For the past five years, the HRPDC’s work plan has focused on quantifying and evaluating the impacts of sea level rise in Hampton Roads. Since land subsidence - the compaction and settling of ground surface area - can increase flooding, alter coastal ecosystems and damage infrastructure, it is important for regional planners to understand why, where and how fast land subsidence is occurring. In Hampton Roads land subsidence is estimated at 1.1 to 4.8mm/year, which is over half of the measured relative sea level rise for the region.
HRPDC staff recently collaborated with the U.S. Geological Survey (USGS) to evaluate all types of land subsidence measurements in the region and determine why the region is sinking. This effort culminated in a USGS Circular, Land Subsidence and Relative Sea-Level Rise in the Southern Chesapeake Bay Region, released to the public December 9, 2013. Table 3 of that circular, “Observed sea-level rise and subsidence in the southern Chesapeake Bay region,” summarizes the measured rates of land subsidence from the 22 monitoring stations that have recorded data beginning in 1940. The report concludes that land subsidence in Hampton Roads is primarily a result of groundwater pumping and glacial isostatic adjustment, the flexing of the Earth’s crust in response to glacier formation and melting.
With improvements to the existing groundwater model for the Virginia Coastal Plain aquifer system, future subsidence could be evaluated; however, additional monitoring data would be needed to calibrate the model and better understand how land subsidence varies within the region.