IHBC Yearbook 2017

26 Y E A R B O O K 2 0 1 7 raise uncomfortable dilemmas. Open to the prevailing south- westerlies, Cornwall’s coast is particularly exposed, compelling successive generations to build and maintain sea-facing structures, which often provided scant protection. From the mid-18th century, advances in civil engineering led to the building of more audacious structures in locations where safe navigation was previously impossible. However, while some marine infrastructure attracts high levels of interest, it is the more modest structures – breakwaters, quays, locks, sea marks and other minor features – which are vital to a harbour’s functionality and contribute most to their coherent preservation as historic settings. Harbour infrastructure is easily overlooked, poorly understood and vulnerable to unsympathetic alteration. Historic harbours can make a major contribution to regional tourism and the viability of coastal communities, but in this context the infrastructure is valued principally for its picturesque qualities. Historic breakwaters are some of the most remarkable survivors but their significance is rarely well articulated, partly because they cannot be understood simply by transferring our knowledge of masonry structures on land. Mainly built in shallow water, facing the heaviest oncoming waves, these structures are exposed to the random and dynamic force of breaking waves as the tide ebbs and floods. Their height must exceed the maximum tidal range plus an allowance for expected extreme wave heights. As their height increases, so must their thickness in cross-section to ensure stability. Therefore, monumental masonry structures are required even in small Cornish harbours, which typically have a tidal range of 6–8 metres. Some repeatedly failed during construction, while others were frequently rebuilt after great storms, evidencing centuries of occupation and endeavour. Elsewhere, lack of maintenance has led to complete loss, as at Trevaunce where the former harbour is marked only by blocks of dressed stone littering the beach. With predictions of a worsening wave climate and increased storminess, maritime infrastructure is firmly in the front line of climate change. The scale of damage experienced in 2014 is nothing new – great storms have occurred throughout history. But following the collapse in coastal trading and fishing in the early 20th century, many tidal harbours in the south west went into severe decline. Hindered by remoteness and lack of funding, most have nevertheless survived relatively intact. Many exposed harbours evolved from simple cove landing places with a degree of natural protection: Mullion, Mousehole and Marazion are all in the lee of islands. Others were protected by reefs, headlands or sandbars. Masonry structures began to appear in Britain around the 14th and 15th centuries. These were short simple structures founded in shallow water. Mousehole, the principal port of Mount’s Bay until the 16th century, was the first in Cornwall to acquire a protective quay around 1393. This situation largely persisted until the mid-18th and 19th centuries when many harbours were extended to accommodate enlarged fishing fleets or to service ventures such as mining. Until this time, harbours were vernacular structures. The earliest builders used stone in its natural state with wide joints through which wave energy and internal air pressure could safely dissipate. The integrity of later work, roughly coursed but unbonded, depended on the frictional interlocking of roughly shaped stones. This evolved into the well-jointed roughly squared masonry now thought typical of early 18th-century work. Modestly sized stones were laid vertically to optimise their mass against wave uplift and as more mass was added above the stones became locked together more tightly below. Quarrying and transport improvements from the mid-18th century meant that larger units of the densest stone were used, sometimes up to four feet in depth and laid flat to form tightly jointed outer skins infilled with rubble. These structures were still highly permeable, allowing the tide to rise through the loose hearting, pushing air outwards through interstices, and on the ebb, permitting sea water to drain freely. The blocks were left roughly dressed to optimise frictional resistance to waves. Mortar was used sparingly, often to prevent displacement of the top ‘pitching’ which was vulnerable to down-falling waves. This method was used in 1837 to construct a second breakwater at Mousehole, fully enclosing the harbour. Despite its exposure to southerly gales, the entire evolutionary sequence of building described above survives on the inner face of the South Quay at Mousehole (page 27). The mid-18th century saw a move towards highly engineered structures. John Smeaton advised on many harbour improvement works (but caution is required in assuming the extent to which sophisticated developments in offshore lighthouse design influenced more modest harbour works). Until the 1880s Mousehole had the largest fishing fleet in Mount’s Bay, and the harbour was often full. In 1868, a government grant was obtained by the harbour improvement commissioners to double its size. The 1837 quay was demolished Two-minute time lapse sequence showing the destruction of the Portreath Harbour forward observation hut (1890) by storm waves in 2014 (Photo: Colin Higgs, www.portreathstudio.com )