U.S. Geological Survey
Coastal and Marine Geology
Woods Hole Field Center
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National Assessment of Coastal Vulnerability to Sea-Level Rise: Preliminary Results for the U.S. Gulf of Mexico Coast
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Coastal Vulnerability Index
The coastal vulnerability index (C.V.I.) 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 that expresses the relative vulnerability of the coast to physical changes due to sea-level rise. This method yields numerical data that cannot be equated directly with particular physical effects. It does, however, highlight those regions where the various effects of sea-level rise might be the greatest.
Table 1. Ranking of coastal vulnerability index:
VERY LOW
- variable: 1
- Geomorphylogy: rocky, cliffed coasts, Fiords, Fiards
- coast slope (%): >0.115;
- relative sea-level change (mm/yr): <1.8
- shoreline erosion/accretion (m/yr): >2.0
- mean tide change (m): >6.0
- mean waveheight (m): <0.55
LOW - variable: 2
- Geomorphylogy: (medium cliffs, indented coasts)
- coast slope (%): 0.115-0.055;
- relative sea-level change (mm/yr): 1.8-2.5
- shoreline erosion/accretion (m/yr): 1.0-2.0 (accretion)
- mean tide change (m): 4.1-6.0
- mean waveheight (m): 0.55-0.88
MODERATE
- variable: 3
- Geomorphylogy: Low cliffs, glacial drift, alluvial plains
- coast slope (%): 0.055-0.035;
- relative sea-level change (mm/yr): 2.5-3.0
- shoreline erosion/accretion (m/yr): (-1.0)-(+1.0) (stable)
- mean tide change (m): 2.0-4.0
- mean waveheight (m): 0.85-1.05
HIGH
- variable: 4
- Geomorphylogy: Cobble beaches, estuary, lagoon
- coast slope (%): 0.035-0.022
- relative sea-level change (mm/yr): 3.0-3.4
- shoreline erosion/accretion (m/yr): (-1.1)-(-2.0) Erosionv
- 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
- coast slope (%): <0.022
- relative sea-level change (mm/yr): >3.4
- 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
CVI=square root of ( (a*b*c*f*e*f) /6 ) )
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
The C.V.I. values reported here apply specifically to the U.S. Gulf of Mexico coast, but are also comparable to the values for the U.S. Atlantic coast since the data ranges for the Gulf of Mexico are categorized using overall values for both coasts. Absolute C.V.I. values given for the Pacific coast, however, (e.g., Thieler and Hammar-Klose, 2000) are not directly comparable to the data presented here. We feel this approach best describes and highlights the vulnerability for each of the different continental margin types that make up the U.S. coast.
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Introduction
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Risk Variables
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Data Ranking
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CVI
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Results
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Discussion
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Summary
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References
This report is preliminary and has not been reviewed for conformity with U.S. Geological Survey editorial standards or with the North American Stratigraphic Code. Any use of trade, product, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.
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