Coastal cliff geometry derived from structure-from-motion photogrammetry at Stara Baška, Krk Island, Croatia

Abstract

The aim of this study was to examine the capability of structure-from-motion photogrammetry in defining the geometry of cliffs and undercuts in rocks of complex geomorphology. A case site was chosen along pocket beaches near the village of Stara Baška on the Adriatic Sea island of Krk, Gulf of Kvarner, Croatia, where cliff erosion of 5 m in breccias was identified by comparison of aerial photographs from 1960 and 2004. The 3D point cloud was derived from approx. 800 photos taken on 9 January 2014 by a single camera from various elevations and angles, and processed using the online software ReCap (Autodesk). Data acquisition was found to be quick and the method easy to implement. The difference between the georeferenced 3D cloud points and an RTK-GPS survey was 7 cm, i.e. within the limits of RTK-GPS precision. Quantifying the spatial variation in undercut geometries revealed that the deepest and largest (17 m 3 ) undercut was in the south-eastern sector of the beach. Reconstructing the detailed geomorphology of this 3.8-m-deep undercut convincingly demonstrates the high efficiency of the method. Such assessments of spatiotemporal changes in undercut and overhang volumes can prove useful for evaluations of cliff erosion risk. Coupled with the low cost and relatively simple application, this is evidently an attractive technique for meaningful geotechnical and coastal engineering monitoring in the future on the island of Krk and, for that matter, also on other Adriatic islands and in similar settings worldwide.

Image-based surface reconstruction in geomorphometry – merits, limits and developments

“…Up to 90 000 points m −2 enabled the identification of bedrock faulting. Ružić et al (2014) produced surface models of coastal cliffs to test the abilities of SfM photogrammetry in undercuts and complex morphologies.…”

Rekonstrukcija recentnih morfoloških promjena žala uz pomoć metode ponovljene fotografije – primjer žala Zogon na otoku Hvaru (Srednji Jadran)

“…One of the newest methods for tracking changes in morphology of beach and its surrounding is the SfM photogrammetry that started to be used in Croatia (e.g. Pikelj et al, 2014;Ruži et al, 2014;Pikelj et al, 2015;Tomini, 2017). Today, different methods are often combined and complemented.…”

“…Even if there are different kind of beaches along the eastern Adriatic coast (see e.g. Pikelj, Jurai, 2013;Marriner et al, 2014;Ruži et al, 2014), a large number of beaches is formed in proluvial material of small valleys and gullies (ravines) (Jurai et al, 2009;Faivre et al, 2011;Ruži et al, 2011). The occasional streams bring the material out of the drainage basin and create fans in which the beaches are formed in the contact with the sea.…”

Coastal erosion and instability phenomena at Stara Baška, Krk Island, Croatia

“…Numerical simulations shows the wave (H S =2.4m) energy dissipation for various sea levels on the embayed beach. Numerical simulations results are presented on 3D point clouds delivered from image set using Structure-from-Motion photogrammetry (RUŽIĆ et al 2014;2015). generally increase cliff and beach erosion.…”