National Assessment of Coastal Vulnerability to Sea-Level Rise: Preliminary Results for the U.S. Atlantic Coast

Coastal Vulnerability Index (CVI)

The coastal vulnerability index (CVI) presented here is similar to that used by Gornitz et al. (1994), as well as to the sensitivity index employed by Shaw et al. (1998). The index allows the six physical variables to be related in a quantifiable manner. This method yields numerical data that cannot be directly equated with particular physical effects. It does, however, highlight those regions where the various effects of sea-level rise may be the greatest.

VERY LOW
• variable: 1
• Geomorphylogy: rocky, cliffed coasts, Fiords, Fiards
• coastal slope (%):>.2;
• relative sea-level change (mm/yr): <1.8
• shoreline erosion/accretion (m/yr): >2.0
• mean tide change (m): >6.0
• mean waveheight (m): <.55

LOW
• variable: 2
• Geomorphylogy: (medium cliffs, indented coasts)
• coastal slope (%): .2 - .07;
• relative sea-level change (mm/yr): -1.8 - 2.5
• shoreline erosion/accretion (m/yr): 1.0 - 2.0
• mean tide change (m): 4.1 - 6.0
• mean waveheight (m): .55 - .85

MODERATE
• variable: 3
• Geomorphylogy: Low cliffs, glacial drift, alluvial plains
• coastal slope (%): .07 - .04;
• relative sea-level change (mm/yr): 2.5 - 2.95
• shoreline erosion/accretion (m/yr): -1.0 - +1.0 (stable)
• mean tide change (m): 2.0 - 4.0
• mean waveheight (m): .85 - 1.05

HIGH
• variable: 4
• Geomorphylogy: Cobble beaches, estuary, lagoon
• coastal slope (%): 0.4 - .025
• relative sea-level change (mm/yr): 2.95 - 3.16
• shoreline erosion/accretion (m/yr): -1.1 - 2.0 Erosion
• mean tide change (m): 1.0 - 1.9
• mean waveheight (m): 1.05 - 1.25

VERY HIGH
• variable: 5
• Geomorphylogy: Barrier beaches, sand beaches, salt marsh, mud flats, deltas, mangrove, coral reefs
• coastal slope (%): <.025
• relative sea-level change (mm/yr): >3.16
• shoreline erosion/accretion (m/yr): <-2.0
• mean tide change (m): <1.0
• mean waveheight (m): >1.25

Once each section of coastline is assigned a risk value based on each specific data variable, the coastal vulnerability index is calculated as the square root of the geometric mean, or the square root of the product of the ranked variables divided by the total number of variables as

where,

• a = geomorphology
• b = coastal slope
• c = relative sea-level rise rate
• d = shoreline erosion/accretion rate
• e = mean tide range
• f = mean wave height