Prepared in cooperation with the 

Hampton Roads Planning District Commission

Land Subsidence and Relative 

Sea-Level Rise in the Southern 

Chesapeake Bay Region

Circular 1392

U.S. Department of the Interior

U.S. Geological Survey
Cover: Photographs, top left, the constructed colonial-era fort wall in Jamestown, Virginia, next to the James River, photograph by 

Barbara Lombardi, courtesy of The Colonial Williamsburg Foundation; top right, a great egret takes to the air along the Lynnhaven 

River in Virginia Beach, photograph by L. Todd Spencer, The Virginian-Pilot, July 2010, used with permission; bottom, Fort 

Monroe in Hampton, Virginia, photograph by Stephen N. Katz, The Virginian-Pilot, May 2005, used with permission.
Land Subsidence and Relative 

Sea-Level Rise in the Southern 

Chesapeake Bay Region

By Jack Eggleston and Jason Pope

Prepared in cooperation with the Hampton Roads Planning District Commission

Circular 1392

U.S. Department of the Interior

U.S. Geological Survey
U.S. Department of the Interior

SALLY JEWELL, Secretary

U.S. Geological Survey

Suzette M. Kimball, Acting Director

U.S. Geological Survey, Reston, Virginia: 2013

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Suggested citation:

Eggleston, Jack, and Pope, Jason, 2013, Land subsidence and relative sea-level rise in the southern Chesapeake Bay 

region: U.S. Geological Survey Circular 1392, 30 p., http://dx.doi.org/10.3133/cir1392.

ISSN 1067-084X (print)

ISSN 2330-5703 (online)

ISBN 978-1-4113-3716-9

Library of Congress Cataloging-in-Publication Data

Eggleston, Jack.

Land subsidence and relative sea-level rise in the southern Chesapeake Bay region / by Jack Eggleston and Jason Pope ; prepared in 

cooperation with the Hampton Roads Planning District Commission.

 pages cm. -- (Circular; 1392)

 Includes bibliographical references.

 ISBN 978-1-4113-3716-9 (alk. paper)

1. Hydrogeology--Chesapeake Bay Region (Md. and Va.) 2. Subsidences (Earth movements)--Chesapeake Bay Region (Md. and Va.) 3. 

Sea level--Chesapeake Bay Region (Md. and Va.) 4. Groundwater--Chesapeake Bay Region (Md. and Va.) 5. Flood control--Chesapeake 

Bay Region (Md. and Va.) I. Pope, Jason P. II. Hampton Roads Planning District Commission (Va.) III. Title.

 GB1016.6.E34 2014

 551.4909163’47--dc23

 2013048265
 iii

Contents

Description of Land Subsidence .................................................................................................................4

Why Land Subsidence is a Concern in the Southern Chesapeake Bay Region .................................4

Land Subsidence Contributes to Relative Sea-Level Rise.............................................................4

Land Subsidence Increases Flood Risk ............................................................................................5

Land Subsidence Can Damage Wetland and Coastal Marsh Ecosystems.................................6

Land Subsidence Can Damage Infrastructure ................................................................................6

How Land Subsidence is Measured...........................................................................................................7

Borehole Extensometers .....................................................................................................................7

Tidal Stations .........................................................................................................................................9

Geodetic Surveying ..............................................................................................................................9

InSAR ....................................................................................................................................................10

Causes of Land Subsidence.......................................................................................................................10

Aquifer-System Compaction From Groundwater Withdrawals ..................................................11

Glacial Isostatic Adjustment.............................................................................................................14

Other Causes of Land Subsidence...................................................................................................14

Rates of Land Subsidence and Sea-Level Rise in the Southern Chesapeake Bay Region.............15

Measured Rates of Land Subsidence .............................................................................................15

Rates of Sea-Level Rise.....................................................................................................................18

Links Between Groundwater Withdrawals and Land Subsidence ............................................19

What Resource Managers Should Know About Land Subsidence in the 

Southern Chesapeake Bay Region..............................................................................................20

Planning for Increased Flood Risks .................................................................................................20

Preventing Land Subsidence............................................................................................................20

Information Needed to Understand Land Subsidence and Sea-Level Rise .............................21

Need for Improved Understanding of Land Subsidence in the Region .....................................21

References Cited..........................................................................................................................................22

Figures

1. Photograph showing coastal flooding along the shore of the Elizabeth River in the

Ghent neighborhood of Norfolk, Virginia, from a minor tide in February 2003 ...................2

2. Map showing stations for monitoring land and sea elevations in the southern

Chesapeake Bay region...............................................................................................................3

3. Diagram showing shoreline retreat caused by a combination of sea-level rise and

land subsidence............................................................................................................................4

4. Photograph of Jamestown, Virginia, next to the James River showing the

reconstructed colonial-era fort wall .........................................................................................5

5. Photograph of downtown Franklin, Virginia, during flooding caused by Hurricane

Floyd in September 1999..............................................................................................................5

6. Diagram of forces and processes that influence marsh and wetland development. ......6

7. Photographs of the borehole extensometer in Franklin, Virginia.........................................7

8. Diagram of the borehole extensometer in Franklin, Virginia.................................................8

9. Map showing groundwater water-level decreases from 1900 to 2008 .............................12

10. Diagram showing aquifer-system compaction caused by groundwater withdrawals...13
iv 

11. Generalized hydrogeologic section illustrating layering in the Virginia Coastal Plain

aquifer system from west to east.............................................................................................13

12. Map showing land elevation change rates from 1940 through 1971 .................................16

13. Graph showing aquifer-system compaction measured by borehole extensometers

in Franklin, Virginia and in Suffolk, Virginia............................................................................17

14. Graph showing monthly mean sea levels at Sewells Point in Norfolk, Virginia, at

National Oceanic and Atmospheric Administration station................................................18

15. Graph showing groundwater withdrawal rates from Virginia Coastal Plain aquifers

from 1900 to 2008.........................................................................................................................19

16. Graph showing water levels in the Potomac aquifer at U.S. Geological Survey

(USGS) groundwater monitoring well in New Kent County, Virginia .................................19

Tables

1. Land subsidence monitoring methods......................................................................................7

2. Relative sea-level rise at selected National Oceanic and Atmospheric

Administration tidal stations in the southern Chesapeake Bay region ...............................9

3. Observed sea-level rise and subsidence in the southern Chesapeake Bay region .......17

Conversion Factors and Datum

Multiply By To obtain

Length

millimeter (mm) 0.03937 inch (in.)

meter (m) 3.281 foot (ft) 

kilometer (km) 0.6214 mile (mi)

Area

square kilometer (km2

) 0.004047 acre

Flow rate

millimeter per year (mm/yr) 25.4 inch per year (in/yr) 

Vertical coordinate information is referenced to North American Vertical Datum of 1988 

(NAVD 88).

Horizontal coordinate information is referenced to North American Datum of 1983 (NAD 83).

Elevation, as used in this report, refers to distance above the vertical datum.

Abbreviations

CORS Continuously Operating Reference Station

GPS Global Positioning System

InSAR interferometric synthetic aperture radar

NOAA National Oceanic and Atmospheric Administration

SAR synthetic aperture radar

USGS U.S. Geological Survey
Land Subsidence and Relative 

Sea-Level Rise in the Southern 

Chesapeake Bay Region

By Jack Eggleston and Jason Pope

The southern Chesapeake Bay region is experiencing land subsidence and rising water 

levels due to global sea-level rise; land subsidence and rising water levels combine to cause 

relative sea-level rise. Land subsidence has been observed since the 1940s in the southern 

Chesapeake Bay region at rates of 1.1 to 4.8 millimeters per year (mm/yr), and subsidence 

continues today.

This land subsidence helps explain why the region has the highest rates of sea-level rise on 

the Atlantic Coast of the United States. Data indicate that land subsidence has been responsible 

for more than half the relative sea-level rise measured in the region. Land subsidence increases 

the risk of flooding in low-lying areas, which in turn has important economic, environmental, 

and human health consequences for the heavily populated and ecologically important southern 

Chesapeake Bay region.

The aquifer system in the region has been compacted by extensive groundwater pumping in the region at rates of 1.5- to 3.7-mm/yr; this compaction accounts for more than half 

of observed land subsidence in the region. Glacial isostatic adjustment, or the flexing of the 

Earth’s crust in response to glacier formation and melting, also likely contributes to land 

subsidence in the region.

Aerial view of Little Creek and Joint Expeditionary Base Little Creek-Fort Story in Virginia 

Beach, Virginia. The Chesapeake Bay is seen in the upper right area of the photograph. 

Photograph by Steve Earley, The Virginian-Pilot, November 1998, used with permission.

 1
2 

Land subsidence makes 

coastal flooding more 

severe in the Hampton 

Roads area.

The southern Chesapeake Bay region consists of the Chesapeake Bay and adjoining 

estuaries, the Virginia Coastal Plain to the west and south, and the Delmarva Peninsula (also 

called the Eastern Shore) to the east. Rivers draining to the southern Chesapeake Bay include 

the Elizabeth, James, Rappahannock, and York, as well as numerous smaller streams and tidal 

channels. Because of the low-lying topography, land and sea elevations are in a delicate balance 

(fig. 1). The relatively flat topography means that small decreases in land elevations or small 

increases in sea levels can increase flooding potential in urban and undeveloped areas.

Hampton Roads is the sole large urban center in the southern Chesapeake Bay region, 

consists of 13 communities, and has a population of 1.7 million people (fig. 2; U.S. Census 

Bureau, 2010). Hampton Roads is home to one of the largest ports on the east coast of the 

United States and many military bases, including Norfolk Naval Shipyard, the world’s largest 

naval base. Many densely populated areas within Hampton Roads lie along the shores of tidal 

water bodies.

The southern Chesapeake Bay region also contains valuable natural and historical sites 

that are vulnerable to land subsidence and sea-level rise (Saunders and others, 2010). The 

Chesapeake Bay, as a whole, is the largest estuary in the United States and is home to hundreds 

of plant and animal species, including threatened and endangered species (Chesapeake Bay 

Program, 2011). The southern Chesapeake Bay region has more than a dozen wildlife refuges 

that protect important estuarine environments.

Land subsidence increases the rate of relative sea-level rise and helps explain why the 

southern Chesapeake Bay region has the highest rate of sea-level rise on the Atlantic Coast of 

the United States (Zervas, 2009). As communities in the region grapple with flooding problems 

and prepare for higher sea levels in the future, it is important to understand and potentially 

manage land subsidence.

Figure 1. Coastal flooding along the shore of the Elizabeth River in the Ghent neighborhood of 

Norfolk, Virginia, from a minor tide in February 2003. Interaction between water and land in the 

southern Chesapeake Region affects its renowned estuaries and urban and military infrastructure. 

Slight increases in water levels or decreases in land-surface elevations can increase the risk of 

flooding in low-lying areas. Photograph by Vasna Wilson, courtesy of The Virginian-Pilot, used 

with permission.
 3

$

$

!

!

!

^

^

YORK

WILLIAMSBURG

VIRGINIA BEACH

POQUOSON SURRY

SUFFOLK

SOUTHAMPTON

PORTSMOUTH

NORFOLK

NEWPORT NEWS

JAMES CITY

ISLE OF WIGHT

HAMPTON

GLOUCESTER

FRANKLIN

CHESAPEAKE

Eastern 

Shore

55H 1

372428076561501 

VIRGINIA

NORTH CAROLINA

VIRGINIA

Continuously Operating Reference Station (CORS), name, and rate 

of subsidence for years indicated (National Geodetic Survey, 2013) 

USGS extensometer station, location, number, local name, and 

rate of subsidence for years indicated (Pope and Burbey, 2004)

U.S. Geological Survey (USGS) groundwater monitoring well, 

local name, and identification number

National Oceanic and Atmospheric Administration tidal station, 

location, and identification number (Zervas, 2009)

EXPLANATION

West Point

$

^

!

Chesapeake Bay

Bridge Tunnel

Impact crater outer rim

NORTH CAROLINA

VIRGINIA

Chesapeake Bay

Atlantic 

Ocean

James River

York River

Rappahannock River

Blackwater River

DRV6 

-3.3 mm/yr

2006–2011

VIMS 

-3.4 mm/yr

1999–2011

VAGP 

-2.7 mm/yr

2007–2011

Franklin 364101076544802 

55B 60

-1.5 mm/yr, 1979–1995

Suffolk 364512076343701 

58C 52

-3.7 mm/yr, 1982–1995

Kiptopeke 8632200

Portsmouth 8638660

Sewells Point 8638610

Gloucester Point 8637624

77° 76°30' 76°

37°30'

37°

0

0

10

10

20 MILES

20 KILOMETERS

Map made from USGS and Virginia Department of Game and Inland Fisheries data

Virginia State plane projection

Virginia south Federal Information Processing Standard (FIPS) 4502

North American Datum 1983 (NAD83) 

Coastal Plain

Chesapeake Bay Atlantic Ocean

Fall Line

VA

MD

MD

NC

WV

DE

VA

DC

Hampton 

Roads

MD

VA

NC

Figure 2. Stations for monitoring land and sea elevations in the southern Chesapeake Bay region. The Atlantic Coastal Plain is shown 

in light gray shading. Hampton Roads Planning District Commission (HRPDC) communities within the Atlantic Coastal Plain are shown 

in white shading. mm/yr, millimeters per year; NOAA, National Oceanic and Atmospheric Administration; USGS, U.S. Geological Survey; 

VA, Virginia.
S

l

l 

i

bsidence

Current

shoreline

Future shoreline

with sea-level 

rise only

Future shoreline

with sea-level rise 

and land subsidence

Current land surface

Future land surface

Current sea level

Future sea level Sea-level rise

Land subsidence

Current

shoreline

Future shoreline

with sea-level 

rise only

Future shoreline

with sea-level rise 

and land subsidence

Current land surface

Future land surface

Current sea level

Future sea level

4 

Description of Land Subsidence

Land subsidence is the sinking or lowering of the land surface. Most land subsidence 

in the United States is caused by human activities (Galloway and others, 1999). Two wellstudied cases of land subsidence are in the Houston-Galveston, Texas, area and the Santa Clara 

Valley, California. Land sank by as much as 3 meters (m) over 50 years because of intensive 

groundwater withdrawals in the two areas, as well as petroleum extraction in Texas, resulting 

in increased coastal flooding (Poland, 1984; Galloway and others, 1999; Bawden and others, 

2012). Regional authorities were established in the two areas to manage water use and land 

subsidence. The regional authorities set up monitoring networks and enlisted scientists to study 

the problem. Ultimately, the communities adopted new water-management practices to prevent 

land subsidence, including relocating groundwater withdrawals away from the coast, substituting surface water for groundwater supplies, and increasing aquifer recharge. In the Santa Clara 

Valley, subsidence has mostly been stopped and, in the Houston-Galveston area, subsidence has 

been slowed, particularly along vulnerable shorelines (Bawden and others, 2012).

Rates and locations of land subsidence change over time so accurate measurements and 

predictive tools are needed to improve understanding of land subsidence. Although rates 

of land subsidence are not as high on the Atlantic Coast as they have been in the HoustonGalveston area or the Santa Clara Valley, land subsidence is important because of the low-lying 

topography and susceptibility to sea-level rise in the southern Chesapeake Bay region.

Why Land Subsidence is a Concern in the Southern 

Chesapeake Bay Region

Land subsidence can increase flooding, alter wetland and coastal ecosystems, and damage 

infrastructure and historical sites. Because land subsidence contributes to relative sea-level rise 

in the region, it is important for regional planners to understand why, where, and how fast it is 

occurring, now and in the future.

Land Subsidence Contributes to Relative Sea-Level Rise

Land subsidence contributes to the relative sea-level rise that has been measured in the 

Chesapeake Bay (fig. 2). However, tidal-station measurements of sea levels do not distinguish 

between water that is rising and land that is sinking—the combined elevation changes are 

termed relative sea-level rise. Global sea-level rise and land subsidence increase the risk of 

coastal flooding and contribute to shoreline retreat (fig. 3).

Land subsidence is the 

sinking or lowering of the 

land surface.

Figure 3. Shoreline retreat caused by a combination of sea-level rise and land subsidence.
 5

Land Subsidence Increases Flood Risk

As relative sea levels rise, shorelines retreat and the 

magnitude and frequency of near-shore coastal flooding 

increase. Although land subsidence can be slow, its effects 

accumulate over time. This has been an expensive problem 

in the Houston-Galveston area and the Santa Clara Valley 

(Galloway and others, 1999) and likely contributes to 

current flooding problems in the southern Chesapeake Bay 

region. Analysis by McFarlane (2012) found that between 

59,000 and 176,000 residents living near the shores of the 

southern Chesapeake Bay could be either permanently 

inundated or regularly flooded by 2100. This estimate was 

based on 2010 census data, using the spring high-tide as a 

reference elevation and assuming a 1-m relative sea-level 

rise. Damage to personal property was estimated to be 

$9 billion to $26 billion, and 120,000 acres of ecologically 

valuable land could be inundated or regularly flooded, under 

these same assumptions. Historic and cultural resources are 

also vulnerable to increased flooding from relative sea-level 

rise in the southern Chesapeake Bay, particularly at shoreline sites near tidal water, such as the 17th century historic 

Jamestown site (fig. 4).

Land subsidence can also increase flooding in 

areas away from the coast. Low-lying areas, such as the 

Blackwater River Basin (fig. 2), can be subject to increased 

flooding as the land sinks. Locations along the Blackwater 

River in the city of Franklin and the counties of Isle of Wight 

and Southampton have experienced large floods in recent 

years (fig. 5; Federal Emergency Management Agency, 

2002). Land subsidence may be altering the topographic 

gradient that drives the flow of the river and possibly 

contributing to the flooding.

Figure 4. Jamestown, Virginia, next to the James River showing 

the reconstructed colonial-era fort wall. Photograph courtesy of 

The Colonial Williamsburg Foundation, used with permission.

Figure 5. Downtown Franklin, Virginia, during flooding caused 

by Hurricane Floyd in September 1999. Photograph by John H. 

Sheally II, courtesy of The Virginian-Pilot, used with permission. 
Land Subsidence Can Damage Wetland and Coastal Marsh Ecosystems

Wetland and marsh ecosystems in low-lying coastal areas are very sensitive to small 

changes in elevation (Cahoon and others, 2009). Salt marshes, which are widespread in the 

southern Chesapeake Bay region, are dependent on tidal dynamics for their existence. Small 

changes in either land or sea elevations can alter sediment deposition, organic production 

and plant growth, and the balance between fresh water and seawater (fig. 6; Morris and 

others, 2002).

Shoreline environments also are affected by land subsidence. When land subsides, it 

subjects shorelines to increased wave action, increasing erosion and washover. This type of 

damage is happening in the Chesapeake Bay because of relative sea-level rise (Erwin and 

others, 2011; Kirwan and Guntenspergen, 2012; Kirwan and others, 2012). Major changes in 

the coastal and marine ecosystems of the southern Chesapeake Bay are expected to be caused 

by relative sea-level rise (Gutierrez and others, 2009); these changes will likely be more severe 

if land subsidence continues.

Land Subsidence Can Damage Infrastructure

Infrastructure such as buildings, bridges, pipes, and canals can be damaged from relative 

groundwater rise or from differential settling in areas with high subsidence gradients (Galloway 

and others, 1999). As land sinks and sea level continues to rise, groundwater levels rise towards 

the land surface in coastal areas, which can cause problems for subterranean structures, septic 

fields, buried pipes and cables, and infrastructure not designed for elevated groundwater levels. 

Storm and wastewater sewers in urban areas are vulnerable because land subsidence can alter 

the topographic gradient driving the flow through the sewers, causing increased flooding and 

more frequent sewage discharge from combined sewer overflows.

6 

A great egret takes to the 

air along the Lynnhaven 

River in Virginia Beach, 

Virginia, at a conservation 

area that features oyster 

beds, wetlands, and a 

maritime forest. Photograph 

by L. Todd Spencer, The 

Virginian-Pilot, July 2010, 

used with permission.

Figure 6. Forces and processes that influence marsh and wetland development. Environmental 

drivers (white boxes) and accretionary processes (yellow boxes) influence vertical marsh and 

wetland development. Modified from Cahoon and others (2009). CO2, carbon dioxide.

Nutrient input

Altered river flows

Storms

Subsidence

Salinity

Flooding

Biomass accumulation

Decomposition

Nutrients

Sedimentation and erosion

Sea level rise and tides

Disturbance Elevated 

atmospheric

CO2

Plant growth and turnover

Soil elevation

Rates of land subsidence 

vary with location and 

change over time.
 7

How Land Subsidence is Measured

There are several reliable and accurate techniques for measuring land subsidence. 

Multiple monitoring techniques are often used together to understand different aspects of 

land subsidence (table 1). Rates and locations of land subsidence change over time, so repeat 

measurements at multiple locations are often needed to improve understanding of the complex 

phenomenon and guide computer models that forecast future subsidence. Extensometers 

measure changes in aquifer-system thickness, whereas other methods measure land surface 

elevation, from which subsidence is calculated by subtracting measurements over time.

Borehole Extensometers

A borehole extensometer measures compaction or 

expansion of an aquifer system independently of other vertical 

movements, such as crustal and tectonic motions (Galloway 

and others, 1999). An extensometer measures changes in 

aquifer-system thickness by recording changes in the distance 

between two points in a well (fig. 7). Usually the two 

measurement points are established at the top and bottom of a 

well to measure total aquifer-system compaction between the 

land surface and the bottom of the aquifer system (fig. 8). 

Alternatively, specific intervals within a well can be measured, 

for example, to measure compaction of just one aquifer within 

a layered aquifer system. Extensometer measurements are often 

combined with surface monitoring techniques to determine the 

portion of total land subsidence attributable to aquifer-system 

compaction (Poland, 1984).

B

A

Figure 7. The borehole extensometer in Franklin, Virginia. 

A, Survey station house; photograph by Jason Pope, U.S. 

Geological Survey ; B, recording equipment; photograph by 

Chuck Heywood, U.S. Geological Survey.

Table 1. Land subsidence monitoring methods.

[GPS, Global Positioning System; InSAR, interferometric synthetic aperture radar]

Method Type of data

Measures aquifersystem compaction 

independently

Spatial coverage Temporal detail

Borehole extensometer Aquifer-system thickness at one location, 

continuous record Yes Low High

Tidal station Sea elevation at one location, continuous 

record No Low High

Geodetic surveying Land elevations at one or several locations, 

multiple times or continuous record No Low to moderate Low to high

Remote sensing (InSAR) Land elevations over a wide area, at 

multiple times No High Moderate
Bedrock

Layered aquifer system

10

Well casing

Extensometer pipe

Bottom of extensometer pipe 

anchored to bedrock

Tensioner to overcome 

friction between 

extensometer pipe and 

well casing

Steel table

Steel tape

Compaction recorder

Table anchored

to surface soil

Land surface

8 

Figure 8. The borehole extensometer in Franklin, Virginia. Modified from Pope (2002).
 9

Tidal Stations

A tidal station measures sea elevation at one location. To determine long-term trends, 

sea-level measurements are averaged over time to remove the effect of waves, tides, and other 

short-term fluctuations. In the southern Chesapeake Bay, tidal stations have been in operation 

for many decades (fig. 2; table 2). Tidal station data are valuable because they indicate relative 

sea-level rise.

Tidal station data are valuable because they indicate 

relative sea-level rise.

Table 2. Relative sea-level rise at selected National Oceanic and Atmospheric Administration tidal 

stations in the southern Chesapeake Bay region.

[Data are from Zervas (2009). Locations of monitoring stations are shown in figure 2. CI, confidence interval; mm, 

millimeters; mm/yr, millimeters per year; %, percent]

ID Site name Period 

Rate of relative sea-level rise

Measured,

(mm/yr) 95% CI

8632200 Kiptopeke, Virginia 1951–2006 3.5 ±0.42

8637624 Gloucester Point, Virginia 1950–2006 3.8 ±0.47

8638610 Sewells Point, Virginia 1927–2006 4.4 ±0.27

8638660 Portsmouth, Virginia 1935–2006 3.8 ±0.45

Average 3.9 ±0.40

Geodetic Surveying

Geodetic surveying is the measurement of land surface coordinates. Geodetic surveying 

is most commonly performed either with traditional optical leveling equipment or with Global 

Positioning System (GPS) technology that reads signals from satellites to obtain very detailed 

location and time information. Where historical geodetic survey records are available, as they 

are for the southern Chesapeake Bay region, geodetic surveying can be useful to determine 

cumulative land subsidence over many decades. Benchmark stations are established and, for 

as long as they remain undisturbed, can be surveyed multiple times to determine elevation 

changes between surveys.

The National Geodetic Survey manages the Continuously Operating Reference Station 

(CORS) network, a network of long-term GPS stations throughout the United States that 

includes stations in the southern Chesapeake Bay region (fig. 2). Each CORS station continuously records three-dimensional position data (north-south, east-west, and up-down), allowing 

rates of change to be calculated over time (Snay and Soler, 2008). A CORS station records 

ground position at one site and is designed to operate for many years.

In addition to stationary GPS sites such as the CORS stations, portable GPS receivers can 

be used to expand spatial coverage. In the Houston-Galveston area, GPS receivers mounted on 

trailers have been used to collect data at up to four different sites each month (Galloway and 

others, 1999; Bawden and others, 2012). The portable GPS approach had acceptable subcentimeter accuracy, gave greater spatial coverage than stationary GPS would have, and had a lower 

cost than interferometric synthetic aperture radar (InSAR) technology.
10 

InSAR is a remote 

sensing technique used to 

investigate land surface 

deformation resulting from 

land subsidence.

InSAR

The remote sensing technique InSAR has been used to investigate surface deformation resulting from land subsidence (Galloway and Hoffman, 2007). With InSAR, as little as 

5 millimeters (mm) of elevation change can be measured over hundreds or thousands of square 

kilometers with a horizontal spatial resolution down to 20 m (Pritchard, 2006). Maps called 

interferograms that show land-surface elevation changes are produced by combining two 

synthetic aperture radar (SAR) images acquired by multiple satellite or airborne passes over the 

same area at different times. InSAR analysis has the advantage of measuring subsidence over a 

large area, whereas traditional geodetic leveling and GPS surveying are performed at only one 

or a handful of locations during a survey (Sneed and others, 2002; Stork and Sneed, 2002).

There are potential limitations to using InSAR in the southern Chesapeake Bay region. 

Subsidence rates determined by InSAR might have errors that are larger than the subsidence rates observed in the region (1.1 to 4.8 mm/yr). The region’s dense vegetation and high 

humidity would create spurious radar signals, require the use of persistent scatter techniques, 

and result in lower measurement resolution than is found in more arid regions (Raucoules 

and others, 2009). In addition, available satellite data cover only a relatively short time span. 

The best available synthetic aperture radar (SAR) satellite data for the southern Chesapeake 

Bay region cover from 1992 to 2000, so the time of accumulated subsidence determined from 

these data would be no more than 8 years. Despite these limitations, InSAR could be used to 

identify hotspot areas of subsidence. Such mapping could be useful for identifying unexpected 

areas of subsidence, focusing attention on important areas, and picking locations for other 

ground-based subsidence monitoring techniques (Michelle Sneed, U.S. Geological Survey, 

written commun., 2012).

Causes of Land Subsidence

It is important to know the causes of land subsidence so 

that it can be more effectively managed. Most land subsidence in the United States is caused by human activities 

(Galloway and others, 1999), with groundwater withdrawals 

responsible for about 80 percent of land subsidence in the 

United States. Causes of subsidence that are most relevant to 

the southern Chesapeake Bay region include aquifer-system 

compaction caused by groundwater withdrawals and glacial 

isostatic adjustment.

Location of maximum subsidence in United States 

identified by research efforts of Joseph Poland 

(pictured) - San Joaquin Valley southwest of 

Mendota, California. Land subsidence in this area 

was caused by excessive groundwater pumping. 

Signs on pole show approximate altitude of land 

surface in 1925, 1955, and 1977. Photograph from 

Galloway and others (1999), USGS.
 11

Aquifer-System Compaction From Groundwater Withdrawals

When groundwater is pumped from an aquifer system, pressure decreases. The pressure 

change is reflected by water levels in wells, with water levels decreasing as aquifer-system 

pressure decreases. This is happening over most of the southern Chesapeake Bay region, 

with the greatest water-level decreases seen near the pumping centers of Franklin and West 

Point, Virginia (fig. 9). As water levels decrease, the aquifer system compacts, causing the 

land surface above to subside (fig. 10). Water levels have decreased over the entire Virginia 

Coastal Plain in the Potomac aquifer, which is the deepest and thickest aquifer in the southern 

Chesapeake Bay region and supplies about 75 percent of groundwater withdrawn from the 

Virginia Coastal Plain aquifer system (Heywood and Pope, 2009).

The amount of aquifer-system compaction is determined by three factors: water-level 

decline, sediment compressibility, and sediment thickness. If any of these three factors increase 

in magnitude, then the amount of aquifer-system compaction and land subsidence increases. 

Because all three of these factors vary spatially across the southern Chesapeake Bay region, 

rates of land subsidence caused by aquifer-system compaction also vary spatially across 

the region.

The Virginia Coastal Plain aquifer system consists of many stacked layers of sand and 

clay (fig. 11). Although groundwater is withdrawn primarily from the aquifers (sandy layers), 

most compaction occurs in confining units and clay lenses, the relatively impermeable layers 

sandwiched between and within the aquifers (Pope and Burbey, 2004). The compression of 

clay layers is mostly nonrecoverable, meaning that, if groundwater levels later recover and 

increase, then the aquifer system does not expand to its previous volume and the land surface 

does not rise to its previous elevations (Pope, 2002). Konikow and Neuzil (2007) estimated 

that 95 percent of the water removed from storage in the Virginia Coastal Plain aquifer system 

between 1891 and 1980 was derived from the confining layers.

The timing of aquifer-system compaction is also important. Compaction can continue for 

many years or decades after groundwater levels drop. When groundwater is pumped from an 

aquifer, pressure decreases in the aquifer. The pressure decrease then slowly propagates into 

clay layers that are adjacent to or within the aquifer. As long as pressure continues to decrease 

in the clay layers, compaction continues.

The layered sediments of the Virginia Coastal Plain aquifer system range in grain size 

from very fine (silts and clays) to coarse (sand and shell fragments) (McFarland and Bruce, 

2006). Based on the hydrogeologic framework of McFarland and Bruce (2006) and Heywood 

and Pope (2009), confining layers outside the meteor impact crater occupy about 16 percent 

of the total aquifer-system thickness, an average of 100 m out of the total average thickness 

of 619 m. These confining layers have high specific storage (compressibility) estimated to be 

0.00015 per meter (Pope and Burbey, 2004). Clay layers overlying and within the Potomac 

aquifer are compressing as aquifer pressure decreases migrate vertically and laterally from 

pumping wells.
12 

VIRGINIA

NORTH CAROLINA

Eastern 

Shore

Impact Crater Outer Rim

Franklin

West Point

SUFFOLK

SURRY

SOUTHAMPTON

CHESAPEAKE

ISLE OF WIGHT

YORK

GLOUCESTER

VIRGINIA BEACH

HAMPTON

JAMES CITY

NEWPORT

NEWS

NORFOLK

PORTSMOUTH

POQUOSON

FRANKLIN

WILLIAMSBURG

Blackwater River

Chesapeake Bay

Atlantic Ocean

James River

York River

Rappahannock River

Groundwater withdrawal center

Line of equal groundwater water level decline 

 (predevelopment to 2008)—Shows change in elevation. 

 Contour interval is 5 meters

EXPLANATION

Groundwater

level decrease,

in meters

0

0 10

20 MILES

20 KILOMETERS

77°30' 77° 76°30' 76°

37°30'

37°

36°30'

Map made from U.S. Geological Survey and Virginia Department of Game and Inland Fisheries data

Virginia State plane projection

Virginia south Federeal Information Processing Standard (FIPS) 4502

North American Datum 1983 (NAD83) 

50

40

45

35

55 60

25

30

15

10

5

35

30

35

25

5

15

20

10

20

15

10

10

40

45

50

25

30

40

45

20

25

20

0

65

20

U.S. Geological Survey extensometer station

Figure 9. Groundwater water-level decreases from 1900 to 2008. Modified from Heywood and Pope (2009). 
 13

Land surface

Land 

subsidence 

Sandy aquifer

Clay confining unit

Monitoring 

well

Clay lens

Water table

Water table

Total 

aquifer

system

compaction

Sandy aquifer

Clay confining unit

Sandy aquifer

A. Before pumping B. After pumping

Arrows represent

compaction due

to pumping

Figure 10. Aquifer-system compaction caused by groundwater withdrawals A, before and B, after 

pumping. Modified from Galloway and others (1999).

VERTICAL SCALE GREATLY EXAGGERATED

WEST EAST

Surficial aquifer

Chesapeake

Bay

0 10 20 MILES

0 10 20 KILOMETERS

Fall Zone

Elevation, in meters above or below NAVD88

Exmore clast

confining unit

Chesapeake Bay impact crater

150

0

-150

-300

-450

Potomac aquifer

Piney Point aquifer

Yorktown-Eastover aquifer

Aquia aquifer

Calvert confining unit

Nanjemoy-Marlboto confining unit

Potomac confining unit

Bedrock

0

-150

-300

-450

Chickahominy confining unit

Exmore matrix confining unit

Figure 11. Section illustrating layering in the Virginia Coastal Plain aquifer system from west to east. Elevation relative to North 

American Vertical Datum of 1988 (NAVD88). Modified from McFarland and Bruce (2006).
14 

Glacial Isostatic Adjustment

Crystalline bedrock underlies the layered sediments of the Virginia Coastal Plain aquifer 

system. Bedrock is not solid and unyielding but actually flexes and moves in response to stress. 

Bedrock in the mid-Atlantic region is moving slowly downward in response to melting of the 

Laurentide ice sheet that covered Canada and the northern United States during the last ice age 

(Sella and others, 2007; Boon and others, 2010). When the ice sheet still existed, the weight of 

the ice pushed the underlying Earth’s crust downward and, in response, areas away from the ice 

sheet were forced upward (called glacial forebulge). The southern Chesapeake Bay region is 

in the glacial forebulge area and was forced upward by the Laurentide ice sheet. The ice sheet 

started melting about 18,000 years ago and took many thousands of years to disappear entirely. 

As the ice melted and its weight was removed, glacial forebulge areas, which previously had 

been forced upward, began sinking and continue to sink today. This movement of the Earth’s 

crust in response to ice loading or melting is called glacial isostatic adjustment. Data from GPS 

measurements and carbon dating of marsh sediments indicate that regional land subsidence 

in response to glacial isostatic adjustment in the southern Chesapeake Bay region may have a 

current rate of about 1 mm/yr (Engelhart and others, 2009; Engelhart and Horton, 2012). This 

downward velocity rate is uncertain and probably not uniform across the region.

Other Causes of Land Subsidence

There are other causes of land subsidence, but there is currently little or no evidence that 

these other causes are important to regional subsidence processes in the southern Chesapeake 

Bay region. However, they are mentioned here and may warrant further study.

Bedrock dissolution is important in parts of the United States with evaporite (for example 

gypsum) or carbonate (for example limestone) rocks, but is unlikely to be contributing to 

land subsidence in the southern Chesapeake Bay region where bedrock is mostly crystalline 

(McFarland and Bruce, 2006).

Drainage and degradation of organic soils is a common cause of land subsidence in some 

parts of the United States (Galloway and others, 1999). Numerous marshes have been drained 

in the southern Chesapeake Bay region during the past few centuries to control mosquito 

populations or to create new land for agriculture and development. However, drained organic 

soils are not prevalent at the monitoring sites shown in figure 2 and, although degradation of 

organic soils may contribute locally to subsidence in some areas, it is not likely to be contributing to regional land subsidence.

Settling of fill and disturbed soils can cause land to sink. This may be happening in local 

areas where construction has disturbed soils, marshes have been filled in, or islands have been 

constructed, such as the islands constructed for the Chesapeake Bay Bridge Tunnel. However, 

settling of fill and disturbed soils cannot explain the subsidence observed across the southern 

Chesapeake Bay region.

Volcanic disturbances and tectonic motion related to continental crust movements are 

thought to have negligible contribution to land elevation changes along the Atlantic Coast 

of the United States because there are no volcanoes or tectonic plate margins in the region 

(Engelhart and others, 2009).

Settling of impact crater sediments associated with the Chesapeake Bay meteor crater 

(figs. 9 and 11) is an unlikely cause of current land subsidence in the region because the meteor 
 15

struck about 35 million years ago (Powars and Bruce, 1999). The passage of time since the 

meteor impact has been so great that, even if it was conservatively assumed that subsidence 

rates had stayed constant during the past 1 million years rather than decreasing, a rate of 

1 mm/yr would equate to 1 kilometer of subsidence, which is not compatible with our current 

understanding of regional geology (McFarland and Bruce, 2006). Measured subsidence rates 

also indicate that the crater has the indirect effect of reducing modern-day subsidence caused 

by aquifer-system compaction, because the low-permeability sediments associated with the 

impact crater (Heywood and Pope, 2009) reduce groundwater level decreases within the rim of 

the crater (fig. 9).

Rates of Land Subsidence and Sea-Level Rise in the 

Southern Chesapeake Bay Region

Land subsidence has been known and observed in the southern Chesapeake Bay region for 

many decades and is a factor that should be considered by urban planners and natural resource 

managers. Some aspects of the subsidence problem, such as a full understanding of causes, 

spatial variability, and historical and future subsidence rates over time, would benefit from 

additional research.

Measured Rates of Land Subsidence

Land subsidence in the southern Chesapeake Bay region was first documented by 

Holdahl and Morrison (1974), who reported results of geodetic surveys completed between 

1940 and 1971 and found land surfaces across the region were sinking at an average rate of 

2.8 mm/yr with rates ranging from 1.1 to 4.8 mm/yr (fig. 12; table 3). The two areas where 

subsidence rates were fastest roughly coincide with groundwater pumping centers at Franklin 

and West Point. Measurements of land subsidence are currently (2013) made at CORS stations 

in the region. The National Geodetic Survey has computed velocities for three of these stations 

(fig. 2) between 2006 and 2011 and found an average subsidence rate of 3.1 mm/yr (table 3; 

Snay and Soler, 2008; National Geodetic Survey, 2013).

Aquifer-system compaction was measured with extensometers at two locations in the 

region, at Franklin from 1979 to 1995 and at Suffolk from 1982 to 1995 (figs. 2 and 13; Pope 

and Burbey, 2004). The extensometers showed 24.2 mm of total compaction at Franklin 

from 1979 through 1995 (1.5 mm/yr) and 50.2 mm of total compaction at Suffolk from 1982 

through 1995 (3.7 mm/yr). Rates of compaction were correlated to groundwater-level decreases 

and to the aggregate thickness of compressible sediments at each location. The total thickness of compressible fine-grained sediments is 130.8 m at Suffolk and 62.7 m at Franklin. 

Water levels in the Potomac aquifer during the period of compaction measurement decreased 

more at Suffolk than at Franklin, about 5 m versus about 2 m. Aquifer-system compaction 

has not been measured at any other locations in the southern Chesapeake Bay region but it 

likely affects most of the region because large water-level decreases in the aquifer system are 

widespread (fig. 9).

Land subsidence in the 

Hampton Roads area of 

the southern Chesapeake 

Bay region has averaged 

about 3 mm/yr since 1940. 

Measured rates range from 

1.1 to 4.8 mm/yr.
16 

Chesapeake Bay

Atlantic Ocean

James River

York River

Rappahannock River

Franklin

West Point

Boykins

-3.2 (0.9)

Leveling station, and land elevation change rate in millimeters 

per year (standard deviation)

Line of equal land elevation change rate interpolated 

from leveling station measurements—Shown in millimeters 

per year. Interval is variable

-3.2

Groundwater withdrawal center

Geodetic leveling from

Holdahl and Morrison (1974)

-3.2

0 5 10 15 20 MILES

EXPLANATION

0 10 20 KILOMETERS

Impact Crater Outer Rim

77°30' 77° 76°30' 76°

37°30'

37°

SUFFOLK

SURRY

SOUTHAMPTON CHESAPEAKE

ISLE OF WIGHT

YORK

GLOUCESTER

VIRGINIA BEACH

HAMPTON

JAMES CITY

NEWPORT

NEWS

NORFOLK

PORTSMOUTH

POQUOSON

FRANKLIN

WILLIAMSBURG

Toano

-2.1 (0.9)

Norfolk

-2.8 (0.5)

Boykins

-3.2 (0.9)

Westland

-1.5 (1.3) 

Lee Hall

-3.1 (0.8)

Kiptopeke

-1.1 (0.7)

West Point

-3.8 (1.0)

Smithfield

-3.3 (0.7)

Carrsville

-4.8 (0.8)

Spring 

Grove

-1.6 (0.9)

Williamsburg

-3.0 (0.8)

Providence 

Forge

-3.6 (1.3)

Hampton Roads

(Sewell’s Pt.)

-2.4 (0.5)

Saluda

-3.1 (1.0) Richmond

-1.9 (1.9)

Yorktown

-3.8 (1.0)

-1.6

-2.8

-4.0

-3.6

-4. 4

-2.0

-1.6

-2.4

-2.0

-2.4

-2.0

-2.0

-1.2

-1.6

-2.4

-2.8

-2.8

-3.2

-2.8

-2.4

Map made from U.S. Geological Survey and Virginia Department of 

Game and Inland FIsheries data

Virginia State plane projection

Virginia south Federal Information Processing Standard (FIPS) 4502

North American Datum 1983 (NAD83) 

VIRGINIA

NORTH CAROLINA

Figure 12. Land elevation change rates from 1940 through 1971. Adapted from Holdahl and Morrison (1974). Contours indicate lines 

of equal land elevation change rate (mm/year) and negative elevation change rates indicate subsidence. Values in parentheses are 

standard deviations.
 17

-5

0

5

10

15

20

25

30

35

40

45

50

55

1979 1981 1983 1985 1987 1989 1991 1993 1995 1997

Cumulative compaction, in millimeters

Year

Suffolk

Franklin

Figure 13. Aquifer-system 

compaction measured by 

borehole extensometers 

in Franklin, Virginia, at U.S. 

Geological Survey (USGS) 

site 364101076544802 and in 

Suffolk, Virginia, at USGS site 

364512076343701. Modified 

from Pope (2002). 

Sea-Level Rise and Subsidence in the 

Southern Chesapeake Bay Region

Multiple types of data describe land subsidence in the southern Chesapeake Bay region (table 3). There are some 

inconsistencies between measured subsidence rates, which are expected given the variety of data, the different 

times of measurement, and the multiple locations measured. However, the data paint a clear overall picture of land 

subsidence in the region during the past 75 years. Relative sea-level rise has been 3.5 to 4.4 mm/yr (table 2). Land 

subsidence, measured to be 1.1 to 4.8 mm/yr, causes more than half the relative sea-level rise (fig. 12). Aquifersystem compaction estimated to be 1.5 to 3.7 mm/yr can explain the majority of observed land subsidence.

Table 3. Observed sea-level rise and subsidence in the southern Chesapeake Bay region.

[IPCC, Intergovernmental Panel on Climate Change; mm/yr , millimeters per year; NA, not available; NGS, National Geodetic Survey; NOAA, National 

Oceanic and Atmospheric Administration; SD, standard deviation; USCG, U.S. Coast Guard; USGS, U.S. Geological Survey]

What was measured Monitoring 

technique Agency Number of stations

Rate,1

 in mm/yr

Period Average Low High SD

Global data

Estimated average 

global sea-level rise

Various IPCC2 NA 1961–2003 1.8 NA NA NA

Southern Chesapeake Bay region data

Aquifer compaction Extensometer USGS3 2 1979–1995 –2.6 –1.5 –3.7 NA

Land subsidence Geodetic survey NGS4 17 1940–1971 –2.8 –1.1 –4.8 0.8

Land subsidence Fixed GPS NOAA/USCG5 3 2006–2011 –3.1 –2.7 –3.4 0.4

Relative sea-level rise Tidal station NOAA6 4 1927–2006 3.9 3.5 4.4 0.2

1

Negative values indicate downward motion (land subsidence), positive values upward motion.

2

Data are from Bindoff and others (2007).

3

Data are from Pope and Burbey (2004).

4

Data are from Holdahl and Morrison (1974).

5

Data are from Snay and Soler (2008) and National Geodetic Survey (2013) from Continuously Operating Reference Station (CORS) network.

6

Data are from Zervas (2009).
Rates of Sea-Level Rise

Relative sea-level rise measured at four National Oceanic and Atmospheric Administration 

(NOAA) tidal stations (fig. 2; table 2) averaged 3.9 mm/yr from about 1950 through 2006. At 

the Sewells Point tidal station in Norfolk, Va., rising sea levels have been recorded since 1927 

(fig. 14; table 2). Sea level at Sewells Point rose at an average rate of 4.4 mm/yr from 1927 to 

2006, with a 95 percent confidence interval of ±0.27 mm/yr (Zervas, 2009). In comparison, 

global average sea levels have been rising at about 1.8 mm/yr. Although rates of absolute sealevel rise (rise due just to increases in ocean volume) can vary substantially from one location 

to another and change over time (Boon and others, 2010; Sallenger and others, 2012), the 

global average rate of 1.8 mm/yr from 1961 to 2003 is a widely accepted global benchmark rate 

(Bindoff and others, 2007, p. 410). The difference between the average sea-level rise computed 

from the four NOAA tidal stations in the study area (3.9 mm/yr) and the benchmark global 

rate (1.8 mm/yr) is 2.1 mm/yr, which is an estimate of the average rate of land subsidence at 

the four NOAA stations. These numbers indicate that land subsidence has been responsible 

for more than half the relative sea-level rise measured in the southern Chesapeake Bay region. 

Rates of land subsidence vary with location, as can be seen from the different rates of sea-level 

rise at the four NOAA stations and the variable rates of subsidence measured by Holdahl and 

Morrison (1974). More research will be required to better understand the details of how land 

subsidence contributes to relative sea-level rise in this region.

EXPLANATION

-0.2

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1900 1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 2010 2020

Elevation, in meters NAVD 88

Year

Sewell’s Point monthly mean sea level

Average global sea level

Average trend of Sewell’s Point monthly means

Starting elevation in 1927

18 

Figure 14. Monthly mean 

sea levels at Sewells Point in 

Norfolk, Virginia, at National 

Oceanic and Atmospheric 

Administration station 8638610; 

the global average sea-level 

rise rate of 1.8 millimeters 

per year is also shown as 

a comparison (Bindoff and 

others, 2007, p. 410). Land 

subsidence contributes to the 

high rate of sea-level rise at 

Sewells Point relative to the 

average global sea-level rise.
Links Between Groundwater Withdrawals and 

Land Subsidence

Aquifer-system compaction may be responsible for the 

majority of land subsidence in the southern Chesapeake Bay 

region based on average measured land subsidence rates of 

about 2.8 mm/yr and measured average compaction rates of 

2.6 mm/yr (table 3). The aquifer-system compaction is caused 

by high groundwater withdrawal rates that have lowered 

water levels.

Groundwater withdrawal rates in the region increased 

sharply in the 20th century (fig. 15) as modern pumping technology was widely adopted (Heywood and Pope, 2009). The 

many decades of increasing groundwater withdrawals have 

caused groundwater levels to decrease across the southern 

Chesapeake Bay region (fig. 9). The water levels in USGS 

groundwater monitoring well 55H 1 (site 372428076561501; 

fig. 16) give a typical example of water level decreases 

over time in the Potomac aquifer. Water levels are expected 

to continue decreasing for many years, even if pumping 

rates do not increase further, because of delay caused by 

compressibility of the aquifer system (Konikow and Neuzil, 

2007; Mace, 2011).

The complexity of the structure of the aquifer system and 

the dynamic water-level adjustment to pumping complicate 

understanding of aquifer-system compaction in the southern 

Chesapeake Bay region. Because aquifer-system compaction is a major contributor to total land subsidence in the 

region, an important first step towards understanding land 

subsidence is to understand compaction. Layer thickness and 

sediment compressibility vary spatially according to complex 

stratigraphy in the region, which has been mapped in detail by 

McFarland and Bruce (2006). Water-level decreases also vary 

with location (fig. 9) and across the various layers in the aquifer system. To garner a better understanding of land subsidence will likely require construction of a computer model to 

simulate aquifer-system compaction. Such a model could also 

be used to estimate future subsidence and examine alternate 

management scenarios to reduce or mitigate land subsidence.

0

20

40

60

80

100

120

140

1900 1920 1940 1960 1980 2000 2020

Groundwater withdrawals, in million gallons per day

Year

Figure 15. Groundwater withdrawal rates from Virginia Coastal 

Plain aquifers from 1900 to 2008. Modified from Heywood and 

Pope (2009).

Figure 16. Water levels in the Potomac aquifer at U.S. 

Geological Survey (USGS) groundwater monitoring well 55H 1 

(site 372428076561501) in New Kent County, Virginia. Well location 

is shown in figure 2.

circ_eggleston_fig16.ai

-10

-20

-30

0

1950 1960 1970 1980 1990 2000 2010 2020

Water elevation, in meters above North 

American Vertical Datum of 1988

Year

EXPLANATION 

Water level measurement

Inferred water level

Groundwater withdrawal rates in 

the region increased sharply in 

the 20th century

Photograph courtesy of NCRS

 19
Major Conclusions

•	 Land subsidence and global sea-level rise combine to cause relative sea-level rise in the 

southern Chesapeake Bay region.

•	 Land subsidence causes more than half of the observed relative sea-level rise.

•	 Aquifer-system compaction causes more than half of the land subsidence.

What Resource Managers Should Know About Land 

Subsidence in the Southern Chesapeake Bay Region

The U.S. Geological Survey is cooperating with Federal, State, and local government 

agencies to study and better understand the problem of land subsidence in the southern Chesapeake Bay region. An emphasis is placed on the vulnerable Hampton Roads communities 

adjacent to tidal waters of the Chesapeake Bay and Atlantic Ocean. The goal of the cooperative 

effort is to provide resource managers, planners, and regulators with the knowledge they need 

to make informed decisions.

Planning for Increased Flood Risks

Land subsidence can increase flooding risk, as has been seen in the Houston-Galveston 

area and the Santa Clara Valley. How land subsidence may increase flood risk in southern 

Chesapeake Bay region, either along the coasts or inland, is not currently well understood. The 

community of Franklin (fig. 2), where land has subsided and groundwater levels have decreased 

steeply, experienced extreme flooding along the Blackwater River in 1999 and 2006 (fig. 5). 

Were these flooding events made worse by land subsidence? It seems likely, but more data and 

analysis are needed to understand the link between land subsidence and the inland flooding 

near Franklin and coastal flooding in other Hampton Roads communities. Measurement and 

mapping could link subsidence to flood inundation and be used in models to forecast flooding 

potential under different scenarios.

Resource managers in the Hampton Roads area, for example, have begun planning for sealevel rise and associated flood effects (McFarlane and Walberg, 2010, 2011; McFarlane, 2012). 

Much of the expected relative sea-level rise is unavoidable, and shoreline communities will 

have to adapt. But an important component of relative sea-level rise, land subsidence, probably 

could be prevented or reduced in the future if groundwater pumping strategies were changed.

Preventing Land Subsidence

Future land subsidence caused by aquifer-system compaction can be reduced or stopped 

by changing water-use practices. Because aquifer-system compaction appears to be the primary 

cause of land subsidence in the southern Chesapeake Bay region, reducing compaction can 

potentially reduce land subsidence and associated flood risks. In the Houston-Galveston area 

and the Santa Clara Valley, resource managers have successfully decreased land subsidence by 

moving groundwater pumping away from the coast, reducing groundwater withdrawal rates, 

and increasing aquifer recharge (Galloway and others, 1999). The small contribution to land 

20 
subsidence from glacial isostatic adjustment in the southern Chesapeake Bay region—perhaps 

about 1 mm/yr (Engelhart and others, 2009)—cannot be prevented. This natural glacial isostatic 

adjustment of the Earth’s crust will diminish with time, but at a glacial or geologic pace.

Information Needed to Understand Land Subsidence and Sea-Level Rise

Although the spatial and temporal details of land subsidence have important consequences 

to flooding and sea-level rise, the details are not yet well understood in the southern Chesapeake Bay region. Land subsidence varies with location and changes over time, so additional 

monitoring is needed to better understand these aspects of land subsidence. Particularly along 

coastlines and in low-lying areas already subject to flooding, it is important to collect data that 

can improve our understanding of the mechanisms causing land subsidence. Such knowledge 

can inform long-term infrastructure investments and focus management efforts on the most 

sensitive areas.

Although aquifer-system compaction is shown to be a major cause of land subsidence 

in the region, it has been directly measured in only two locations and no extensometer data 

have been collected since 1995. More data and analyses are needed to provide a foundation of 

knowledge that can guide resource management decisions. The lack of extensometer data for 

nearly the past 20 years is a large data gap that hinders our understanding of recent aquifersystem compaction. Detailed measurements of aquifer-system compaction, such as the older 

extensometer data from Franklin and Suffolk, provide critical information needed to calibrate 

computer models of land subsidence. Ongoing collection of data is needed to maintain and 

improve models. Data describing long-term accumulation of land subsidence, best measured by 

surveying elevations at existing stations such as those used by Holdahl and Morrison (1974), 

are also useful for calibrating computer models. Obtaining multiple types of data, including 

airborne or satellite InSAR data, allows different aspects of land subsidence to be seen and 

better understood.

With appropriate data, maps showing subsidence rates over time in the southern 

Chesapeake Bay region can be constructed. Such maps would contain valuable information 

for planners and would also be useful for constructing and calibrating a subsidence simulation 

model. The model could then be used to predict future land subsidence and to evaluate alternative management scenarios.

Need for Improved Understanding of Land Subsidence in the Region

Scientific understanding of land subsidence is critical for making informed decisions about 

public investments and management of land and water resources in the southern Chesapeake 

Bay region. Many valuable resources, including developed urban centers, coastal marsh and 

wetland ecosystems, historic sites, and military facilities, are at risk of increased flooding due to 

land subsidence.

With scientific data as a foundation, basic research on land subsidence and application of 

that research can improve our understanding of land subsidence and its effect on flooding risks. 

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. We hope that this report will contribute to public awareness of and appreciation 

for current scientific opinion on the problem of land subsidence in the southern Chesapeake 

Bay region and provide useful guidance to land- and water-resource managers. Building a 

strong foundation of scientific understanding can help resource managers make better decisions 

and help build public confidence in actions taken by managers to address the problem.

 21
References Cited

Bawden, G.W., Johnson, M.R., Kasmarek, M.C., Brandt, Justin, 

and Middleton, C.S., 2012, Investigation of land subsidence 

in the Houston-Galveston region of Texas by using the global 

positioning system and interferometric synthetic aperture 

radar, 1993–2000: U.S. Geological Survey Scientific Investigations Report 2012–5211, 88 p., accessed July 19, 2013, at 

http://pubs.usgs.gov/sir/2012/5211/.

Bindoff, N.L, Willebrand, Jürgen, Artale, Vicenzo, Cazenave, 

Anny, Gregory, J.M., Gulev, Sergey, Hanawa, Kimio, Le 

Quéré, Corrine, Levitus, Sydney, Nojiri, Yukihiro, Shum, 

C.K., Talley, L.D., and Unnikrishnan, A.S., 2007, Observations—Oceanic climate change and sea level, chap. 5 of

Solomon, Susan, Qin, Dahe, Manning, Martin, Chen, Zhenlin, Marquis, Melinda, Averyt, Kristen, Tignor, M.M.B., and 

Miller, H.L., Jr., eds., Climate change 2007—The physical 

science basis, Contribution of Working Group I to the fourth 

assessment report of the Intergovernmental Panel on Climate 

Change: New York, Cambridge University Press, p. 385–432, 

accessed April 2013, at http://www.ipcc.ch/pdf/assessmentreport/ar4/wg1/ar4-wg1-chapter5.pdf.

Boon, J.D., Brubaker, J.M., and Forrest, D.M., 2010, Chesapeake Bay land subsidence and sea level change—An evaluation of past and present trends and future outlook: Virginia 

Institute of Marine Science Special Report 425 in Applied 

Marine Science and Ocean Engineering, 41 p. plus appendixes, accessed July 19, 2013, at http://web.vims.edu/GreyLit/

VIMS/sramsoe425.pdf.

Cahoon, D.R., Reed, D.J., Kolker, A.S., Brinson, M.M., Stevenson, J.C., Riggs, Stanley, Christian, Robert, Reyes, Enrique, 

Voss, Christine, and Kunz, David, 2009, Coastal wetland 

sustainability, chap. 4 of Titus, J.G., Anderson, K.E., Cahoon, 

D.R., Gesch, D.B., Gill, S.K., Gutierrez, B.T., Thieler, E.R., 

and Williams, S.J., eds., Coastal sensitivity to sea-level 

rise—A focus on the mid-Atlantic region, A report by the 

U.S. Climate Change Science Program and the Subcommittee 

on Global Change Research: Washington, D.C., U.S. Environmental Protection Agency U.S. Climate Change Science 

Program Synthesis and Assessment Product 4.1, p. 57–72.

Chesapeake Bay Program, 2011, State of the Chesapeake Bay 

program—Summary report to the Chesapeake Executive 

Council: Annapolis, Maryland, Chesapeake Bay Program, 10 

p., accessed March 11, 2013, at http://www.chesapeakebay.

net/.

Engelhart, S.E., and Horton, B.P., 2012, Holocene sea level 

database for the Atlantic Coast of the United States: Quaternary Science Reviews, v. 54, p. 12–25.

Engelhart, S.E., Horton, B.P., Douglas, B.C., Peltier, W.R., and 

Törnqvist, T.E., 2009, Spatial variability of late Holocene 

and 20th century sea-level rise along the Atlantic Coast of the 

United States: Geology, v. 37, no. 12, p. 1115–1118.

Erwin, R.M., Brinker, D.F., Watts, B.D., Costanzo, G.R., and 

Morton, D.D., 2011, Islands at bay—Rising seas, eroding 

islands, and waterbird habitat loss in Chesapeake Bay, USA: 

Journal of Coastal Conservation, v. 15, p. 51–60.

Federal Emergency Management Agency, 2002, Flood insurance study of Franklin, Virginia, community 510060 (revised 

September 4, 2002): Federal Emergency Management 

Agency, 16 p.

Galloway, D.L., and Hoffmann, Jörn, 2007, The application 

of satellite differential SAR interferometry-derived ground 

displacements in hydrogeology: Hydrogeology Journal, 

v. 15, no. 1, p. 133–154.

Galloway, D.L., Jones, D.R., and Ingebritsen, S.E., eds., 

1999, Land subsidence in the United States: U.S. Geological Survey Circular 1182, 177 p., accessed July 19, 2013, at 

http://pubs.usgs.gov/circ/circ1182/.

Gutierrez, B.T., Williams, S.J., and Thieler, E.R., 2009, Ocean 

coasts, chap. 3 of Titus J.G., Anderson, K.E., Cahoon, D.R., 

Gesch, D.B., Gill, S.K., Gutierrez, B.T., Thieler, E.R., and 

Williams, S.J., eds., Coastal sensitivity to sea-level rise—

A focus on the mid-Atlantic region, A report by the U.S. 

Climate Change Science Program and the Subcommittee 

on Global Change Research: Washington, D.C., U.S. Environmental Protection Agency U.S. Climate Change Science 

Program Synthesis and Assessment Product 4.1, p. 43–56.

Heywood, C.E., and Pope, J.P., 2009, Simulation of groundwater flow in the Coastal Plain aquifer system of Virginia: 

U.S. Geological Survey Scientific Investigations Report 

2009–5039, 115 p., accessed July 19, 2013, at http://pubs.

usgs.gov/sir/2009/5039/.

Holdahl, S.R., and Morrison, N.L., 1974, Regional investigations of vertical crustal movements in the U.S., using precise 

relevelings and mareograph data: Tectonophysics, v. 23, no. 

4, p. 373–390.

Kirwan, M.L., and Guntenspergen, G.R., 2012, Feedbacks 

between inundation, root production, and shoot growth in a 

rapidly submerging brackish marsh: Journal of Ecology, v. 

100, no. 3, p. 764–770.

Kirwan, M.L., Langley, J.A., Guntenspergen, G.R., and Megonigal, J.P., 2012, The impact of sea-level rise on organic 

matter decay rates in Chesapeake Bay brackish tidal marshes: 

Biogeosciences Discussions, v. 9, no. 10, p. 14689–14708.

Konikow, L.F., and Neuzil, C.E., 2007, A method to estimate groundwater depletion from confining layers: Water 

Resources Research, v. 43, no. 7, W07417, 15 p.

Mace, R.E., 2011, Peer review of Virginia’s groundwater 

management program: Virginia Department of Environmental 

Quality final report, December, 19 p.

McFarland, E.R., and Bruce, T.S., 2006, The Virginia Coastal 

Plain hydrogeologic framework: U.S. Geological Survey Professional Paper 1731, 118 p., 25 pls., accessed July 19, 2013, 

at http://pubs.water.usgs.gov/pp1731/.

22 
McFarlane, B.J., 2012, Climate change in Hampton Roads—

Phase III—Sea level rise in Hampton Roads, Virginia: Chesapeake, Virginia, Hampton Roads Planning District Commission report PEP12–06, July, 102 p. plus maps, accessed July 

19, 2013, at http://www.hrpdcva.gov/uploads/docs/HRPDC_

ClimateChangeReport2012_Full_Reduced.pdf.

McFarlane, B.J., and Walberg, E.J., 2010, Climate change in 

Hampton Roads—Impacts and stakeholder involvement: 

Chesapeake, Virginia, Hampton Roads Planning District 

Commission report PEP10–02, February, 43 p., accessed July 

19, 2013, at http://www.hrpdcva.gov/uploads/docs/Climate_

Change_Final_Report_All.pdf.

McFarlane, B.J., and Walberg, E.J., 2011, Climate change in 

Hampton Roads—Phase II—Storm surge vulnerability and 

public outreach: Chesapeake, Virginia, Hampton Roads 

Planning District Commission report PEP12–06, June, 79 p., 

accessed July 19, 2013, at http://www.hrpdcva.gov/uploads/

docs/HRPDC_ClimateChange2010_FINAL.pdf.

Morris, J.T., Sundareshwar, P.V., Nietch, C.T., Kjerfve, Björn, 

and Cahoon, D.R., 2002, Responses of coastal wetlands to 

rising sea level: Ecology, v. 83, no. 10, p. 2869–2877.

National Geodetic Survey, 2013, IGS08 geodetic CORS positional antennae reference point (ARP) [GRS80 ellipsoid] 

computed velocities: National Oceanic and Atmospheric 

Administration, [March 2], accessed March 3, 2013, at ftp://

cors.ngs.noaa.gov/cors/coord/coord_08/igs08_geo.comp.txt.

Poland, J.F., ed., 1984, Guidebook to studies of land subsidence 

due to ground-water withdrawal: United Nations Educational, 

Scientific, and Cultural Organization, 305 p. plus appendixes. 

(Also available at http://wwwrcamnl.wr.usgs.gov/rgws/

Unesco/PDF-Chapters/Guidebook.pdf.)

Pope, J.P., 2002, Characterization and modeling of land subsidence due to groundwater withdrawals from the confined 

aquifers of the Virginia Coastal Plain: Virginia Polytechnic 

Institute M.S. thesis, 153 p.

Pope, J.P., and Burbey, T.J., 2004, Multiple-aquifer characterization from single borehole extensometer records: Ground 

Water, v. 42, no. 1, p. 45–58.

Powars, D.S., and Bruce, T.S., 1999, The effects of the Chesapeake Bay impact crater on the geological framework and 

correlation of hydrogeologic units of the lower York-James 

Peninsula, Virginia, U.S. Geological Survey Professional 

Paper 1612, 82 p.

Pritchard, M.E., 2006, InSAR, a tool for measuring Earth’s surface deformation: Physics Today, v. 59, no. 7, July, p. 68–69.

Raucoules, D., Bourgine, B., de Michele, M., Le Cozannet, 

G., Closset, L., Bremmer, C., Veldkamp, H., Tragheim, D., 

Bateson, L., Crosetto, M., Agudo, M., and Engdahl, M., 

2009, Validation and intercomparison of persistent scatterers 

interferometry—PSIC4 project results: Journal of Applied 

Geophysics, v. 68, no. 3, p. 335–347.

Sallenger, A.H., Doran, K.S., and Howd, P.A., 2012, Hotspot 

of accelerated sea-level rise on the Atlantic Coast of North 

America: Nature Climate Change, v. 2, no. 12, p. 884–888.

Saunders, Stephen, Easley, Tom, and Spencer, Theo, 2010, 

Virginia special places in peril—Jamestown, Chincoteague, 

and Shenandoah threatened by climate disruption: Louisville, 

Colorado, The Rocky Mountain Climate Organization and 

New York, New York, Natural Resources Defense Council, 

41 p.

Sella, G.F., Stein, Seth, Dixon, T.H., Craymer, Michael, James, 

T.S., Mazzotti, Stephane, and Dokka, R.K., 2007, Observation of glacial isostatic adjustment in “stable” North America 

with GPS: Geophysical Research Letters, v. 34, no. 2, 

L02306, 6 p.

Snay, R.A., and Soler, Tomás, 2008, Continuously operating 

reference station (CORS)—History, applications, and future 

enhancements: Journal of Surveying Engineering, v. 134, 

no. 4, November 1, p. 95–104.

Sneed, Michelle, Stork, S.V., and Ikehara, M.E., 2002, Detection and measurement of land subsidence using global positioning system and interferometric synthetic aperture radar, 

Coachella Valley, California, 1998–2000: U.S. Geological 

Survey Water-Resources Investigations Report 02–4239, 29 

p. (Also available at http://pubs.usgs.gov/wri/wri024239/.)

Stork, S.V., and Sneed, Michelle, 2002, Houston-Galveston 

Bay area, Texas, from space—A new tool for mapping land 

subsidence: U.S. Geological Survey Fact Sheet 2002–110, 

6 p., http://pubs.usgs.gov/fs/fs-110-02/.

U.S. Census Bureau, 2010, Virginia–2010—Population and 

housing unit counts: U.S. Census Bureau 2010 Census of 

Population and Housing CPH–2–48, accessed April, 2013, at 

http://www.census.gov/prod/cen2010/cph-2-48.pdf.

Zervas, Chris, 2009, Sea level variations of the United States, 

1854–2006: National Oceanic and Atmospheric Administration Technical Report NOS CO–OPS 053, 76 p. plus appendixes, accessed July 19, 2013, at http://www.co-ops.nos.noaa.

gov/publications/Tech_rpt_53.pdf.

 23
A barge transporting chemicals is pushed to port by tugboat along the 

Elizabeth River in Norfolk, Virginia. Photograph by The’ N. Pham, The VirginianPilot, February 2013, used with permission.

24 

To obtain more 

Information about land subsidence and water 

resources in Virginia, visit 

http://va.water.usgs.gov/ 

or contact:

Director 

U.S. Geological Survey 

Virginia Water Science Center 

1730 East Parham Road 

Richmond, VA 23228
Prepared by the Pembroke Publishing Service Center.

For more information concerning this report, contact:

Director

U.S. Geological Survey

Virginia Water Science Center

1730 East Parham Road

Richmond, VA 23228

or visit our Web site at:

http://va.water.usgs.gov
Eggleston and Pope—Land Subsidence and Relative Sea-Level Rise in the Southern Chesapeake Bay Region—Circular 1392

Printed on recycled paper

ISSN 1067–084X (print)

ISSN 2330–5703 (online)

http://dx.doi.org/10.3133/cir1392