Archaeological works for Masbrough Weir fish pass

As part of the works to create a fish pass at Masbrough Weir in Rotherham, an archaeological watching brief was carried out. Here, ArcHeritage tells us about some of the things they found out …

Recent works on the River Don were undertaken on Masbrough Weir at Rotherham to install a larinier fish pass. As the weir is an historic structure, the works were monitored by an archaeologist from ArcHeritage, part of the York Archaeological Trust. Working on a structure submerged within the river offers many challenges. The principal contractor, Bailey Construction Ltd, installed a coffer dam to divert the river around the works area, though the extremely wet weather in February meant that it was not possible to completely prevent water incursion.

View southwest across the weir prior to the fish pass works. Photo by ArcHeritage

The date of the weir is uncertain, though it is first documented in 1722 on a plan of the proposed River Don Navigation. The weir fed water to Rotherham Town Mill, a corn mill that stood on the eastern bank of the river. A mill is likely to have been in this location from the medieval period onwards, and it is possible that the original weir was also medieval. The weir may have been rebuilt along with reconstruction of the Town Mill in 1753. The southwest end of the weir abuts Forge Island, which was created by the construction of the Don Navigation canal. The name comes from the iron forge built by Walker and Co., who leased the island from 1754. The forge was powered by water diverted from the Don, and Walkers’ lease included an annual payment towards maintenance of the weir. Water power was still being used to drive a helve hammer at the iron works in 1858, though steam power was also used at that date. It is likely that water power was no longer used by the late 19th century, and the town mill was demolished between 1888 and 1901. The weir may no longer have had a significant function by that date, but was retained and appears to have been modified on at least one occasion in the 20th century.

Ordnance Survey town plan, published 1888, showing the weir with Forge Island to the left and the town mill above right.

Observation during the cutting of a 50cm deep channel for the fish pass through the southwest end of the weir revealed a core of earth and stone rubble, including some sandstone blocks that may have derived from an earlier structure. This was stabilised by a timber frame of three horizontal cross-beams held in place by upright stakes driven through the core into the riverbed. The upper face of the horizontal beams had been cut to give a sloping profile and they were joined by lap beams reinforced with an iron bolt drilled through the joint. The uprights had pointed ends reinforced with iron ‘shoes’, and were connected to the cross-beams with mortise and tenon joints. An upper surface of sandstone blocks was laid over the core and frame, placed tightly together with no evidence for any type of bonding. The blocks varied from 30cm to 1m in length and were mostly around 25cm wide and 30cm thick. No dating evidence was recovered from the weir, and the timber working methods could have been used at any point from the post-medieval period to the 19th century.

Schematic cross-section through Masbrough Weir. Illustration by Arran Johnson

This was the fifth fish pass installation on the Don to be monitored by ArcHeritage, which has allowed a greater understanding of the typical methods used to construct weirs in the Sheffield and Rotherham area. The earth and rubble core, timber frame and stone surfacing recorded at Masbrough Weir are common to three of the other weirs, though the form and choice of surfacing material may have been influenced by what was cheaply available. For example, at Sanderson’s Weir, Brightside, the surfacing included steel-making waste (crozzle) between larger sandstone ribs, this material being freely available to the steel manufacturers constructing the weir. A fourth weir had a supporting structure of stone rather than timber. Direct dating of these weirs was not possible, but all were extant by the 18th century and at least two had been rebuilt in the early 19th century.

Detail of timber joints used within the weir. Illustration by Arran Johnson