Skip past header information
USGS Logo with link to USGS Web page
National Park Service Logo and link to Web site
Coastal Vulnerability Assessment of Dry Tortugas National Park (DRTO) to Sea-Level Rise
USGS Open-File Report 2004-1416

Map of Coastal Vulnerability

Skip past contents informationTable of Contents link to Title Page Link to Abstract Page Link to Introduction Page Link to Data Ranking Page Link to Dry Tortugas National Park Page Link to Methology Page Link to Geologic Variables Page Link to Physical Process Variables Page Link to Calculating the Vulnerability Index Page Link to Results Page Link to Discussion Page Link to Conclusions Page Link to References Page

Data Ranking System

Table 1 shows the six variables described in the Introduction, which include both quantitative and qualitative information. The five quantitative variables are assigned a vulnerability ranking based on their actual values, whereas the non-numerical geomorphology variable is ranked qualitatively according to the relative resistance of a given landform to erosion. Shorelines with erosion/accretion rates between -1.0 and +1.0 m/yr are ranked as being of moderate vulnerability in terms of that particular variable. Increasingly higher erosion or accretion rates are ranked as correspondingly higher or lower vulnerability. Regional coastal slopes range from very high vulnerability, <0.3 percent, to very low vulnerability at values >1.2 percent. The rate of relative sea-level change is ranked using the modern rate of eustatic rise (1.8 mm/yr) as very low vulnerability. Since this is a global or "background" rate common to all shorelines, the sea-level rise ranking reflects primarily local to regional isostatic or tectonic adjustment. Mean wave height contributions to vulnerability range from very low (<0.55 m) to very high (>1.25 m). Tidal range is ranked such that microtidal (<1 m) coasts are very high vulnerability and macrotidal (>6 m) coasts are very low vulnerability.

Table 1: Ranges for Vulnerability Ranking of Variables on the U.S. Atlantic and Gulf Coast.

   Variables Very Low
Very High
GEOMORPHOLOGY Rocky cliffed coasts, Fjords Medium cliffs, Indented coasts Low cliffs, Glacial drift, Alluvial plains Cobble Beaches, Estuary, Lagoon Barrier beaches, Sand beaches, Salt marsh, Mud flats, Deltas, Mangrove, Coral reefs
SHORELINE EROSION/ACCRETION (m/yr) > 2.0 1.0 - 2.0
-1.0 - 1.0
-2.0 - -1.0
< -2.0
COASTAL SLOPE (%) > 1.20 1.20 - 0.90
0.90 - 0.60
0.60 - 0.30
< 0.30
1.8 - 2.5
2.5 - 3.0
3.0 - 3.4
> 3.4
0.55 - 0.85
0.85 - 1.05
1.05 - 1.25
> 1.25
4.0 - 6.0
2.0 - 4.0
1.0 - 2.0
< 1.0

Skip Footer Information [an error occurred while processing this directive]