Coastal Vulnerability to Sea-Level Rise: A Preliminary Database for the U.S. Atlantic, Pacific, and Gulf of Mexico Coasts

This is more than double the rate of eustatic rise for the past century (Douglas, 1997; Peltier and Jiang, 1997). The prediction of coastal evolution is not straightforward. There is no standard methodology, and even the kinds of data required to make such predictions are the subject of much scientific debate.

A number of predictive approaches have been used (National Research Council, 1990), including: 1. extrapolation of historical data (for example, coastal erosion rates); 2. static inundation modeling; 3. application of a simple geometric model (for example, the Bruun Rule); 4. application of a sediment dynamics/budget model; or 5. Monte Carlo (probabilistic) simulation based on parameterized physical forcing variables. Each of these approaches, however, has its shortcomings or can be shown to be invalid for certain applications (National Research Council, 1990).

Similarly, the types of input data required vary widely, and for a given approach (for example, sediment budget), existing data may be indeterminate or may simply not exist (Klein and Nicholls, 1999). Furthermore, human manipulation of the coast in the form of beach nourishment, construction of seawalls, groins, and jetties, as well as coastal development itself, may dictate Federal, State and local priorities for coastal management without proper regard for geologic processes.

Thus, the long-term decision to renourish or otherwise engineer a coastline may be the primary determining factor in how that coastal segment evolves. Variables Affecting Coastal Vulnerability: We use here a fairly simple classification of the relative vulnerability of different U.S. coastal environments to future rises in sea-level. This approach combines the coastal system's susceptibility to change with its natural ability to adapt to changing environmental conditions, and yields a relative measure of the system's natural vulnerability to the effects of sea-level rise (Klein and Nicholls, 1999).

The vulnerability classification is based upon the relative contributions and interactions of six variables: 1. Tidal range, which contributes to inundation hazards. 2. Wave height, which is linked to inundation hazards. 3.

Coastal slope (steepness or flatness of the coastal region), which is linked to the susceptibility of a coast to inundation by flooding and to the rapidity of shoreline retreat. 4. Shoreline erosion rates, which indicate how the given section of shoreline has been eroding. 5. Geomorphology, which indicates the relative erodibility of a given section of shoreline. 6.

Historical rates of relative sea-level rise, which correspond to how the global (eustatic) sea-level rise and local tectonic processes (land motion such as uplift or subsidence) have affected a section of shoreline. The input data for this database of coastal vulnerability have been assembled using the original, and sometimes variable, horizontal resolution, which then was resampled to a 3-minute grid cell. A data set for each risk variable is then linked to each grid point.

For mapping purposes, data stored in the 3-minute grid is transferred to a 1:2,000,000 vector shoreline with each segment of shoreline lying within a single grid cell. [Summary provided by the USGS.]