KIRK MICHAEL

Central Alliance have been contracted by SURVEYAR to conduct drone-based surveys on a section of coastline at Kirk Michael on the Isle of Man, for the Isle of Man government, to assess the rate at which the sea cliffs are eroding as part of their “National Strategy on Sea Defences, Flooding and Coastal Erosion”. This stretch of coastline is being surveyed due to the proximity of housing estates and properties in Kirk Michael. Scheduled surveys have been carried out in July and October 2024, and April 2025 continuing from a series of aerial surveys starting in 2019, with an emergency survey carried out in December 2024 to assess any changes after Storm Darrah.

The Isle of Man is primarily made up of a thick pile of sedimentary rocks, dating from the Ordovician period, more commonly known as Manx Slates or the Manx Group, with smaller areas of later sedimentary and extrusive igneous strata. With older strata dating from the Caledonian and Acadian orogenies. A suite of dykes of the Ordovician to Silurian age have intruded into the rocks of the Manx group and are well exposed along the rocky shores around Kirk Michael.

Along the coastline making up the work site can be found many sedimentary rocks. The Kirk Michael Member is composed of sands and shells of Turritella communis, there are also fine glacial clays found around Glen Wyllin, at the southern end of the site.

Whilst working on site we were informed by a local dog walker, that his mother remembers the area from the 1940s and that there was a Corn Mill and more fields where we were stood (on the beach). As can be seen in the images below, the top image shows a red + at the end of the road on the left, with the corresponding cross on the right showing where that location is now, with the bottom image showing the location of the Corn Mill and its corresponding location today. On the left is a map dated 1885-1900, with the right-hand side being an up-to-date Google Maps image. As can be seen, the cliff/coastline has been eroded and receded at quite a rate since the early 1900s.

On the visits conducted by Central Alliance, two flights were conducted from the beach, with two further flights conducted away from the beach, but still covering the sea cliff, this was to help with georeferencing, so it wasn’t just a linear site. The two flights away from the beach, also helped capture the areas above the cliff.

Using a DJI Mavic 3E multispectral drone platform, a 1.2km stretch of the beach and sea cliff were surveyed. Each visit captured approximately 5700 images. To ensure each image was accurately located, the drone uses RTK (Real-Time Kinematic – a technique that uses global navigation satellite system (GNSS) to provide precise location data) location to get CM accuracy. They were also pre-processed using PPK – Post-Process Kinematic, which uses a base station to determine an accurate position after data collection, using algorithms to determine positions. To confirm these locations are correct, Ground Control Points (GCPs) were also used (the positions of which are shown below, represented by the green crosses). These consisted of 60cm wide disks, that can be seen by the drone. The GCPs were surveyed in using a Trimble Catalyst, which ensured that they were accurate to at least 3CMs. The GCPs were placed at various points across the site, capturing the range of elevations.

Once the surveys had been completed, the images were processed; firstly using ESRIs Drone2Map, creating an orthographic image, a digital surface model (shown below), and a pointcloud that can be compared to previous surveys using CloudCompare.

This comparison is then used to determine where deformation has occurred between the surveys, the red areas show the deposited material, whereas the green areas show where material has been removed/eroded by physical processes.