Sea-level rise (SLR) is a major climate change impact that will have a wide range of effects on coastal environments (Douglas and others., 2001; IPCC, 2007; FitzGerald and others, 2008). During the 21st century, the rate of SLR is projected to be several times higher than that measured over the past century (Meehl and others, 2007; Rahmstorf, 2007; figure SL1). Recent projections suggest that sea level may be ~0.6 to 1.5 m higher than present by 2100 (Rahmstorf, 2007; Horton and others, 2008; Jevrejeva and others, 2010), and ~2 m higher only under extreme warming scenarios (Pfeffer and others, 2008; Vermeer and Rahmstorf, 2009; Grinsted and others, 2010). There will also be substantial global and regional variations in relative sea-level change – both positive and negative – due to a range of geophysical, gravitational, and oceanographic processes (Peltier, 1994; Bamber and others, 2009; Hu and others, 2009; Milne and others, 2009; Mitrovica and others, 2009; Yin and others, 2009).
Over the last few decades, a number of studies have examined tide gauge data to identify long-term sea-level rise trends along the coast of the U.S. (Hicks, 1983; Zervas, 2001; 2009, Gornitz and Lebedeff, 1987; Gornitz and Seeber, 1990; Braatz and Aubrey, 1987; Emery and Aubrey, 1991; Nicholls and Leatherman, 1996; Douglas, 2001). Long-term relative sea-level observations along portions of the Atlantic and Gulf coasts exceed the global average rate while rates along the U.S. West coast and Alaska are more variable. In some locations in the Pacific Northwest and Alaska, sea-level is falling relative to the land surface (Zervas, 2009). The high rates of relative sea-level rise observed in the mid-Atlantic and Gulf coast regions have been attributed to subsidence of the land surface due to two principal factors. At a regional scale, subsidence has been attributed mainly to lingering glacio-isostatic adjustments of the earth’s crust in response to the melting of the Laurentide ice sheet, (Gornitz and Lebedeff, 1987; Braatz and Aubrey, 1987; Emery and Aubrey, 1991; Nicholls and Leatherman, 1996; Peltier, 2001; Douglas, 2005). On a local scale, the compaction of sediments due to freshwater or hydrocarbon withdrawal from coastal aquifers is also thought to contribute to subsidence (Davis 1987; Kearney and Stevenson 1991; see review in Nicholls and Leatherman 1996; Morton and Bernier, 2010). Regions where a fall in relative sea-level has been observed, like portions of the Pacific Northwest and Alaska, are generally located in areas where tectonic activity has led to the uplift of the land surface over time (Zervas, 2009).