Monteath & Powys were approached by the Department of Industry & Environment to complete a Mean High Water Mark determination along the coastline forming the eastern boundary of Lot 7317, DP1151822. Being a very steep and high cliff line with no safe access to the water line, Monteath & Powys were engaged to provide an alternative solution to conventional survey methods.
Upon reviewing the site location, it became immediately clear that physically accessing the site would not be possible and a remote sensing solution would be required. Monteath & Powys drew on existing experience with aerial photogrammetry, laser scanning and point cloud data modelling to complete this project. Additional site constraints, including the proximity to the Beecroft Peninsula Weapons Range and HMAS Albatross, further complicated the project.
After developing a proposed method in consultation with Crown Lands, approval was sought from the Office of the Surveyor General in accordance with Clause 16 of the Regulations to allow the use of remote sensing methods.
The final solution was to use a drone to capture over 4,000 images of the 1.2km long coastline and use complex meshing to build a high-resolution 3D surface model from which the Mean High Water line could be extracted.
The purpose of this survey is for an Aboriginal Land Claim. Monteath & Powys were engaged to determine the MHWM boundary only, with the remainder of the boundaries currently being surveyed by Crown Lands.
Ensuring an accurate representation of the MHWM was critical to this survey with both horizontal and vertical accuracies being paramount, it is important to remember that when reconstructing a 3D model such as this, three additional degrees of freedom exist being rotation of the model in Pitch, Roll and Yaw from the vertical (gravity) axis. Due to the height of the cliff which is about 40 – 50 metres, a small rotation could easily result in a significant shift in the horizontal position of the boundary, such rotation would also result in an incorrect Mean High Water shape being modelled as the plane cut by the MHWM RL provided would not be the true plane.
Carefully considered geometry of aerial control was required to ensure that both co-ordination and rotation of the model could be managed.
The end result allowed an accurate Mean High Water Mark to be calculated and shown on the plan of survey. This would not be possible using traditional survey techniques.