Infrastructure Delivery

Dec 13, 2016

Medieval cities and towns were invariably situated on coasts, estuaries or rivers. This was for the very good reasons of water supply, sanitation, transport and often power supply for mills, etcetera. The downside of this location was the vulnerability of the towns to flooding. There are numerous records of disastrous floods in these towns over the centuries. Historically, local populations got on with their lives – homes were rebuilt, bridges replaced. In recent times, the impacts of serious floods are no longer accepted by society.

In Ireland, over the last 15 years, significant flood relief schemes have been constructed for the towns of Clonmel, Ennis, Kilkenny, Waterford, Fermoy, Mallow, Carlow and Carrickon- Suir. These towns all have significant archaeological and cultural heritage, dating back to medieval times and beyond. Delivering large infrastructural projects through the centres of these towns has presented challenges for designers and contractors alike. Designers need to ensure that the finished scheme will integrate with the existing archaeological and cultural built heritage while still meeting the design standards of the project. This does not always mean replicating the existing construction materials and finishes. Sometimes, integration is best achieved by producing a modern design to contrast with the existing built heritage. Take for example the new bridge constructed over a flood relief channel in the medieval area of Oldbridge in Clonmel in comparison to the historic Old Bridge which has been retained.  During construction, the challenges have been to respect the potential for buried archaeology as well as to protect the extant archaeological built environment. In Bandon, County Cork, the design of the flood relief scheme includes lowering the river bed by up to 1.8m. This will require an underpinning of the piers and abutments of the old five arch bridge crossing the Bandon River.

The bridge is listed as a national monument in archaeological terms. Archaeological investigations discovered timber posts, termed “starlings”, along the abutments and piers of the bridge. These may have been placed as part of the temporary works for the construction of the bridge in the early 1700s or they may have been used for scour protection as three arches of the bridge and the northern abutment are founded on gravels. There is also a possibility that the timber may have been recovered from a previous timber bridge destroyed by a flood in the late 1600s.

Removing the posts as part of an archaeological contract in advance of the main contract was not an option, due to the risk of scouring undermining the bridge piers before the underpins could be constructed. The construction of the underpins will, therefore, require close coordination between the archaeology team and the contractor. The posts are to be removed over short lengths to allow the excavation for and construction of 1m wide concrete pins to proceed. This will ensure that only a short section of the bridge supports will be vulnerable to scour in the event that a flood event occurrs during the construction programme. The work will be slow and methodical but will ensure that any existing archaeological artefacts can be recovered and recorded while maintaining the stability of the 300-year-old bridge. The new concrete underpins will be faced with stone to match the existing stonework of the piers with much of the stone expected to be recovered from other parts of the site.