2002:1530 - RIVER BOYNE, Stagrennan, Meath

The harbour master at Drogheda Port requested maintenance dredging of the Boyne Estuary from the bar inland to the west along the navigable channel. This was to remove the build-up of estuarine silts that was causing docking problems for the deeper draught ships trying to gain access to the development at Tom Roe’s Point, Co. Louth. It was required that the works be monitored. This was primarily owing to the large quantities of archaeological material recovered during the monitoring of capital dredging in this part of the Boyne in April 2000.

The work was carried out by a single vessel of suction-hopper type, the MV Lesse. Suction hopper dredging involves a large, self-propelled, open-hold ship, which acts like a giant vacuum cleaner on the seabed, sucking up loose material. The dredger has a dredge pump and drag-head along its side. The dredge pump and drag-head effectively act as the vacuum components of the vacuum cleaner. The dredge pump sucks material from the seabed through the drag-head and then through its pump, emptying the material into the open hold, or hopper, of the ship.

Monitoring of trailer suction-hopper dredgers is carried out through the periodic inspection of the drag-head. The drag-head is the only area of the dredger to impinge on the seabed. It has a large surface area, owing to the presence of a protective grid on the base of the drag-head. This is designed to prevent large stones and other heavy material being sucked into the dredge pump and damaging it. The drag-head works by moving over the seabed, sucking up loose material. Any hard material it sucks up becomes stuck on the protective grid, and the subsequent loss of suction through the drag-head necessitates its recovery to the surface for removal. The remnants recovered from the drag-head allow the monitoring archaeologist to ascertain whether the material is archaeological. Some dredgers, the MV Lesse included, also feature gridded screens over the hold through which the dredged material is pumped. These can also be checked by the archaeologist for any large objects that may have become lodged.

Monitoring took place from 6 to 17 September, when dredging operations were completed. The work of the dredger in the river was restricted to the hours around high tide, and it generally dredged only one load of material on each high tide before moving offshore to the dumping ground. The dredger generally also dredged one load at the estuary bar on each tide. The archaeologist was aboard during all works in the river. Although not required by Dúchas, several shifts on the bar were also monitored. During monitoring, the start and finish coordinates of each dredge cycle were recorded so that any material in the drag-head could be assigned to a given zone. Eighteen shifts were monitored, with three spent on standby owing to bad weather and a single shift not covered because of health-and-safety factors. A log was kept by the archaeologist, and a report sheet was filled out for each shift.

The vast majority of dredging undertaken was in the area around the container quay at Tom Roe’s Point (c. NGR 311570 275800), although several runs were also made farther downstream, near the abandoned fishmeal factory (c. NGR 314600 277100).

Nothing of an archaeological nature was recovered during the monitoring. Several pieces of wood were retrieved but were either clearly modern or lacked any clear evidence of human working. Most of the material removed from the drag-head was modern domestic and industrial rubbish.

3 Canal Place, Tralee, Co. Kerry