Cutting Edge Research

Coastal Impact Study:
Nation Under Siege

Sea Level Rise

In order to accurately determine sea level rise along the US coast, base maps were constructed using United States Geological Survey - National Elevation Datasets (NED) for selected areas of interest. The NED is a seamless raster dataset of US elevations. Within the NED, the US is divided into 10 meter-by-10 meter squares, whose elevations correspond to the average elevation within a square. The NED is a compilation of elevation data from many sources, including LIDAR and USGS digital elevation models.

The Sea Level datum within the NED does not necessarily coincide with local mean sea level (MSL) along the US coastline. The elevations in the NED are based on the North American Vertical Datum, 1988 (NAVD88). The NAVD88 fixes Sea Level (zero elevation) at a particular point in Quebec, Canada. All US elevations within the NED are calculated relative to that zero point (adjusted for the curvature of the earth). For most purposes, the NAVD88 represents an acceptable standard for deciding elevations above Sea Level. Along a coastline, however, the level of the sea does not everywhere correspond to zero on the NAVD88. A correction was applied to the NED to bring it in line with actual local tidal conditions.

Once corrected sea levels were established, a flood-fill algorithm was used to determine contiguous inland access from the coastline for increased sea levels. For each area studied, the land-water edge, based on corrected sea level, was determined. The algorithm used this edge as the starting point of the flood-fill and moved inland. From each flooded point, the algorithm selected neighboring pixels that were at, or below, the corrected sea level. The algorithm continued from these neighboring points until no new points were selected.

Flood maps generated using the flood-fill algorithm were then superimposed over Google Earth images to illustrate in detail how localities will be flooded on a calm, rain-free day at high tide at various increments of sea level rise [7].

7. Maps are based on LIDAR data and USGS 10m NED. Maps are illustrative; areas in blue depict various potential inundation scenarios. Map accuracy is dependent on the accuracy of the geospatial data.

 

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Foreword
Introduction
Sea Level Rise
Visual Imaging
One Meter of Sea Level Rise... and Rising
A Lesson Learned?
Current Trends
Timeline
Fossil Fuels and Climate Change
The Power of Coal
Silver Bullet: Moratorium on Coal
Replacing Coal
The 2030 Challenge
Been There, Done That
Revisiting Katrina
Conclusions
Appendix

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