The Barmouth Viaduct is a Grade II* listed structure which carries the single track of the Dovey Junction to Pwllheli line and footway over the Mawddach estuary. It is in a marine environment where timber below the high tide mark is at most risk in Use Class 5 and all timber above in Use Class 3.2, permanently exposed to the risk of wetting. The structure consists of a timber trestle viaduct of 113 timber spans with 5 steel spans over the deep-water channel. It is of historic importance and is the longest functioning timber viaduct in the UK and is a vital link on the Cambrian line. However, the structure is ageing and under attack from a number of biological agents. Within the intertidal zone, the structure is at risk of attack by shipworm. Above the intertidal zone, the structure is permanently at risk of attack by wood decaying fungi. The structure is undergoing a £20 million refit with much of the work focussing on the renewal of timber that has been attacked by biological agents. The combination of an ageing infrastructure and stressed maintenance budgets provides the impetus to develop innovative methods to support the asset management plan of the structure. Understanding the performance of materials and their rates of deterioration may inform design choices. Moreover, understanding the impact of climate change and local environmental factors and how this can change the distribution of marine borers and affect the risk of decay can also support the long-term asset management of the viaduct.

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