Travelling along Denwick lane it’s apparent that work is under way just above Denwick Bridge. This is part of an initiative by Northumberland Rivers Trust to improve fish and eel passage at five sites on the River Aln in conjunction with Northumberland Estates. Next to Denwick Bridge an existing fish pass is being replaced, and a resting pool and a new eel pass are being added. The work is necessary under the Salmon and Freshwater Fisheries Act and the Eel Regulations because the weir forms a barrier to migrating species, the existing passes do not work for all species in all conditions, and they are prone to blockages.
The history behind these weirs and fish passes goes back at least 250 years. Perhaps before 1750, when the 1st Duke of Northumberland started to alter his castle grounds (helped by his head gardener, Thomas Call, and Lancelot ‘Capability’ Brown).
North of the river they removed field boundaries, and carefully positioned clumps of trees, to create a naturalistic parkland in the fashionable style. At first the Duke also wanted an artificial lake. They engaged canal builder, James Brindley to advise. Brindley made his reputation by building canals to transport coal to Manchester for the Duke of Bridgewater.
To create an expanse of water for the Duke, Brindley advised introducing a series of cascades to alter and slow the flow of the river. From the castle this would look much like a lake. From the other side of the river they could create a ride, from which the newly restored castle and the surrounding landscape would be reflected in the river.
It isn’t certain when this work was carried out, but the cascades seem to have been constructed in the late 1750’s. They were damaged in the Great Flood of 1771 then rebuilt in 1772 as the weirs we see today. Any earlier structures would have been destroyed by the great flood. So it’s reasonable to assume that the fish pass that is now being replaced was originally added at the same time as the weir (i.e. about 1772).
The fish pass next to Denwick Bridge lies at the upper end of an ancient stone channel that runs under Denwick Lane, and then along the north bank before rejoining the river further downstream. The channel pre-dates the fish pass, and archaeologists have speculated that it is a repurposed mill leat, which could have medieval origins. The current works only affect the top end of this channel. The image below shows the channel just before it disappears under the road. It was taken from a position roughly where the mill appears on the 1760 map (north of the channel, west of the road).
Denwick New Mill (also known as Wythope Mill or Gothick Mill) was constructed in this area, following the great flood of 1770. An illustration of the gothick style Denwick New Mill can be found <here>. This probably represents the view from Denwick Bridge, as described by Tate:
“The Wythope Mill at this time was rebuilt, on an enlarged scale, in an imitative Gothic style. It was a picturesque object, seen from Denwick Bridge; and its removal in 1839 was regretted by many who had often lingered on the bridge listening to the clack, and enjoying one of the finest views of the castle and of the vale of the Aln”.
The older mill that appears here on the 1760 estate plans is also called “New Mill” and the opposite bank of the river is labelled “New Mill Haugh”. So the “Gothic” new mill replaced an earlier “new” mill in the same location. At one time that earlier mill must also have been regarded as “new”. The implication being that it replaced an even earlier mill. Perhaps one day we will be able to trace the history even further back.
This draws heavily on the Archaeology Report that was submitted with the original planning application (19/01807/FUL | Construction of 5 new fish and eel passes at weirs on the river Aln.). <here>.