THE APPLICATION OF LIDAR IN MONITORING BARRIER ISLAND VOLUMETRIC CHANGE AND SHORELINE POSITION AT THE GULF ISLANDS NATIONAL SEASHORE, MS

The U.S. Geological Survey (USGS) used the Experimental Advanced Airborne Research Lidar (EAARL) to collect topographic data for ecological monitoring, storm-event assessment, habitat mapping, and evaluating geomorphic change on the Gulf Islands National Seashore, MS. In this study, 1-m, 5-m, and 10-m digital elevation models (DEMs) were created from EAARL data to assess and monitor morphologic change at Gulf Islands National Seashore, MS. Lidar data were collected in September 2005, June 2007, and September 2008 to capture “normal” island conditions and storm impacts that occurred during those times. Morphologic change was determined between each of the acquisition periods by calculating net volumetric change per unit area (m) and identifying shoreline-position variation as well.

Each survey did not cover the same extent of the barrier island; the net volumetric change was normalized by dividing by unit area. Results from the volumetric-change analysis showed that the type of features to be evaluated need to be considered. A lower-resolution DEM could be used to characterize the whole barrier island, whereas a detailed 1-m-resolution DEM would be useful in evaluating features on the beach. To provide satisfactory characterization of a particular study area, determine the resolution at which maximum variability occurs and select the higher resolution occurring before that level.

Datum-referenced shorelines were extracted for each study area in 2005, 2007, and 2008. The study sites have a constant value shoreline of 0-m North American Vertical Datum of 1988 (NAVD88) Geoid03 that has been established. Not all years of collection covered the full barrier island and as such the shoreline areas were absent in those sections.

The shoreline-position analysis showed the Mississippi barrier islands are elongating and becoming narrower on both the Gulf and Mississippi sides in response to shoreline erosion by longshore and cross-shore sediment transport. Even though the shoreline perimeter was eroding on many of the barrier islands, the volumetric-change analysis measured an interior buildup of sediment during the time of collection. Further insight into the processes that determine the “long-term” barrier-island modification will increase with additional lidar collection, with samples occurring under “normal” island conditions.