1999:127 - RIVER BANN, Coleraine, Derry

Management for Archaeology Underwater was contracted by DOE (NI) to carry out underwater archaeological investigations in the River Bann at Coleraine. The investigations were required to assess the threat to archaeological remains from the proposed construction of a footbridge on the northern side of the old bridge in Coleraine.

The site is directly to the north of Coleraine Bridge. It consists of two 6m2 plots where the proposed footbridge piers would be installed. The centres of these piers are 7.7m from Coleraine Bridge. The river is bordered at this point by stone walling on the Waterside (west) and the metal piles of the Bannside Wharf to the east.

The investigations required a number of underwater strategies. The river was visually inspected by divers, noting the components of the riverbed and searching for archaeological features. Given the relatively unpolluted nature of the river and the small area involved, full coverage was possible even in low visibility. Divers carried out the inspection by laying a central north-south baseline and setting a grid around the area involved. They then carried out an open-water grid search. This involves the diver moving up and down the grid within a set number of lanes, the width of which depends on the visibility. The topography of the riverbed was also noted during the inspections, as any profound anomalies would require further investigation.

Limited probing into the riverbed was carried out during the inspection by the use of a 0.5m wooden rod. This is a quick method of locating any large objects buried in the sediment.

Metal-detection was carried out using Fisher metal-detectors. In a low-visibility environment this was an added tool in assessing the man-made content of the riverbed by non-intrusive means. Again, transects were followed within the grids and the frequency of hits was noted. Metal-detection is by definition only an indicator of metal items, but it does give a glimpse of the overall density of man-made material at the different locations. In addition, it hints at buried items that may be of archaeological value. Metal artefacts, notably a large collection of prehistoric items, have been recovered from the River Bann in the past. Where possible, divers identified these metal items, although a great deal were covered in sediment and would have required extensive excavation.

As a final testing method for archaeology, two test-trenches were excavated. These were positioned north-south along the central baseline, cutting right through the centre of the grid. The trenches were 0.5m wide and c. 0.4–1m deep and were excavated using a diver-operated water dredge. The pumped material was discharged onto a sieve on the surface for examination.

Among the finds were some coins, including three British halfpennies or pennies, two definitely from the reign of George III (1760–1820). The single piece of flint found showed signs of working in antiquity. It had a subtle bulb of percussion and some striking on the opposite face. It is a piece of debitage rather than a finished artefact.

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