Sunday, 27 July 2014

The New Tidal Weir at Glasgow Green

Sketch of structure with sluices up

Glasgow Herald, Thursday December 26th 1901

This structure, which is to be opened by the Lord Provost on Saturday, is a somewhat unique type of cross-river bridge, the only similar one in Britain being across the River Thames at Richmond.

The Lord Provost of Glasgow at that time was Samuel Chisholm.

Somewhere about 20 years ago, after much discussion, it was decided by the then Town
Council that the old weir, which consisted of a rough bank of stones and boulders of various
sizes submerged at high water, and which extended across the river about 100 yards east of
Albert Bridge, having a lock for the passage of boats at it’s north-end, should be removed, in the
expectation that various good results would follow, including less dredging in the harbour, and
unimpeding navigation as far as Carmyle.

Far from improving maters, however, the immediate effect of this step was an enormous
amount of scour in the river bed, causing the river banks for long stretches to cave in, and also
seriously injuring the foundations of several of the river bridges, the old Rutherglen Bridge being
the first to show dangerous symptoms, which ultimately led to its being taken down and replaced
by the present handsome structure, whilst the amount of dredging in the harbour was probably
increased by the deposit of the scoured-out material.

After considering the question for some time, and studying the result of the new weir just them
finished at Richmond on the ‘stoney’ principle, the Corporation decided to erect a similar structure
on the site of the old weir, as a result, Parliamentary powers were obtained in 1892.

The work of construction was not begun until a year or so later, but following very severe
flooding, the coffer-dam, which had been constructed by the first firm of contractors who
undertook the work, was undermined and a great amount of damage done, the final result
being that the Corporation took over the works from them. Sir Benjamin Baker, the well known
engineer, was called in by the Corporation, and, after a careful examination, be recommended
the carrying out of the works by the sinking of a series of caissons extending from bank to bank
by the pneumatic process, which he had employed so successfully at the Forth Rail Bridge.
Fresh designs were prepared under the supervision
of the City Engineer, and a new contract was let, the successful offerers being Messrs
Morrison & Mason Limited, and work was again resumed in the latter end of 1896.

The firm of Morrison & Mason specialised in building waterworks, docks, railway
construction, tenements, villas and public and commercial buildings.

Amongst some of their work in Glasgow between 1875 – 1908:
The General Post Office, George Square
Her Majesty’s Theatre (Citizen’s Theatre), Gorbals Street
Clyde Navigation Building (Clyde Port), Broomielaw
Great Western Road Bridge
Ruchill Hospital , Extension to Rottenrow Hospital
Colliseum Theatre
And possibly most famously – Glasgow City Chambers (1882 – 1890)

Progress Of The Work

Since that date the work has been quietly but steadily carried on under many difficulties,
particularly during the winter seasons, which since the work was resumed have been of a
very wet description, the river being in flood to a greater or less degree for weeks at a time.
The delay has arisen chiefly from the great difficulty which was experienced in sinking the caissons
through the solid masonry foundations of the old lock already mentioned and through the boulders
etc., forming the old weir, which had made their way many feet down into the sandy bed of the
river, and caused great deal of trouble when getting below the cutting edges of the caissons.
The series of sill caissons, which were sunk right across the river, had to be finished one by one,
the work at one being completed and the water-way restored before another was started,
this being absolutely necessary owing to the amount of scouring action which immediately took
place when the water-way was restricted by their presence. As only four men could be employed
in one of these caissons at a time, the rate of speed was necessarily slow, and the daily amount
of sinking accomplished, even in the easiest material, very small. They are sunk to a depth of 45
to 50 feet below high water, so that their foundation is well below the limit of any scour which
could possibly occur in the future.

Operations Below Low Water Mark

Very great amount of accurate work had to be carried out below low water mar by the aid of
pumps or by divers, and as even the most powerful pumps were unable to control the water
except for a short period at low water of each day during the period of spring tides, the
operations were necessarily prolonged. In fact, many of the portions of the work carried out
have no precedent in engineering operations, in that no benefit was obtainable from prior
experience gained in similar work, and many expedients were tried from time to time by the
contractors to solve the various problems, and great credit is due to them for the manner in which
they have finally overcome all difficulties. It is also a matter for congratulation that, in spite of the
somewhat risky nature of the pneumatic process of forming foundations, especially in tidal
rivers, no fatal accident has occurred since the commencement.
The structure is now quite complete and the sluices in working order, the only thing remaining
to be done being the drawing of old piling and the placing of a new skin of heavy slag all over the
river bed, so as to prevent any scouring action in the future.

Division Of The Weir

The type of weir adopted, as already mentioned, is that patented by the late F.G.M. Stoney
and consists of three large sluice gates 80 feet long by 12 feet deep, each closing up one of
the three 80 feet spans into which the weir is divided. These gates weigh about 45 tons, but
20 tons of counter-balance weight is provided at either end, so that only five ton net lift remains.
The lower edges of these gates, when down for the purpose of damming up the water on the
upstream side, is in very close proximity to a massive granite sill by the caissons formerly
mentioned, but is not closed right down on it, a sufficient space being left so that just enough
water gets away underneath to ensure that the ponded up water on the upstream side shall
remain at a constantly uniform level. When there is a large amount of water in the river these
openings will be increased, and when a small amount, diminished. At high water, or shortly
after it, the gates are shut down and while the tide recedes on the down-stream side as it does
ordinarily on the up-stream side, the water remains at the level it held when the gates were shut
down, thus ponding up the water, and forming practically a long lake extending beyond
Dalmarnock Bridge, and as a consequence preventing that unsightly exhibition of
mud and garbage, and in summer the objectionable smell from decaying matter which
are observed at the present.

Navigation Arrangements

On the incoming tide rising and reaching the level of the ponded-up water on the up-stream
side, the water pressure on the gates is naturally equalised, and the gates are then lifted and
navigation allowed to go on unimpeded as through an ordinary bridge. As the gates rise they are
tilted over into a horizontal position, until the face of the sluice gate is at the same level as the
crown of the arch, and the appearance of an ordinary bridge is obtained. Each gate is raised and
lowered by a small hydraulic engine situated in the centre of each span, and the process of lowering
or lifting a gate takes about three minutes. As a final result of the undertaking, the dilapidation of
the river banks will be stopped and it is confidently expected that when they are restored, the
stretch of river lying to the east of the weir will once more become a boating centre, and with a
purified river, which is not very far distant, will once more prove an attraction to the citizens, and,
instead of being an eyesore, become the scene of much healthy and enjoyable recreation, not
very different from what obtains on the Thames at present.

Engineers and Contractors

It should be mentioned that the engineer in chief for the whole works has been Mr. A. B.
McDonald, M.Inst.C.E., the City Engineer, with Mr. John Cowan, Assoc. M.Inst.C.E., as
resident engineer, while Messrs Ransomes & Rapier (Limited) of Ipswich, have erected all the
steel work of the superstructure, as well as the ‘Stoney’ sluices, the foundations, masonry, and
general work being executed by Messrs. Morrison & Mason (Limited), Polmadie.

Completed Bridge, 1901 

The bridge remained until 1941 when flooding to the surrounding area
occurred - scour undermining the abutment foundations. At this time, both the structure and
the tenements on Adelphi Street on the south bank were demolished.

The present bridge was completed in 1949 and carries pipes across the river.

Bird's Eye View showing Glasgow Green on the north bank.

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