Three years of morphologic changes at a bowl blowout, Cape Cod, USA

Abstract

This study presents measurements of blowout topography obtained with annual terrestrial laser surveys carried out over a three-year period at a single, large bowl blowout located in the Provincelands Dunes section of Cape Cod National Seashore, in Massachusetts. The study blowout was selected because its axis is aligned with northwest winds that dominate the region, and because it was seemingly interacting with a smaller saucer blowout that had recently formed on the southern rim of the primary feature. Assuming that blowouts enlarge both horizontally and vertically in response to the wind regime, the objectives of the study were to determine both the amount of horizontal growth that the blowout experiences annually and the spatial patterns of vertical change that occur within the blowout. Changes to the blowout lobe surrounding the feature were also determined for areas with sparse enough vegetation cover to allow laser returns from the sand surface. The results show that the blowout consistently expanded outward during the three years, with the greatest expansion occurring at its southeast corner, opposite the prevailing winds. The most significant occurrence was the removal, in the first year, of the ridge that separated the two blowouts, resulting in a major horizontal shift of the southern rim of the new combined blowout. This displacement then continued at a lesser rate in subsequent years. The rim also shifted horizontally along the northwest to northeast sections of the blowout. Significant vertical loss occurred along the main axis of the blowout with the greatest loss concentrated along the southeast rim. On the lobe, there were large areas of deposition immediately downwind of the high erosion zones inside the blowout. However, there were also small erosion areas on the lobe, extending downwind from eroding sections of the rim. This study shows that: 1. blowouts can experience significant areal and volumetric changes in short periods of time; 2. significant changes may occur relatively suddenly when adjacent blowouts combine into a single feature; and 3. the sediment transport paths are highly controlled by the topography. The joining of two blowouts not only creates a new larger feature, but it also releases large amounts of sediment that are then distributed across the landscape downwind, creating a potential for major changes to a landscape over the longer term.

Evaluation of UAV LiDAR for Mapping Coastal Environments

“…Terrestrial LiDAR offers a significant improvement in the spatial resolution and accuracy of topographic data over airborne platforms. Smith et al [21] presented measurements of blowout topography obtained with annual terrestrial LiDAR surveys carried out over a three-year period. With a 10 mm total propagated positional error, they were able to measure rim displacements smaller than 1 meter.…”

“…Attributed to the nature of laser scanning, LiDAR has the ability to penetrate vegetation and report elevation below the canopy. Several studies suggested that terrestrial LiDAR provides a suitable representation of the ground surface in vegetated coastal dunes [21,22]. Although the spatial resolution of terrestrial LiDAR data is much higher than airborne data, the point density decreases considerably as the scanner-to-object distance increases.…”

Terrestrial LiDAR monitoring of coastal foredune evolution in managed and unmanaged systems

“…Frequent terrestrial LiDAR scanning (TLS) has been used recently to study beach‐dune morphodynamics and can help resolve small‐ and large‐scale dynamics, including storm response and recovery (e.g. Montreuil, ; Schubert et al ., ; Fairley et al ., ; Fabbri et al ., ; Smith et al ., ; Telling et al ., ; Brodie et al ., ).…”

Tracking Fine-Scale Structural Changes in Coastal Dune Morphology Using Kite Aerial Photography and Uncertainty-Assessed Structure-from-Motion Photogrammetry

“…To date, a variety of both remote and proximal sensing techniques have been used to answer questions about dune morphology, dynamics and change, and for the management of dune systems. For example, terrestrial laser scanning (TLS) has proven useful for quantifying coastal dune morphology [13], and repeat TLS has been used successfully to monitor the evolution of erosion features such as dune blowouts [14]. TLS has also been deployed to track erosion and predict overtopping of anthropogenic berms on the coast [15].…”