Mapping the Puget Sound Coastal Zone for Geomorphic and Ecological Assessment Using Vessel-Mounted Topographic Lidar and Multibeam Bathymetric Sonar

Vessel-mounted topographic lidar is being used to map coastal geomorphology, habitat features, and human modifications along the shores of Puget Sound in Washington State, USA. The horizontal-look angle of the mobile laser scanner provides an advantageous view of the coastal landscape, particularly for bluff-backed beaches common to the Salish Sea. High-resolution point clouds provide for the classification and extraction of metrics essential for quantitative physical characterization and assessment of nearshore ecosystem structure, process, and function. Key features such as bluff toe elevation, back-beach width, overhanging riparian vegetation, large woody debris, beach wrack, and shoreline armor have been mapped and quantified in 3D space for geospatial correlation. This information can help determine the relative need for restoration of fragmented habitat and the value for protection of intact habitat, and could be used to establish reference criteria for restoration efforts. Repeat surveys have enabled comprehensive and detailed documentation of conditions before and after restoration projects. Vessel-mounted lidar facilitates efficient monitoring and change analyses of physical features as well as the assessment the spatial and temporal effects of restoration actions, human interventions, and natural episodic events such as landslides. Multibeam sonar complements the topographic lidar with high-resolution nearshore bathymetry to provide seamless coverage across the nearshore coastal zone. Topobathymetric surface differences between sequential surveys enable the determination of sediment supply, transport, and deposition, and the development of littoral cell sediment budgets. Multibeam sonar also detects submerged aquatic vegetation and benthic habitat such as oyster beds, and enables the assessment of the interplay between terrestrial and marine processes in shaping the Puget Sound nearshore.