS report released today concludes that intensive groundwater withdrawals are a major cause of the sinking land, or ‘land subsidence’, that contributes to flooding risks in the region. 

“From a practical viewpoint, sea level is relative to the land surface,” said Jerad Bales, Acting Associate Director for Water at USGS.  “Whether the water is rising or the land is sinking, or both, the effect is the same:  greater vulnerability to coastal storms and loss of important coastal habitat, both of which result in economic losses.” 

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 r 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.) Land subsidence alone causes more than half of the observed relative sea-level rise in the southern Chesapeake Bay.

While there are several factors influencing land subsidence, aquifer system compaction, caused by extensive groundwater pumping in the Virginia Coastal Plain, is a major cause in the Norfolk area. Land subsidence has occurred around Norfolk at an average rate of 3 mm/year since 1940. 

Low-lying communities and critical habitats  in the Chesapeake Bay region are especially vulnerable to damage from the relative sea-level rise caused by land subsidence. Communities in the southern Bay can experience increased flooding. The loss of coastal marsh and wetlands decreases the extent of specific habitat that waterfowl need to winter in the Bay region.

The report suggests that changing groundwater management practices could slow or mitigate land subsidence and relative sea-level rise.  Moving groundwater pumping away from high-risk areas or decreasing groundwater withdrawal rates can reduce subsidence in low-lying areas prone to flooding. These results will be used by federal and state managers to consider adaptation strategies in their efforts to restore and protect the Chesapeake Bay.

Continued monitoring, mapping, and modeling are scientific tools needed to help natural resource managers and urban planners understand and reduce or mitigate land subsidence. 

Changing resource management practices in response to rising seas and sinking land will require sustained public commitment.

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

Learn More

Land subsidence and over-withdrawal of groundwater from aquifers are two critical topics currently being addressed by the USGS Cooperative Water Program and the USGS Groundwater Resources Program.

Science summary of sea-level rise in the Chesapeake Bay  (May 2013)

Sea Level Rise Accelerating in U.S. Atlantic Coast  (USGS release, 6/24/2012) 

USGS Newsroom



More information

Parameter Value Description
Magnitude mb The magnitude for the event.
Longitude ° East Decimal degrees longitude. Negative values for western longitudes.
Latitude ° North Decimal degrees latitude. Negative values for southern latitudes.
Depth km Depth of the event in kilometers.
Place Textual description of named geographic region near to the event. This may be a city name, or a Flinn-Engdahl Region name.
Time 1970-01-01 00:00:00 Time when the event occurred. UTC/GMT
Updated 1970-01-01 00:00:00 Time when the event was most recently updated. UTC/GMT
Timezone offset Timezone offset from UTC in minutes at the event epicenter.
Felt The total number of felt reports
CDI The maximum reported intensity for the event.
MMI The maximum estimated instrumental intensity for the event.
Alert Level The alert level from the PAGER earthquake impact scale. Green, Yellow, Orange or Red.
Review Status Indicates whether the event has been reviewed by a human.
Tsunami This flag is set to "1" for large events in oceanic regions and "0" otherwise. The existence or value of this flag does not indicate if a tsunami actually did or will exist.
SIG A number describing how significant the event is. Larger numbers indicate a more significant event.
Network The ID of a data contributor. Identifies the network considered to be the preferred source of information for this event.
Sources A comma-separated list of network contributors.
Number of Stations Used The total number of Number of seismic stations which reported P- and S-arrival times for this earthquake.
Horizontal Distance Horizontal distance from the epicenter to the nearest station (in degrees).
Root Mean Square sec The root-mean-square (RMS) travel time residual, in sec, using all weights.
Azimuthal Gap The largest azimuthal gap between azimuthally adjacent stations (in degrees).
Magnitude Type The method or algorithm used to calculate the preferred magnitude for the event.
Event Type Type of seismic event.
Event ID Id of event.
Event Code An identifying code assigned by, and unique from, the corresponding source for the event.
Event IDS A comma-separated list of event ids that are associated to an event.

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