New Crowd Sourcing Will Contribute to Study of Land Subsidence and Sea-Level Rise in the Chesapeake Bay

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Issue: Chesapeake Bay region has the highest rate of relative sea-level rise on the Atlantic Coast of the United States. Scientists use the term relative sea-level rise to describe the change in ocean height relative to changes in land elevation.  Data indicate that vertical land motion in the form of subsidence has been responsible for more than half the relative sea-level rise measured in the Chesapeake Bay region, an area with shorelines covering over 18,500 km (~11,500 mi; Boon et al., 2010).  Land subsidence in the Chesapeake Bay region is believed to be caused by the compounding effects of groundwater withdrawals, glacial isostatic rebound, and deep geologic processes occurring in the Earth’s mantle.  As communities in the region grapple with nuisance flooding, and resource managers address the loss of coastal wetlands, it is important to understand and potentially manage land subsidence and prepare for future conditions.

Instrumentation to measure land subsidence at a site in Virginia Beach

Instrumentation to measure land subsidence at a site in Virginia Beach
(Credit: Russ Lotspeich, USGS VA/WV WSC.)

USGS Study: The purpose of the USGS-led effort is to better isolate short-term changes in land subsidence due to human activities, from long-term geologic signals due to glacial cycles and deep Earth processes. Identifying the short-term changes will provide insights into ways localities can manage and use aquifers to reduce land subsidence.

Scientists from the USGS are collaborating with NOAA National Geodetic Survey, Virginia Tech, Maryland Geological Survey, US Fish and Wildlife Service, the National Park Service, Hampton University, Virginia Institute of Marine Sciences, and the Delaware Geological Survey federal, state, and local governments to measure land-surface subsidence at the rate of a few millimeters per year in the Chesapeake Bay. 

 

Some of the innovative approaches for the study include:

  • Group of scientists embark each October, using dual-frequency GPS receivers, to collect high precision satellite observations for >72 hours at 55 geodetic benchmarks. 
  • Crowd sourcing techniques will be used to facilitate government and academic collaboration and engage with local community members and landowners.  In addition to benchmarks in public spaces, benchmarks have been installed at fire stations, healthcare facilities, commercial lots, back yards, front yards, and agricultural fields for observation.  Crowd sourced locations increase awareness of study goals and provide opportunities for interaction amongst community members and scientists.
  • The findings will be used to generate revised maps that depict the variability of land subsidence based on observing changes at 55 benchmark elevation points across the Chesapeake Bay region. The data will also improve models that predict possible effects of land subsidence and aquifer management decisions on critical wetland habitat.

 

Management Applications:

So what’s the big deal about a few millimeters of land subsidence in management decisions? 

Rates and locations of land subsidence change over time so accurate measurements and predictive tools are needed to improve the understanding of its causes. 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 (Eggleston and Pope, 2013; Wade et al., 2018).

Most scientists agree that relative sea-level in the southern Chesapeake Bay region is rising at rates upwards of 5 mm/yr.  Despite being measured in millimeters, when changes in sea-level are compounded over 80 years or even forecasted into the next century, major cities such as Washington D.C. and Baltimore, as well as the port of Norfolk, are at risk.  Results of this study will help inform resiliency plans for these cities.

Sea-level rise is also impacting important coastal habitats for migratory birds and wildlife. Of concern to coastal scientists and land managers in the Chesapeake Bay is the inability of wetlands to naturally migrate inward in response to sea-level rise. This study will generate land subsidence maps of the Chesapeake Bay region that can be used by ecological researchers at the USGS Patuxent Wildlife Research Center to develop computer models of the possible effects of land subsidence and help inform aquifer management decisions on critical wetland habitat.

The USGS has several coastal-habitat efforts to help the Chesapeake Bay Program make progress on its  goal to “Increase the resiliency of the Chesapeake Bay watershed, including its living resources, habitats, public infrastructure and communities, to withstand adverse impacts from changing environmental and climate conditions”.

Click here for more information on USGS Chesapeake Bay studies

 

References:

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

Eggleston, J. and Pope, J. (2013) Land Subsidence and Relative Sea-Level Rise in the Southern Chesapeake Bay Region. U.S. Geological Survey Circular 1392.

Wade, C. M., Cobourn, K. M., Amacher, G. S., & Hester, E. T. (2018). Policy targeting to reduce economic damages from land subsidence. Water Resources Research, 54, 4401–4416, https://doi.org/10.1029/2017WR022133.

 

For more information:

Kurt J. McCoy, kjmccoy@usgs.gov
R. Russell Lotspeich, rlotspei@usgs.gov

 

Science Summary was released September 17, 2020.

 

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