2023:607 - Salmon Weir Pedestrian Bridge, Gaol Road, University Road, Galway, Galway

A programme of archaeological monitoring took place of the construction of a new pedestrian and cycle bridge located c. 24m from the existing Salmon Weir Bridge (downstream), Galway City. The east side of the development is partially located within the historic town of Galway (GA094-100–) and in the vicinity of an unclassified watermill (GA094-101–) and a Franciscan Friary (GA094-102–). The project was the subject of an Archaeological, Architectural and Cultural Heritage Assessment undertaken by Faith Bailey and Ross Waters of IAC Ltd. as part of an Environmental Report commissioned by Galway City Council[1].

The new pedestrian and cycle bridge is comprised of a low-level three-span bridge, which crosses three separate watercourses. The span arrangement traverses over Persse’s Distillery River, the lower River Corrib and Friar’s River, approximately 13m, 54m and 18m in length respectively. Foundations were constructed along Gaol Road and Newtownsmith and bridge abutments were situated on the embankments of Persse’s Distillery River and Friar’s River. Utility diversions and other associated excavation works were also carried out.

Work began in May 2022 at the Gaol Road side of the river Corrib. Excavations were carried out here to facilitate the construction of a series of mini-piles (450mm diameter) and a ground beam. The works were carried out between the line of an existing low-level modern stone wall that formed the boundary between the area containing Persse’s Distillery River and the public realm surrounding the cathedral (which was subsequently removed) and the deep canal wall defining the western side of the Persse’s Distillery River. The river, also referred to as a mill race, was constructed sometime between 1838 and 1875 (it is not depicted on the First Edition Ordnance Survey Map but appears on the Second Edition). The construction of the mill race resulted in the embanking and reclamation of the west side of the river Corrib.

The stratigraphy comprised topsoil and sod overlying a deep layer of rubble and fill material resulting from embanking material to facilitate the mill race. This material extended to an overall depth of roughly 2.5m to bedrock. Excavations along the canal wall were carried out with due care and the wall was retained in situ. The inner face of Persse’s Distillery Canal/Mill race extended to a depth of 1.7m where a plinth was visible at roughly 6m OD. Nothing of archaeological significance was noted at this location.

Access to the Persse’s Distillery River embankment was established via a temporary bridge following removal of vegetation. Removal of courses of the abutment walls including sections of the stone revetments on the western bank of the river was required at this location. Excavation works were carried out here to facilitate a ground-bearing reinforced concrete abutment with the base of the abutment taken to rock level at approximately 2.5m OD.

Consistent with the Gaol Road area, the stratigraphy comprised vegetation, topsoil and sod overlying a deep layer of rubble and fill material resulting from embanking material to facilitate the mill race extending to bedrock. Nothing of archaeological significance was noted at this location.

The eastern side of the proposed development area is formed by the canal known as Friar’s River, and a narrow portion of land that separates the canal from the river channel itself, which is referred to as Friar’s River embankment. The canal is depicted on the 1838 OS map and by the time of the second edition further development is noted and the canal is depicted as dividing into two branches c. 10m to the south of the proposed development, one mill race to feed a corn mill and the other mill race leads to a malt house and distillery south of O’Brien’s Bridge. The canal occupies a much higher elevation than the bed of the river Corrib and is defined to the east by a roughly coursed masonry wall. Access to facilitate construction on the Friar’s River abutment was provided from Newtownsmith using a temporary bridge spanning Friar’s River supported on the existing quay walls, which resulted in the removal of a section of existing wall alongside Newtownsmith. The narrow-grassed embankment to the west of Friar’s River is constructed from stone, with a steeper and overgrown revetment forming the eastern bank of the river Corrib.

The stratigraphy on Friar’s River embankment comprised topsoil and sod over a compact layer of rubble and clay with a layer of impermeable clay or ‘puddle’ clay on the canal side, which sealed the rear of the canal wall. Nothing of archaeological significance was noted here.

Like the Gaol Road side a series of mini piles (450mm diameter) and a ground beam approximately 1m wide x 1.5m deep was constructed along the line of the existing stone wall on the west side of Newtownsmith. A section of walling here was removed.

Several re-used medieval or later medieval stones were used in the construction of the canal wall (Jim Higgins, Galway Co. Council, pers. comm.), possibly from the adjacent ecclesiastical site. These stones were identified by Mr. Higgins and the author and marked with paint to ensure they could be separated from the other removed stones and retained for cataloguing and eventual storage in an agreed facility.

The stratigraphy along Newtownsmith was consistent throughout with tarmac or pavement overlying roadfill and a mixed deposit of rubble and loose clays. Several preexisting services ran along the road and below the footpath.

A short section of wall was identified on the 23 May 2022 in the section face of a trench being excavated to facilitate the concrete pad for the temporary bridge at Newtownsmith.

The wall was located at ITM 529619/725512 (central coordinate) and was observed 120mm below modern ground level (5.916m OD). The wall comprises 4 courses of cut stone ranging in size from 500mm in width X 250mm in height to smaller roughly worked stones measuring 300mm X 150mm on average. The wall was unbonded with a slight batter evident. It continued to a maximum depth of 250mm at the limit of excavation for the trench. It was not possible to ascertain the width of the wall as it continued into the section face. The wall was located roughly 1.5m east of the modern canal bank wall.

After discussion with the client and the clients’ representatives on site it was agreed that no further works would be carried out and that the width of the trench was sufficient to pour concrete to facilitate the pad for the temporary bridge. No further works were carried out prior to consultation with the relevant authorities. There was a level of urgency to agreeing appropriate archaeological mitigation relating to the wall as the canal bank wall to the east had been undermined and the trench was experiencing flooding. The contractor was concerned for health and safety reasons with leaving the trench open for an extended period. For health and safety reasons it was not feasible to enter the trench due to the depth and the potential for collapse. Prior to filling the trench, the wall was photographed as wholly as possible to record it. The wall was covered by a layer of sand, geotextile and plastic and preserved in situ. After filling the trench no further impact will occur.

During excavation works further north for the ground beam the remains of a subsurface old canal wall was identified (presumably a continuation of the wall observed and described above). Excavations for the pile foundation pad for the new pedestrian and cycle bridge began on the 24 May 2022. A section of trench measuring roughly 11m was excavated. The wall was found to continue north extending to a total observed distance of 17.5m and tapered towards the existing canal bank wall towards the northern end of the trench.

The work was carried out from south to north. The wall was of a similar construction to the wall in the temporary bridge trench. It has been disturbed in parts by tree planting and a brick-lined culvert.

It was anticipated that there would be sufficient width to facilitate the sleeves for the pile foundations and the ground beam. The existing line of wall visible in the trench was surveyed photogrammetrically. A scaled 3D orthographical record was prepared of the extant remains. After recording and 3D photogrammetric recording, excavations further north (where it was thought there would be a continuation of the wall) revealed that the wall was no longer extant, having likely been removed during construction of the extant canal bank wall. The wall was covered in a layer of sand and geotextile and retained in situ.

Given the length of the wall and its alignment roughly parallel to the existing canal bank wall it is thought to likely represent either an earlier iteration of the canal or represents an inner wall of a double-skinned canal wall and as such is likely to date to the early 1800s. A comparison between the 1838 1^st edition Map and the later 25“ map appears to show a slight discrepancy between the wall along Newtownsmith. It may be the case that the wall was realigned at some point post 1838.

Nothing further of archaeological significance was note during monitoring.

[1] Salmon Weir Pedestrian and Cycle Bridge Environmental Report, 2020. Arup for Galway City Council.