SEACLIFF EROSION ANALYSIS USING 3D LASER SCANNING

Significant erosion and collapse of unstable seacliffs on the western coast of the United States threatens existing development and public safety. Continual time-series mapping of the seacliffs and beaches using terrestrial laser san (TLS) provides improved understanding and quantification of the processes responsible for cliff erosion, in addition to the reworking and transport of the failed material. Combining this data with wave, tidal, and climate data provides unique insights into sea cliff morphology.

Newly developed methodologies enable geo-referencing of scan data in dynamic environments where standard survey control is difficult to establish. This methodology utilizes real-time kinematic GPS systems, internal scanner sensors, and recent automated algorithms. In addition, studies were completed to determine optimal scanning parameters including scan setup spacing, resolution, and distance from cliff. This efficient method has been successfully implemented for time series mapping of seacliffs in San Diego County, California since 2007 and in Oregon since 2010, and will be continued for long-term change analysis. Sites showing more significant change (e.g. collapse) were surveyed on a more frequent basis to monitor sediment dispersal from the failed material. Classification systems were also developed to analyze the frequency of large versus small failures and the amount of wave contact to the failure mass.

The detailed resolution (both spatially and temporally) of these datasets show unique insights to observe coastal morphological processes at multiple scales. For example, unconsolidated failed material was observed to quickly be reworked into the beach upon wave contact. Feedback mechanisms were also observed where large boulders from failed sections of sea cliffs stabilized talus deposits and prevented exposure of the cliff base, preventing wave undercutting. However, such a feedback causes failures due to wave undercutting and notching to migrate laterally and might explain the long-term linear retreat of the seacliffs that minimizes the development of embayments and promontories.