Project Details

• Latest Report:Administrative Report 23-02-01 (2 MB)
• Latest Data:Elevation Trends
• Project Staff:Thomas Ulizio
• Andrew Staley
• Heather Quinn

Background

Decades of groundwater withdrawals from unconsolidated, confined (artesian) coastal plain aquifers in Maryland have resulted in significant drawdown of groundwater levels. Water levels have declined in some aquifers to more than 170 feet below sea level (Staley and others, 2019). Projected increases in withdrawals to supply a growing population will result in additional drawdown. Withdrawing water from a confined aquifer reduces the hydrostatic pressure head in the pumped aquifer and in the adjacent confining layers (clay and silt). Reduction of hydrostatic pressure in the aquifer system resulting from the drawdown increases the load on the sediment which may lead to compaction and land subsidence. In the mid-Atlantic region, land subsidence ranging from 1.5 to 3.7 millimeters per year has occurred in the Franklin and Suffolk area of Virginia (lower Chesapeake Bay region) and is attributed to groundwater withdrawals from the Potomac Group aquifer system in Virginia (the equivalent of the Patapsco and Patuxent aquifer systems in Maryland) (Davis, 1987; Eggleston and Pope, 2013). While not likely to cause major engineering problems, land subsidence related to groundwater withdrawals could exacerbate the problem of tidal flooding caused by future sea-level rise in low-lying areas. Permanent reduction in reservoir capacity by irreversible compaction of sediments may also occur.

Regional network for measuring land subsidence

Starting in 1994, the Maryland State Highway Administration Division of Plats and Surveys began GPS surveys in Anne Arundel County at 3d rod marks at the Arnold Water Treatment Plant (ARNO) and the Broad Creek Water Treatment Plant (BROA), and a 3d mark embedded in a concrete structure at the Crofton Meadows Water Treatment Plant (CROF). Yearly GPS surveys were undertaken by Maryland State Highway personnel until 2016 when the GPS observations were conducted as a joint effort between the Maryland Geological Survey and the National Geodetic Survey (NOAA).

Starting in 2019, MGS joined a multi-agency effort to isolate vertical land motion (vlm) attributed to human activities (groundwater withdrawals) from long-term geologic signals due to glacial cycles and deep Earth processes. The group is utilizing yearly static GNSS measurements to determine vlm over a 5-year period. This effort encompasses the entire Chesapeake Bay region, from the Tidewater region of Southeast Virginia to the Northern Chesapeake and Delaware. In total, approximately 60 survey marks are being monitored every October for 2019-2023.