Quantifying Rapid Changes in Coastal Topography using Modern Mapping Techniques and Geographic Information System

Abstract

Innovative methodology based on a combination of real-time kinematic Global Positioning System (RTK-GPS), light detection and ranging (lidar), and open-source Geographic Information System (GIS) was developed to gain a better understanding of rapid changes in coastal topography. Improved spatial interpolation techniques were implemented to produce detailed topographic surfaces from lidar and RTK-GPS data. The methodology is demonstrated for two North Carolina areas: Jockey's Ridge State Park and Bald Head Island. The Jockey's Ridge study quantifies recent dune movement and identifies areas of elevation loss and rapid horizontal migration that threaten existing infrastructure. The Bald Head Island study examines pre- and post-nourishment beach evolution. The dynamics of beach topography, its geometric properties, and estimates of both eroded and deposited sand volumes were determined by combining lidar elevation data (1997–2000) with quarterly RTK-GPS measurements. Spatio-temporal analysis confirms the relative stability of the central ‘pivot point’ beach section and reveals that the beach changed its shape from convex west of the pivot point to concave east of the pivot point during the period of 1997 to 1998 and reversed shapes during year 2000. The pivot point also divides the beach into two sections that exhibit markedly different responses to nourishment. Although the entire length of nourished beach retreated, the analysis reveals that in the western section, all nourished sand off-shore was lost, whereas in the eastern section, significant sand volume was pushed up onto the beach, creating potential for recovery.