Preliminary Investigation of Land Subsidence Impacts on Sea Level Change in Baltimore Inner Harbor, Maryland

A NOAA tide gauge in Baltimore Inner Harbor has monitored sea level changes since 1902 for 116 years. This gauge seats on the over semi-consolidated Cretaceous strata of Arundel clay (Kac) underlain by Patuxent sand (Kxs) facies and the Pre-Cambrian undifferentiated crystalline rock. The Patuxent sand layer is the most important confined aquifer in the Baltimore history. The shallow Arundel clay and the deep Pre-Cambrian crystalline rock can be its upper and lower confining units, respectively. It was estimated that the groundwater pumpage increased gradually from practically nothing in about 1850 to about 23 thousand-m³/day in 1900 in the Baltimore area. After this the pumpage only increased slightly to 53 thousand-m³/day until about 1915. After 1935 the pumpage increased rapidly to 142 thousand-m³/day in 1941 then decreased. Primary compaction subsidence due to groundwater withdrawal is identified from the tide gauge records in this paper while secondary compaction subsidence due to creep under constant geohistorical overburden pressure is assumed to be zero since the maximum historical overburden pressure was released by uplift of the compressible aquifer system. A GPS receiver at University of Maryland at Baltimore County (UMBC) is 12 km far from the tide gauge located in the Baltimore Inner Harbor and seats on the late Precambrian Baltimore Gabbro Complex (bgb). Tectonic subsidence of 1.57±0.52 mm/year was measured at UMBC by using the GPS UMBC. So land subsidence in the Baltimore Inner Harbor consists of tectonic subsidence and primary compaction subsidence. We find an absolute sea level rise (SLR) of 1.11 mm/year by removing tectonic subsidence of 1.57 mm/year from a relative SLR of 2.68 mm/year during 1962 to 1980 with groundwater level stability in trend. Land subsidence impact on the sea level change in the inner harbor is empirically estimated to be 1.93 mm/year during 1903 to 1920, -3.15 during 1920 to 1926, 4.13 during 1926 to 1947, 1.74 during 1947 to 1957, -1.91 during 1957 to 1962, 1.57 during 1962 to 1980, and 2.17 during 1980 to 1992, respectively.