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Home > Explore! > Coastal Marine Geology > Impacts > Methodology

Impacts of Future Sea Level Rise on the Coastal Floodplain

Methodology

Compile required data coverages

gridded topography of study area
Figure 2		 MGS acquired 2004 LIDAR topographic data from the NOAA Coastal Services Center. The data was received in gridded, bare-earth, 4-m averaged bin resolution. The LIDAR data has a vertical RMSE of 0.067 m. The flight was completed on May 5-6, 2004. Gridded LIDAR data for the study area is shown in Figure 2.

MGS acquired high quality true color (24-bit) 1-foot resolution aerial orthophotographs of the study area from the Maine Office of GIS (MEGIS). The original aerial photographs were flown on May 19, 2003.

All data coverages were compiled within ESRI ArcMap® for data display and analysis.

Project a static 2-ft rise in sea level and its impacts on the study area.

Water levels for the study area were determined using a simplified tide calculator created by MGS for converting between different datums (Dickson, 2005). Using this data, we then calculated the area (m2) of different marsh types within the study area for existing conditions. This was then done for 1, 2, and 3-ft sea level rise scenarios.

It is important to point out the assumptions associated with this project, which include:

  1. Different marsh areas correspond with different water levels. We assumed that low marsh, dominated by Spartina alterniflora, existed between the limits of open water (0 m NAVD) and the mean high water (MHW) line (calculated to be 1.2 m NAVD). High marsh, dominated by Spartina patens, was assumed to exist within the area between MHW and the highest annual tide (HAT, 1.8 m NAVD; see Table 1). In general, the determined elevations corresponded very well with aerial interpretation of marsh vegetation. Existing areas of open water, low marsh, high marsh, and upland (above highest annual tide) were determined (see Figure 2). Afterwards, we simulated a static 1, 2, and 3-ft rise in sea level using the LIDAR topography and subsequent changes in sea level, mean high water, and highest annual tide.
  2. Marshes are able to keep up with sea level rise. We assumed that both high marsh and low marsh will be able to overtake and colonize existing land to the limits designated by the increases in tidal elevations after 1, 2, and 3 ft of sea level rise. This assumes that sedimentation rates will be able to keep up with sea level rise.
  3. Marsh transgression is not impeded by existing developed property. We assumed that marsh transgression will continue even on currently developed properties.
  4. Sea level rise is static. We assumed that existing topography (from the 2004 LIDAR) will not change in response to a rising sea level.

Contents   Introduction   Methodology   Results   Discussion   Findings and Recommendations   Conclusions   References

Last updated on April 21, 2006