Bluff Stability Analysis Using 15 Years of Lidar Data

Geoscience Consultants, LLC (Geoscience) was contracted by McSweeney Engineers to examine some of the historical and physical changes to the bluff shoreline at Magnolia Plantation along the Ashley River. The goal was to help assess engineering design options for bluff stabilization. The four primary questions included:

1. Stability of the Upper Portion of the Embarkment,

2. Stability of the Lower Portion of the Embarkment Below the Waterline,

3. Historical Shoreline Change, and

4. Potential Future Shoreline Change.

To help answer these questions Geoscience leveraged about 15 years (2006/7-2020) of lidar data to assess elevation trends along the bluff shoreline in concert with the lithology and morphology of the bluff. There were three high density data sets collected at the site from 2006/7, 2017, and 2020. 

Because there are many potential ‘objects’ above the ground that are recorded by the laser pulses it was important to understand what they were reflected from. The base data was provided with a ‘best estimate’ of whether the point hit ground or something else. For this work looking for small changes in a steep shoreline under significant vegetation the data were re-analyzed/reclassified by Geoscience for the specific purpose of the project. Additionally, the lidar were all shifted/adjusted vertically to correspond to the 2020 data set. These processing steps produced three consistent data sets that were used to examine the slope and shoreline trends during the past 15 years as well as serve as a high-resolution topographic map for design and planning of future shoreline protection systems.

Example of the complex lidar returns from dense vegetation and steep bluffs at the sits.