Conserving Cornish harbours
Historic harbour infrastructure is in the front line of climate change yet recent research suggests that the conservation sector is poorly engaged with this aspect of the UK’s heritage. Hilary Wyatt demonstrates the urgent need to extend understanding, promote co-operation and provide specialist guidance.
|Storm Frank, December 2015: waves break over the finger pier and Bickford-Smith Institute at the entrance to Porthleven Harbour, Cornwall (Photo: Colin Higgs, www.portreathstudio.com).|
The damage inflicted by a succession of exceptionally severe weather systems affecting the south and west coasts of the UK and Ireland in the winter of 2013–2014 exposed the vulnerability of coastal built heritage, highlighting the profound challenges that lie ahead in attempting to manage the predicted effects of climate change. A chain of Atlantic depressions generated intense wave activity. Inshore, massive ocean swells coincided with unusually high Spring tides to produce storm surges which inundated sheltered deep-water ports such as Plymouth and Cork and caused critical damage to a number of small Cornish harbours.
At St Michael’s Mount part of the historic causeway was lost. At Porthleven the timber baulks across the entrance were smashed, allowing destructive breakers to penetrate the inner harbour. At Portreath the forward observation hut was swept away in minutes. At Mullion both breakwaters were damaged and granite copings thrown into the harbour. Elsewhere parapets, slips and sea walls were shifted and undermined in successive storms.
|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).|
The Cornish coast contains some of the most popular heritage settings in the UK. Its small-scale tidal harbours continue to draw large numbers of visitors and form the mainstay of Cornwall’s tourism economy. Harbours are often viewed as timeless yet the coastal zone is a place of rapid and dynamic change. However, research suggests that the public has a low level of engagement with maritime issues. Perhaps more worryingly, a similarly low level of engagement seems to exist within the wider conservation sector. A 2014 report, ‘Ports and The Historic Environment’ (see Further Information), concluded that the relationship between Historic England and the port sector was generally weak and reactive.
There is almost no current guidance on the management of historic harbour infrastructure. One exception, the Environment Agency’s Old Waterfront Walls (see Further Information), indicates that many historic sea-facing structures are now functioning as de-facto flood defences. Historic texts by engineers such as John Smeaton, Leveson Francis Vernon-Harcourt and Thomas Stevenson are invaluable in understanding historic construction methods, but the lack of accumulated baseline knowledge reflects in a lack of specific guidance from heritage bodies on the repair and adaptation of historic harbour settings. Consequently, list descriptions and conservation area appraisals often fail to analyse the significance of harbour structures and settings with the same confidence shown in the assessment of townscape.
The overwhelming designation of marine infrastructure at Grade II excludes many structures from the Heritage at Risk register, preventing any overall evaluation of condition and future risks. Furthermore, while the Port Marine Safety Code imposes a ‘duty to maintain’, there is no equivalent duty within the principal heritage acts and destruction by natural forces falls outside the consent process. It remains unclear how these sites can be sustainably managed in the long term, or how ready the conservation sector is to participate in a debate that may challenge established conservation principles and inevitably result in the partial or total loss of coastal heritage assets.
Open to the prevailing south-westerlies, Cornwall’s coast is particularly exposed, compelling successive generations to build and maintain protective sea-facing structures. 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. Easily overlooked, and poorly understood, these features are vulnerable to unsympathetic alteration and removal.
Historic breakwaters are some of the most remarkable survivors of our built environment but their significance is rarely well articulated, partly because they cannot be understood simply by transferring our knowledge of masonry structures on land. Built in shallow water, and facing the heaviest oncoming waves, these structures are exposed to the random and dynamic force of breaking waves as the tide ebbs and floods, a situation only equalled on land in areas of seismic activity. Their height must exceed the maximum tidal range plus an allowance for expected extreme wave heights. As height increases, so must 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 breakwaters failed during construction, while most show evidence of careful rebuilding, frequently after great storms. Sometimes, lack of timely repair resulted in complete loss – as at Trevaunce, where the former harbour is marked only by blocks of dressed stone littering the beach.
While great storms have occurred throughout history, predictions for a worsening wave climate and increasing storminess place maritime infrastructure firmly in the front line of climate change. 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 survived relatively intact. Many man-made 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 breakwaters 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.
|Mullion Cove: the 19th-century harbour is owned by the National Trust which has been exploring options for its long-term sustainable management. A 2006 study concluded that repair and maintenance until ‘failure’ should be adopted, followed by managed retreat – a controlled process of loss and consolidation, after which the harbour would revert to its natural state as a cove. (Photo: John Such, suchgoodpictures.co.uk)|
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, laid 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, while the long open joints allowed seawater to rapidly drain downwards. Quarrying and transport improvements from the mid- 18th century meant that larger units of the densest stone, often massive granite blocks, could be 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 outwards. 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.
|Medieval boulderwork in the Grade II* listed South Quay, Mousehole (Photo: Colin Higgs, www.portreathstudio.com).|
The mid-18th century saw a move towards highly engineered structures. John Smeaton advised on many harbour improvement works but some 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 and the stone reused to build the present North Quay – again, a rubble-filled masonry structure – and the entrance was improved by rebuilding the end of the South Quay with a slight overlap and an outward kick to shelter vessels in the narrow entrance. Later 19th-century structures became increasingly impermeable, designed to deflect oncoming waves, forcing energy outwards and upwards. Mullion’s West Pier, built only 20 years later, has outer skins of tooled masonry with mortared joints, a concrete ‘bagwork’ hearting of ordinary Portland cement and a full-length projecting moulding intended to deflect waves seawards (a precursor to the modern recurve). The increasing use of concrete towards the end of the century introduced a new phase and scale of marine infrastructure.
Mousehole’s evolution highlights the importance of understanding not only fabric and structure, but also changes in harbour plan form. Perhaps the apogee of Cornish harbour construction is Porthleven, where almost every technique known to the 19th-century engineer was employed to overcome its exposure to prevailing south-westerlies and the impulsive breaking of ocean-generated waves which shoal rapidly inshore. Originally a cove fishery, Porthleven was developed by speculators, ostensibly as a harbour of refuge. In 1810 work began to remove the natural sandbar and lay the foundations for a protective pier. This work was repeatedly washed away, so work began from the seaward end landwards which was successful. This structure is angled so that breakers roll along its seaward face and expend themselves upon the reef and occasionally over the Bickford-Smith Institute (1884). Even so, in locally calm conditions, waves generated by distant storms can diffract around the end of the pier and surge along the east outer harbour wall. The first attempt at harbour construction produced a narrow rectangular basin with a wide entrance. Open to incoming breakers, its internal geometry created turbulent conditions which were worse than before – it was a complete failure.
In the 19th-century engineers were aware that small enclosed harbours were the most difficult to design, having less space in which to dissipate wave energy. As Thomas Stevenson remarks, ‘the breaking of a free wave is a very different thing from the breaking of a wave confined by a barrier of masonry. While the first may be compared to the harmless ignition of a loose heap of gunpowder, the other resembles the dangerous explosion produced by the discharge of a cannon’ (The Design and Construction of Harbours, 1874). Substantial rebuilding at Porthleven in 1855 introduced a new breakwater which formed a locked inner harbour, with a sluice that could be opened on the ebb to scour the navigation channel. A protective outer harbour was also formed, where vessels could shorten or set sail, and a high parapet was added to reduce over-topping into the inner harbour.
However, the most significant challenge in this confined site would have been the introduction of sufficient calming measures to dissipate wave energy within the outer harbour. The seaward face of the new breakwater was sloped at a shallow angle and finished in rough-dressed, vertical stonework to absorb rather than reflect wave energy. Its angular re-entrant corners were curved and chamfered to reduce breaking caused by colliding waves, and the existing outer west wall was modified to accommodate a shallow stone apron. This is open to the harbour road and acts as a ‘spending beach’ where waves can break harmlessly. This magnificent structure survives relatively unaltered, now occupied only by a handful of small boats. While the statutory duty to maintain Porthleven as a harbour of refuge still stands, it has been privately owned since 1978 by a company whose core activities do not include harbour management.
The UK is unique in Europe in requiring its port sector to be self-financing. Harbours can be owned by local authorities, private individuals and companies, by associations and by harbour trusts – statutory nonprofit making bodies formed of independent harbour commissioners. As the Crown Estate claims ownership of the seabed from low water to the 12-mile territorial limit and owns approximately half the foreshore of the UK, almost all harbour authorities must lease Crown property within their jurisdiction at a market rent paid to the Treasury. All UK statutory harbours are subject to the same complex regulatory burden, including compliance with the Port Marine Safety Code which imposes a duty to maintain an open port and conserve it for use as a safe harbour. Even where a harbour is closed, proportionate compliance with the code is recommended to ensure health and safety of potential users.
In 1873, Mousehole Harbour Commission purchased the Duchy of Cornwall ‘land’ falling within its authority for the sum of £5. This means the trust is fully independent and able to control its own costs. The harbour is run by volunteers and key staff who are paid a small honorarium. The trust provides support for fishing boats, subsidises moorings for local boats and puts sand into the harbour each year to maintain a sheltered beach for visitors. In 2013, car parking on and around the historic quays accounted for 92 per cent of the trust’s annual income. A small surplus is retained each year enabling the trust to plan for future expenditure, barring the catastrophic loss of the quays, which are not insured.
Mousehole is one of the best preserved harbour settings in Cornwall. Yet the importance of the harbour commissioners in sustainably managing this heritage site is largely overlooked. Cornwall Council is the statutory harbour authority for ten harbours. While some have always been local-authority owned, the council has acted as a safety net for failed trust ports such as St Ives and Porthscatho and failed commercial ports such as Portreath. All remain statutory ports and all are loss-making. As most historic harbour structures are uninsured, many are being maintained to defer eventual failure: few harbour authorities have the resources to plan for future adaptation.
The government’s Small Ports Recovery Scheme, announced in August 2014 with funding totalling £1.7 million, was an unexpected lifeline enabling many harbours, including Porthleven and Mousehole, to make repairs that were otherwise beyond their modest means but critical to their ongoing code compliance. Where a harbour is closed and no open port duty exists, damage from natural causes may go unrepaired. For example, the Grade II 19th-century granite pier at Lamorna Cove is privately owned. Breached in 2014, it was not repaired and wave action has since reduced it to a stub.
|Ruined stub of the privately owned 19th-century granite pier at Lamorna Cove.|
Harbours are subject to sweeping natural change and human alteration, characterised by pragmatic rebuilding and structural discontinuity. Minor repairs are often ad hoc, while major repairs rely on the ingenuity of the consulting engineer. Often, repairs are carried out in a single stage and specified to anticipate worsening conditions, rather than incremental minimum intervention. While fallen stonework may be recovered, the use of modern materials and techniques is common.
Historic inter-tidal structures were not designed to withstand the additional stresses presented by increasing sea levels and storm intensity. Progressive sea level rise in the 20th century means that the effective height of many sea-facing structures has already been reduced, causing amplified wave run-up and an increasing risk of over-topping. At Mevagissey and Looe, for example, over-topping of the quay walls is frequent. But historic masonry structures cannot be raised without risking instability and settlement. Adaptation can involve profound alteration.
Flood resilience may be achieved by pressure grouting, or building an impermeable piled ‘cut-off’ wall against the historic walls and installing lock gates to complete the enclosure. This approach was used at Padstow where the Grade II inner harbour walls are now lined by an impermeable secondary structure on their seaward face. At Looe, an outer harbour, tidal floodgate and cut-off wall have been proposed by Looe Harbour Commissioners. This scheme should also provide all-tide access for the fishing fleet and some townscape improvements.
The survival of harbours with no adjacent community is less certain. Sustainable coastal engineering favours low impact ‘soft’ defences which work with natural change, including ‘managed retreat’. Hard sea defences are now known to contribute to coastal erosion and a review of the shoreline management plan for Cornwall (www. ciscag.org) indicates that resources are likely to be focussed on protecting coastal settlements rather than isolated coastal infrastructure.
The marine environment presents a huge challenge for conservators, engineers and coastal managers and raises uncomfortable questions about the application of accepted conservation principles at the coast which are founded on the concept of reinforcing and ‘handing on’ heritage value. In attempting to articulate the significance of harbour settings, we need to be able to understand the historic fabric, context and setting and to make meaningful comparisons between sites. There is an urgent need for best-practice guidance on maintenance, adaptation and mitigation where partial or complete loss is anticipated and a need to engage more fully with harbour authorities, many of which are conservation bodies in their own right.
A strong multi-disciplinary approach is vital in establishing strategies specific to the specialised marine environment. In the meantime, change at the coast continues apace. This article began with an examination of the historic evolution of harbour infrastructure: without its shelter and protection many coastal settlements were untenable. For many, this remains the case.
This article originally appeared in IHBC's 2017 Yearbook. It was written by Hilary Wyatt, an EPSRC-funded PhD candidate at the Welsh School of Architecture, where she is researching the sustainable conservation of marine infrastructure. Her professional practice includes conservation and design and building surveying. In 2016 she won the Gus Astley Award for her MSc dissertation on small-scale historic harbours.
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