A comparison the 95% confidence intervals of the mean sea level trends obtained from NOAA's Sea Level Trends. Trends with the narrowest confidence intervals are based on the longest data sets. Trends with the widest confidence intervals are based on only 30-40 years of data. The graphs give an indication of the differing rates of vertical land motion, given that the absolute global sea level rise is believed to be 1.7-1.8 millimeters/year [Douglas, 1991].
Tide gauges around the Chesapeake Bay indicate that the relative sea level in the Bay is rising at around twice the average global rate of 1.8 mm per year. Tide gauges measure sea level changes relative to the land on which the the tide gauge rests. By itself, a tide gauge cannot tell the difference between local crustal motion and sea level changes, it is impossible to discern a sea level rise from land subsidence. In any given region, the apparent rate of rise can vary considerably from the long term global value. Geographical and temporal variations from the long-term mean value occur from a variety of causes such as interdecadal fluctuations of ocean density and circulation, continuing isostatic adjustment of the land level from the last deglaciation, subsidence due to the extraction of underground fluids, etc. The mean sea level (MSL) trends measured by tide gages are local relative MSL trends as opposed to the global sea level trend. Tide gauge measurements are made with respect to a local fixed reference level on land; therefore, if there is some long-term vertical land motion occurring at that location, the relative MSL trend measured there is a combination of the global sea level rate and the local vertical land motion.
To help tease out actual sea level rise from the apparent sea level rise we can use data from NOAA's National Geodetic Survey (NGS) which operates the Continuously Operating Reference Station (CORS) network consisting of Global Navigation Satellite System (GNSS) reference stations which provide phase and code range measurements in support of three dimensional positioning, meteorology, space weather, and geophysical applications throughout the United States, its territories, and a few foreign countries.
To see how sea level rise may affect coastal regions have a look at NOAA's Sea Level Rise Viewer. You can see the vertical slider to emulate water level rise, the resulting inundation footprint, and relative depth. Click on icons in the map to view sea level rise simulations at specific locations. Areas that are hydrologically connected to the ocean are shown in shades of blue (darker blue = greater depth) and low-lying areas, displayed in green, are hydrologically "unconnected" areas that may also flood. They are determined solely by how well the elevation data captures the area’s drainage characteristics.