Dredging History

 The deposit of mud in the River Tawe had been known about from the earliest of times, and the need to dredge the channel is something that has developed over the centuries. The mud and silt on the bed of the river was known as the layer, and it was considered beneficial for any port to have a thick layer so that sailing vessels could settle to ground at low water without causing any damage to the hull.

       One of the problems encountered with sailing ships was that, without any cargo on board, they were not very stable. To counteract this problem they would load up with large stones as ballast and, when they arrived at their berths, this would be unloaded and maybe used by another vessel leaving the port without cargo. However, It became the practice of many ships to dump this ballast overboard whilst entering the harbour, although the reason for this is not certain. Maybe it was to reduce the time in port, or perhaps to minimise the draught of the vessel so that it could come in on a low tide. Whatever the reason, it was evident from the 1500s that dropping of this ballast, not only at the harbour entrance but also at the wharves within the river itself, was beginning to have a detrimental effect. Ships were damaging their hull timbers by settling on an accumulation of stone rather than on a thick layer of mud at low tide, and a build-up of dumped ballast at the harbour entrance was restricting the size of vessel able to enter the port.  

       In 1583 a Layer Keeper was appointed to curtail this activity and to fine any master responsible for the offloading of ballast into the channel. The stones were removed from the river bed (the layer) and from the ‘bar’ at the harbour entrance in what was probably the first operation of its kind, ultimately leading to the regular dredging of the vast quantities of mud and silt carried daily downstream and deposited within the harbour area by the River Tawe.

 As ports and harbours such as Swansea developed over the centuries, dredgers of various types were utilised to achieve the greater depths of water needed to accommodate ships of ever-increasing sizes. In the early years vessels known as 'spoon' dredgers would have been used in many locations - each boat being operated by a crew of up to five men manually wielding a large scoop on a long pivoted handle to grab up silt from the bottom of the canal or dock. Another early type of dredger consisted of a barge with a rudimentary bucket system powered by a horse, working on a similar principal to a horse gin.

        By the end of the eighteenth century, these little craft were being overtaken by a variety of steam-driven mechanical innovations such as barges mounted with grab cranes, and dredgers with continuous bucket-ladders such as the ‘David Davies’ or the ‘Abertawe’. It is recorded that the first steam dredger was built as early as 1797 for use in Sunderland harbour, and that steam dredgers were used from 1824 to clear the bed of the River Clyde. In fact, it was in the Clydeside ship-building yards of Glasgow that many of these early steam dredgers were actually designed and built. In May of 1845, the Swansea Harbour Master was provided with the sum of £450.00 to purchase a dredger from Totnes in Devon for the deepening of the River Tawe - particularly above the Pottery – although there is, unfortunately, no record of the type of craft he acquired for this task.

      It is interesting to note that a surviving example of a steam-powered bucket-ladder dredger as bought by the Sharpness New Docks Company in 1925 - the ‘SND No. 4’ - can now be seen as a floating exhibit alongside the National Waterways Museum in Gloucester. Also, on show at the Canal Museum at Ellesmere Port is the restored steam pontoon grab dredger ‘Perseverance’, which was built in 1934 for work on the Grand Union Canal. These days, large modern trailing suction hopper dredgers such as the ‘Bluefin’ ‘Marlin’ and ‘Dolphin’ are used by UK Dredging to maintain the required depths of water at ports like Swansea and Port Talbot although, surprisingly, the history of the trailing suction dredger goes back at least to 1907, when the twin-screw sand pump hopper dredger “Lord Desborough” was constructed for the Thames Conservancy Board by Messrs Ferguson Brothers of Glasgow. At the time, this vessel was the largest dredger to be built on the Clyde – her dimensions being 330 ft. by 54 ft. 6 in. by 23 ft. Fitted with double suction pipes arranged to ship inboard, she was capable of raising 4,500 tons of sand per hour from a depth of 70 ft. below water level.