Section 9: Extracting a Shoreline from Lidar Data Historical Aerial Photography ( Provides Historical Shoreline Positions) 1930s to 1990s - Vertical Aerial Photographs Shoreline Interpretation on Photography ( Wet/Dry Line) Gulf of Mexico Matagorda Bay MHHW+0.6 m msl Geotube Landward boundary BEG-02 Beach profile QAd496Gibeaut_CCC_Jan31_2002 Lidar Digital Elevation Model (1 - m Grid) Ellipsoidal heights converted to orthometric heights (NAVD 88) using GEOID99 gravity model. Local mean sea level (MSL) correction applied. Lidar Survey Video Galveston Beach Wet/Dry Line Intensity Draped on Topography Galveston Island Profile Representative Wet/Dry Elevation 0.6 m along Upper Tx Gulf Coast MHHW Height relative to MSL (m) Distance (m) 50 upper berm crest vegetation line Why Use a Wet/Dry Elevation? Consistent with historical photography. Consistent with 2d ground GPS surveys. Lidar can measure reliably even during elevated water levels. Geomorphologically significant elevation not as susceptible to short-term erosion/depositional cycles compared to lower elevations. Hand-Smoothed Shoreline