Cotswold Canals write:
Bowbridge Lock, Thames & Severn Canal – 18th August 2015
After months of volunteer work, including outstanding work by Waterway Recovery Group volunteers, the lock chamber is ready for gating.
Locally based Ellis Crane Hire expertly carry out the lift of the four gates which were manufactured in EKKI timber by Messrs Hargreaves.
The locks on the Thames and Severn Canal west of Brimscombe are similar to those on the Stroudwater Navigation, and they certainly accommodate the same sized craft.
The first striking difference is the variety of spillweirs at the head of the lock chambers as you proceed up the valley, most of which allowed better maintenance and probably reduced the possibility of blockages in the bywash. The ground paddles are set back from the edge of the lock chamber, reducing possible damage by craft, and the culverts from the ground paddles point directly down the line of the lock chamber, as opposed to being at right angles to the chamber wall on the Stroudwater (which gives the Stroudwater some of the most gently filling locks in the country).
Until the early 1970s there was still an original ground paddle standing at the next lock down ( Wallbridge Upper). The rack on each set of Thames & Severn Canal paddle gear displayed the initials ” T&S Co “, and there were mileage plaques along the route.
Each balance beam on the Thames & Severn joined the heel post by a metal casting which fitted over the heel post, and had two parallel raised lugs to locate it in position.
The Thames & Severn Canal company were presumably trying to construct a more efficient and standardized structure, with far more “batter” on the gates, clearly visible in the tapering in of the heel post towards the centre mitre post at the bottom of the gate.
The lock wall in the chamber could then be built to lean slightly back, increasing the strength of the structure, reducing wear by passing craft and any risk of boats jamming on floating debris or damaged and protuding bricks when rising in the lock. In particular the gates would have a “positive” position of either open or closed, reducing damage to them by craft forcing past a partly opened gate, or sometimes gates sitting party open (or partly shut) and allowing a pound to run out through a more leaky bottom gate. There is nothing more difficult than trying to squeeze a boat past a bottom gate that will not stay fully open.
There would also be far less temptation for boat crews to “slam” and potentially damage the gate by drawing a paddle early to drag a gate closed.
The design was clearly more modern than the Stroudwater Navigation, and diagonal planking on the upper gates reduced damage or the chance of the bow of a boat which is rising in the lock chamber becoming trapped and lifting a top gate, irrespective of it being a 7 foot beam narrowboat or a 16 foot beam Trow.
(By contrast, the Stroudwater Navigation had one or two vertical planks close to the mitre post of the gate where the two gates meet when closed. This only protected the gate from craft of say 16 foot beam.)
All of the new gates being fitted on the Cotswold Canals replicate this attractive safety feature of the Thames & Severn.
The protective circular metal grille over the bypass weir had been designed, fabricated and installed by members of the Stroudwater Canal Society in the early 1970’s and has only recently needed any repairs. The circular weir edge features a small stop plank fitting which would allow the level of the Bowbridge pound to be altered by a few inches. Often attributed to the design of James Brindley on the Stafforshire & Worcestershire canal, circular weirs provide the maximun length of weir edge in the smallest physical area of land. The speed of any floating debris reduces as it approaches the widening weir edge and is thus less likely to accelerate into and block the culvert.
Throughout the day, members of a Waterway Recovery Group summer work camp continue with brickwork repairs between the lock and the road bridge (which will be unblocked in 2016), and clearly show their excitement as they see their hard work coming to fruition.
The redundant gas pipe has been removed from the towpath between lock and bridge, and brickwork repairs to the tail of the lock are well under way. When the bridge work is completed, pedestrians and boat crews will be able to remain safely on the towpath, and not be obliged to cross a busy road.
The road bridge was a superb viewpoint for the day’s activities, with at least three from the very first (1972) working party putting in an appearance.
This restoration forms part of Phase 1a of restoration of the Cotswold Canals and which is generously supported by the Heritage Lottery Fund.