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Methodology for assessing coastal change using terrestrial laser scanning

  • Author(s): Olsen, Michael James
  • et al.
Abstract

Seacliff erosion dramatically alters the coastline of San Diego County through both marine and subaerial mechanisms, threatening development and public safety in the economically important coastal regions. Quantitative analysis of the seacliffs' stability assists public policy makers to determine safe and effective coastline utilization. This dissertation develops concepts, techniques, and tools drawing from multiple disciplines to provide this essential information of both seasonal and rapid-event erosion. Terrestrial Laser Scanning (TLS) produces high resolution data to accurately quantify erosion and map hazard areas. Previous work applying TLS to seacliff erosion required additional, time-consuming surveying to georeference TLS surveys, limiting their application to only localized sites. This dissertation presents new methods to georeference TLS data for efficient, quantitative regional mapping and to quantitatively understand sources of uncertainty. The determination of optimal scanning parameters of spacing, distance, and sampling ratio ensures adequate data collection to capture the complex seacliff morphology. A new, automated algorithm for alignment shows how to constrain errors to avoid detrimental misalignment propagation, advancing TLS surveying for application to map long coastal sections. These techniques provide substantial time savings over previous methods, ensure consistent results between repeat surveys, and allow simultaneous study of both small and large scale geologic processes. The creation of a rapid-response program to observe sites immediately and continually after failure shows the insights TLS can provide in conjunction with wave, tidal, and climate data in understanding geologic processes governing seacliff erosion. The TLS data also showed that minimal wave energy is required to rework failure sediment and suggests that some failure masses can act as a stabilizing force for the cliffs by securing protective talus deposits against the cliff.The development of automated GIS routines to perform statistical change analysis is also presented. These routines were applied to both cliff and beach studies to show the importance of studying both small and large scale changes to understand geologic processes. These innovative methods provide a framework for future scientists and engineers to utilize TLS in understanding complex problems by ensuring sufficient data collection, establishing accurate, georeferenced baselines, and providing tools to perform meaningful change analysis.

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