2011:103 - GLANAGOW TO RAFFEEN, Cork

Monitoring took place of all foreshore, intertidal and underwater disturbances associated with preparatory works and the installation process for the Glanagow to Raffeen Subsea 220kV Cable Project. Three works components required monitoring: foreshore trenching, pre-lay grapnel run (PLGR) and cable-embedding operations.

Monitoring of the excavation of four cable trenches was undertaken at the two landfall sites, located at Glanagow (Whitegate) and Raffeen (Ringaskiddy). The cable trenches were excavated using a long-reach tracked-machine excavator and extended from the low-water mark to the upper foreshore at the transition joint locations. Each cable trench measured 1m in width by 1.25m in depth. The work was undertaken at low water and each trench was cut in three stages, allowing the seaward point of each trench to be dug first, followed by the middle and upper foreshore locations. The monitoring process did not reveal any material, deposits or structures of archaeological significance: the upper levels of each trench comprised redeposited beach material or a sterile silty sand; the lower reaches were composed of a silty clay deposit that was archaeologically sterile.

Monitoring of the PLGR was carried out on completion of the foreshore trenching. The PLGR was undertaken to identify and remove any potential obstacles prior to commencement of the cable-laying and embedding operation. The PLGR was undertaken using the Port of Cork Authority’s multi-cat vessel the Dennis Murphy. A range of modern debris was recovered that included tractor tyres and a series of iron/steel cable lengths. No material of archaeological significance was encountered as part of the PLGR.

A programme of monitoring for all seabed disturbances associated with the cable-embedding operation was devised. A self-propelled multi-purpose barge, the Victor, was used as a dive platform for the on-site cable installation contractors, JD Contractor A/S. The cable-embedding process employed a self-propelled (water-powered) sled carrying a series of jetting heads that were used to cut each of the seabed trenches to a depth of 2m+ within the navigation channel and 1.5m+ outside the channel. The sled was positioned and monitored by a commercial diver on the seabed, the diver being present to ensure correct burial depth and to facilitate removal of any seabed obstacles encountered during the sled’s operation.

Monitoring of the embedding process was implemented through systematic monitoring of the diver’s hat-mounted HD video feed and continual logging of sled position and kilometre position (KP) along the cable. In the event of an obstacle being encountered, the archaeologist would inspect the object via the video feed and, where deemed necessary, have the object brought on board for closer inspection, recording and assessment.

Despite the considerable archaeological potential ascribed to the seabed within Cork Harbour, only one object of archaeological potential was recovered as part of the cable-embedding operation: an isolated oak encountered at KP 2.780 on Cable 4, NGR 181022 62827. The exact nature of the timber is unclear, and its dimensions do not indicate that it formed part of the framing or planking timber associated with a timber vessel. It may, however, have formed part of the upper elements of a vessel, decking timber, etc. If this was the case, the timber has also undergone reuse at a later date. It is likely to date from the 19th or early 20th century. It was fully recorded and then redeposited on the seabed outside of the cable-embedding works at NGR 180776 63893.

The Archaeological Diving Company Ltd, Brehon House, Castlecomer, Co. Kilkenny