AN ARCHAEOLOGICAL INVESTIGATION OF THE YEALM HEAD, SOUTH-EAST OF PLYMOUTH BREAKWATER

Plymouth Sound has an extensive history of maritime activity; there have been hundreds of disasters and accidents whereby the Sound is of significant archaeological interest. Following discussions with Peter Holt of 3H Consulting, a dissertation project was created regarding the wreck of the Rover which, due to strong winds, sunk on December 12th 1804 on the rocks near Yealm Head, on the eastern side of Plymouth Sound. The dissertation project aimed to find all the man-made objects within a specific survey area. The area in question has never been investigated, which therefore gives full justification for a full geophysical survey to be untaken. A high resolution MBES survey carried out on the 27th March giving an image never seen before of the sea floor. The DTM was able to give accurate depth information as well as provide bathymetry which has helped characterise the sea floor as shallow, smooth and fine sediment in the North East of the survey area, changing to a submerged deeper riverbed when heading South West. The backscatter data also helped to classify the sea floor, but the final mosaic created lacked clarity. The project was unable to detect any non-iron objects through a visual inspection. A magnetometer survey was conducted on the 3rd July 2014. The data was filtered and a range of anomalies were selected for analysis and further processing. The results indicated four or five possible targets. The targets were presented alongside the processed multibeam data on a number of different charts. A minimum detectable target (MDT) was also created for the entire survey area showing that when using a 15m line space, a fish altitude based on multibeam depth (reduced to LAT) and minimum anomaly of 5nT, in the most shallow point of the survey area a target needs to be at least 213.174kg to be identified by the G-882 magnetometer used in the survey. At the deepest point, a target must be at least 2857.65kg to be identified. The targets identified are considered sufficient to warrant further investigation by divers, ROV’s or other remote sensing methods