The heritage of the lock islands

The lock islands on the River Severn, with their weirs and associated buildings, are some of the most substantial structures to have been constructed on the canal network.

An aerial view of Diglis Island in 1931 with the Shell-Mex oil depot (Photo: Historic England).

The River Severn is 220 miles long, rising in the mountains of mid Wales and an arterial route for waterborne transport in the west of Britain for more than 2,000 years. It served the Roman settlements at Gloucester and Worcester and Saxon at Tewkesbury, Bridgenorth and Shrewsbury. In the early 1700s the Severn enabled the growth of Coalbrookdale, cradle of the industrial revolution, and later transported Shropshire coal to fuel the salt works in Droitwich and manufacturers in the west midlands. By the middle of the century, flat-bottomed barges, the Severn trows, were carrying cargoes from as far away as Pool Quay in Wales, 128 miles upriver from Gloucester. When pioneering engineer James Brindley created the first canals in the 1760s, the River Severn formed the south-west arm of his vision for a Grand Cross of waterways connecting the heart of industrial England with the ports of Bristol, Liverpool, Hull and London.

The reality of carrying cargo on the river was full of complications. The Severn was affected by both droughts in summer and severe flooding in winter. There are accounts of bargees stuck in the inn at Pool Quay for weeks in dry periods, waiting for enough depth of water over the shoals to move their laden vessels. The tidal range on the lower section of river, second highest in the world, reached 70 miles inland to the bridge at Worcester. Navigating between there and the Bristol Channel was notoriously difficult.

Junctions on the river with the Droitwich Canal in 1771, and the Staffordshire and Worcestershire a year later, led to a great increase in traffic on the Severn. Difficulties grew with the opening of the Worcester and Birmingham Canal in 1815, providing a more direct route from the lower Severn to Birmingham. Despite this, early proposals to improve navigation were defeated by vested interests, particularly those with fisheries on the river and opponents to the introduction of tolls.

Although the construction of the deep Gloucester and Berkeley Canal in 1827 did remove one major obstacle, the treacherous 26 miles of river below Gloucester, it also led to yet more growth of traffic upriver. A survey in 1840 recorded 4,366 cargo vessels plying between Gloucester and Worcester, while records from just earlier indicated 285 days in a three-year period when depth over the shoals was less than 3 feet. Only the smallest of laden craft could pass across this. Eventually, in 1842, after several attempts and much contention, the Severn Navigation Act was submitted and successfully passed.

The scale of the proposals authorised by the Severn Commissioners for improving the Severn under engineers William Cubitt and Edward Leader Williams was unprecedented in Britain. They included the construction of four weirs set diagonally across the river to raise levels between Worcester and the junction with the Staffs and Worcester Canal upriver at Stourport. At each weir an accompanying by-pass channel was excavated and a wide lock with two pairs of timber gates installed to facilitate boat traffic, the ground in between them becoming a new island in the river. The aim was to create a minimum depth of 6 feet (1.8 metres) of water along the entire length of improved navigation.

By 1844 construction of the four weirs and locks, at Diglis, Bevere, Holt and Lincomb, had been completed. The work included new cottages for all the resident lock keepers. Below Worcester the problematic shoals were to be dredged on a regular basis to maintain sufficient depth. This proved only partially successful, so a fifth weir and lock island were created at Upper Lode on the edge of Tewkesbury in 1858, followed in 1871 by two more at Maisemore and Llanthony, where the Severn divides into two channels above and below Gloucester. The scale of these substantial structures was unequalled on the inland canal network. It facilitated an increase in the barge traffic of bulk goods for the west midlands. When that declined, it was followed in the 20th century by the transport of oil and fuel from South Wales to new storage facilities at Stourport and Worcester.

Responsibilities for the new Severn Commissioners covered 42 miles of river navigation between Gloucester and the entrance to Stourport Basin. The river above Stourport remained unimproved but also a free waterway. Below Stourport, boats passing through the locks were now charged a toll, depending on the weight and type of cargo. When the river was in flood, levels could easily rise 10 feet (3 metres) or more and submerge the weir crests. There are several accounts of ‘Wych’ barges laden with salt coming down from Droitwich and shooting over the weirs to avoid having to pay tolls through the locks. Certainly not something for the faint-hearted to attempt.

The centre of operations for the navigation was Diglis lock island, close to the core of Worcester, which had a wharf and maintenance work shop as well as a terrace of three cottages, providing additional accommodation for the company staff. Next to the workshop was a small chapel or ‘Bethel’ for the spiritual benefit of the navvies who worked on the island. Uniquely, Diglis island had a pair of locks side by side, one larger for the wide barges heading to the transhipment basin on the Worcester and Birmingham Canal a short distance upriver. Nearly all these assets, with later additions, are still in use today, although the Bethel was incorporated into an office building and only the stained-glass diamond panels in the iron window frames serve as a reminder of its former function.

A principal task in the workshops at Diglis was the construction of replacement oak gates for the eight locks on the navigation, each weighing several tons. The average lifetime of a pair of gates is approximately 25 years, so this consumed a considerable volume of timber, all of it brought in by barge and unloaded on the wharf. As the only alternative access on to the lock islands has always been via the narrow walkways over the lock gates, boat transport was required for any item not easily carried. The addition of a blacksmith’s workshop allowed all the ironwork for the gate fittings, paddle gearing and lockside furniture to be prepared on site as well. An essential requirement for moving cargo was the wharfside crane. The current example is an electrically driven 15-ton derrick crane built by Butter Brothers and brought up from Cardiff Docks in the 1950s by boat. It is a very visible landmark highlighting the industrial character of the island.

Diglis is an unusual working environment, not least because the Severn has always experienced tremendous floods. Water levels often rise over the locks and flood through the buildings, bringing a carpet of mud and debris. This has happened three times since 2000, and a board by the lockkeeper’s cabin showing high water levels dating back to the 19th century proves it was a problem in the early days too. It can take a week or more for levels to subside and the workshops were fitted so that items could be hoisted above the floodwater for the duration.

Surprisingly the Severn Navigation Commissioners installed little by way of distinguishing branding on their buildings and infrastructure. This contrasted with the canal companies, whose assets, the bridges, locks, cottages and engineering, could be identified by distinctive patterns of design. In the same decade that the Gloucester and Berkeley Canal was adding a characteristic series of classically inspired bridgekeeper’s cottages, those for the lockkeepers on the Severn Navigation were distinguished only by their differences in style. The Diglis workshops adopted a design found in many 19th century canal maintenance buildings across the country, with single-storey, red-and-blue brick walling and a slate roof supported by timber kingpost trusses. The iron latticework windows with brick arches in the principal buildings do give them some distinction as well.

Remarkably few of the historic assets on the lock islands have individual statutory protection. On Diglis the workshops and terrace of cottages are both listed Grade II; at Holt Island the lockkeeper’s cottage is also Grade II. The pair of locks and derrick crane are on the Worcester City local list, and both Diglis and Bevere Islands lie within conservation areas, but for the remaining sites and their assets there are no additional planning controls. It is fortunate that nearly all the original buildings at the lock islands have survived; only the cottage at Bevere has been replaced with a modern dwelling. Responsibility for the Severn Navigation and ownership of the lock islands now rests with the Canal and River Trust. Although most of the cottages have been sold off, those without designation do have restrictive covenants imposed to deter unsympathetic alterations in the future.

While the locks are still in full usage, generally serving leisure boats rather than commercial craft, the Diglis workshops have been through some difficult times. Lock-gate manufacture on the island ceased in the 1990s and the buildings subsequently became little more than storage depots, with increasing deterioration. Finding an alternative use was particularly challenging faced with the significant problems of limited access and risk of flooding. Fortunately things have improved, first with a new tenant for the blacksmith’s shop in 2016 and more recently with the implementation of a major environmental project, Unlocking the Severn.

One result of the construction of the weirs in the 1840s was the interruption of migratory journeys upriver for spawning fish such as salmon, eels and, especially, the twaite shad. In earlier times the shad had been abundant on the Severn but it is now one of the UK’s rarest fish. Awareness that the ecology of our rivers, lakes and coastal waters has been seriously damaged by human interventions led to the development of the EU Water Framework Directive in 2000. One aim was to improve river basins to Good Ecological Status. Unlocking the Severn plans to do this by restoring 158 miles of river habitat while also engaging with local communities. The project, grant aided by the Heritage Lottery Fund and EU LIFE Programme, is a partnership led by the Canal and River Trust, with Severn Rivers Trust, the Environment Agency and Natural England. It will create fish passage for shad and other species across six barriers on the Severn and Teme, and is due to conclude in 2022.

The very significant works have involved cutting through the historic weirs at Diglis, Holt and Lincomb, and the creation of a bypass channel at Bevere, with potential for impacts on buried archaeology. All of this required considerable preparation to minimise damage to the heritage value of the sites and where necessary undertake appropriate mitigation. The project also provided an opportunity to restore and convert the Diglis workshop. It is now a hub for Unlocking the Severn and a museum space suitable for educational and public visits. The workshop retains its heavy machinery and work benches, including the giant mortiser used to make the lock gate joints, and has a display of the hand tools used there in the 19th and 20th centuries.

Two things have helped to preserve the heritage value of the lock islands. One is that after nearly 180 years the navigation continues to function largely in the same way as when it was constructed. The other factor is the commitment by the Canal and River Trust, and before it British Waterways, to protect their historic estate.

This article originally appeared in Context 170, published by the Institute of Historic Building Conservation (IHBC) in December 2021. It was written by David Viner, who worked as a heritage adviser for British Waterways and the Canal and River Trust until his retirement in 2020. He led on heritage support for the Unlocking the Severn project.

--Institute of Historic Building Conservation