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Coastal Vulnerability Assessment of War in the Pacific National Historical Park to Sea-Level Rise
USGS Open-File Report 2005-1056

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 GATE 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

Geologic Variables

Figure 3. Photos of geomorphic features within the Asan Beach Unit of War in the Pacific NHP.
Figure 3. Photos of geomorphic features within the Asan Beach Unit of War in the Pacific NHP. Click on figure for larger image.
Figure 4. Photos of geomorphic features within the Agat Unit of War in the Pacific NHP.
Figure 4. Photos of geomorphic features within the Agat Unit of War in the Pacific NHP. Click on figure for larger image.

The geomorphology variable expresses the relative erodibility of different landform types (Table 1). These data were derived using the 2002-2003 IKONOS imagery provided by the Pacific Islands GIS Project and NOAA/NOS (http://www.csc.noaa.gov/islandsgis/resources.html). In addition, field visits were made within accessible locations of the park to verify the geomorphologic classification (Figure 3 A-B and Figure 4 A-C). War in the Pacific NHP consists of geomorphology types, that include high vulnerability rubble to rocky shoreline skirted by fringing reef and very high vulnerability sand beaches with fringing reef (Figure 5).

Figure 5. Coastal geomorphology for War in the Pacific NHP.
Figure 5. Coastal geomorphology for War in the Pacific NHP. Click on figure for larger image.
Figure 6. Shoreline change rates for War in the Pacific NHP.
Figure 6. Shoreline change rates for War in the Pacific NHP. Click on figure for larger image.

Shoreline erosion and accretion rates for War in the Pacific NHP were calculated using digitized shorelines from 1966 and 2002/2003 (Table 2). Shoreline rates of change (m/yr) were calculated at 50 m intervals (transects) along the coast using Digital Shoreline Analysis System (DSAS) software (http://woodshole.er.usgs.gov/project-pages/dsas/) to derive the rate of shoreline change. The change rates for each transect within each grid cell were averaged to determine the shoreline change value used here, with positive numbers indicating accretion and negative numbers indicating erosion. Shoreline change rates within the park are all in the moderate vulnerability category, which is between -1 m/yr and +1 m/yr. The rocky portions of the shoreline have not changed since 1966, There has been some erosion along Asan Beach and other sandy areas, although rates still lie within +/- 1 m/yr (Figure 6).

Figure 7. Regional coastal slope for War in the Pacific NHP.
Figure 7. Regional coastal slope for War in the Pacific NHP. Click on figure for larger image.

Regional coastal slope is an indication of the relative vulnerability to inundation and the potential rapidity of shoreline retreat because low-sloping coastal regions should retreat faster than steeper regions (Pilkey and Davis, 1987). The regional slope of the coastal zone was calculated from a grid of topographic and bathymetric elevations extending 2 km landward and seaward of the shoreline. Elevation data were obtained from the National Geophysical Data Center (NGDC) as gridded topographic and bathymetric elevations at 0.1-meter vertical resolution for 1-minute grid cells. These data were supplemented with DEM data from NOAA's Biogeography Program and SHOALS (Scanning Hydrographic Operational Airborne Lidar Survey) data (Table 2). Regional coastal slopes for War in the Pacific National Historical Park fall within the very low to very high vulnerability category (< 4.55% - > 14.7%) (Figure 7).

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