CGS Home CSG Staff
Mapping Shorelines Using Airborne Lidar

Measuring Shoreline Change Along Bays and Oceans Using Historical Aerial Photography and Airborne Topographic Lidar Surveys

Mapping Historical Shorelines
Interpretation and Mapping
Ground Surveys

Click on images to enlarge.

Introduction and Mapping

The rectified images are brought into ArcView GIS software for digitization of the shore and vegetation lines. The shoreline is mapped ideally by tracing the boundary between wet and dry sand. Often, the wet/dry line is not distinct from the water line, and the mapped shoreline may follow the visible water line or the scarp of an erosional shoreline. The vegetation line is mapped as the seaward boundary of continuous vegetation. Large "islands" of vegetation on the beach are also mapped. All lines are mapped at an average scale of 1:3,000.

Because of tidal and meteorological changes in water levels and gently sloping bay margins, the vegetation line in places may be more reliably related to average water level than the wet/dry line. The shoreline is ideally mapped as the contact between wet and dry sand as shown here on the bay and ocean side of this spit.
Where there is no beach, the shore and vegetation lines will overlap as in this bay delta setting. Shoreline digitization in ArcView. A georectified image is easily brought into the GIS environment to be used as a background image or as a base map from which vector data can be extracted.

Shoreline Change Analysis

Shorelines from multiple years are overlain in ArcView GIS. A computer program called the Shoreline Shape and Projection Program (SSAPP) is used to calculate the rate of shoreline change alongshore. SSAPP automatically constructs baselines that follow the trend of the historical shorelines and uses a linear regression model to calculate rates of change along transects perpendicular to the base lines.

ArcView window with historical shorelines and transects generated by SSAPP.

Top of page