Cosgrove aqueduct
Encyclopedia
Cosgrove aqueduct is a navigable cast iron
trough aqueduct
that carries the Grand Union Canal
over the River Great Ouse
, on the borders between Buckinghamshire
and Northamptonshire
at the northwest margin of Milton Keynes
in England
. The present structure was built in 1811, to replace a previous brick structure that had failed. When the present structure was erected, it was known as the "Iron Trunk".
The structure has two cast iron trough spans, with a single central masonry pier. The abutments were constructed in masonry but have been refaced in brick during the twentieth century. The trough is 15 feet (4.6 m) wide, 6 in 6 in (1.98 m) deep, with a total length of 101 feet (30.8 m). The canal surface is about 40 feet (12.2 m) above the surface of the river. There are large approach earthworks about 36 feet (11 m) high above the valley floor and 150 feet (45.7 m) wide, with a total length of half a mile (800m).
(later absorbed into the Grand Union Canal
) required to cross the course of the River Great Ouse
, the lowest point between the summits at Tring and Braunston. Initially flights of locks, four at the southeast and five at the northwest, were used to allow the canal to descend to cross the river on the level, and this arrangement came into action in 1800. However William Jessop
, the canal company’s engineer, designed a three-arch brick viaduct so that the canal could cross at a higher level, reducing the water loss and delay in locking down to river level.
His structure was opened on 26 August 1805, but a section of the canal embankment collapsed in January 1806; this was repaired, but the aqueduct structure itself collapsed in February 1808, severing the canal.
Although Jessop is sometimes blamed for the failure of the first structure, the collapse actually led to a legal dispute with the original contractor. The issue went to trial, with damages eventually being awarded to the Grand Junction Company for loss of trade while the canal was out of action, and the cost of the replacement aqueduct.
at Pontcysyllte and elsewhere, had become proven, and Bevan adopted the system for his structure. However, the canal was then operating as a wide canal in contradistinction to some northern narrowboat
canals, so that the troughs had to be substantially larger and stronger than elsewhere.
The cast iron units were cast at the Ketley foundry at Coalbrookdale
; the company had already been involved with Telford on the Longdon-on-Tern
aqueduct. They were transported to Cosgrove by the canal itself, and assembled and erected at site. The new structure was completed in January 1811.
The towpath is cantilevered from one side, as at Pontcysyllte, and supported by diagonal struts.
There is a cattle creep in the embankment either side of the main structure; cattle creeps are small field-to-field access openings for farm animals and occasionally, as in this case, pedestrians.
Cast iron
Cast iron is derived from pig iron, and while it usually refers to gray iron, it also identifies a large group of ferrous alloys which solidify with a eutectic. The color of a fractured surface can be used to identify an alloy. White cast iron is named after its white surface when fractured, due...
trough aqueduct
Aqueduct
An aqueduct is a water supply or navigable channel constructed to convey water. In modern engineering, the term is used for any system of pipes, ditches, canals, tunnels, and other structures used for this purpose....
that carries the Grand Union Canal
Grand Union Canal
The Grand Union Canal in England is part of the British canal system. Its main line connects London and Birmingham, stretching for 137 miles with 166 locks...
over the River Great Ouse
River Great Ouse
The Great Ouse is a river in the east of England. At long, it is the fourth-longest river in the United Kingdom. The river has been important for navigation, and for draining the low-lying region through which it flows. Its course has been modified several times, with the first recorded being in...
, on the borders between Buckinghamshire
Buckinghamshire
Buckinghamshire is a ceremonial and non-metropolitan home county in South East England. The county town is Aylesbury, the largest town in the ceremonial county is Milton Keynes and largest town in the non-metropolitan county is High Wycombe....
and Northamptonshire
Northamptonshire
Northamptonshire is a landlocked county in the English East Midlands, with a population of 629,676 as at the 2001 census. It has boundaries with the ceremonial counties of Warwickshire to the west, Leicestershire and Rutland to the north, Cambridgeshire to the east, Bedfordshire to the south-east,...
at the northwest margin of Milton Keynes
Milton Keynes
Milton Keynes , sometimes abbreviated MK, is a large town in Buckinghamshire, in the south east of England, about north-west of London. It is the administrative centre of the Borough of Milton Keynes...
in England
England
England is a country that is part of the United Kingdom. It shares land borders with Scotland to the north and Wales to the west; the Irish Sea is to the north west, the Celtic Sea to the south west, with the North Sea to the east and the English Channel to the south separating it from continental...
. The present structure was built in 1811, to replace a previous brick structure that had failed. When the present structure was erected, it was known as the "Iron Trunk".
The structure has two cast iron trough spans, with a single central masonry pier. The abutments were constructed in masonry but have been refaced in brick during the twentieth century. The trough is 15 feet (4.6 m) wide, 6 in 6 in (1.98 m) deep, with a total length of 101 feet (30.8 m). The canal surface is about 40 feet (12.2 m) above the surface of the river. There are large approach earthworks about 36 feet (11 m) high above the valley floor and 150 feet (45.7 m) wide, with a total length of half a mile (800m).
Origins
The Grand Junction CanalGrand Junction Canal
The Grand Junction Canal is a canal in England from Braunston in Northamptonshire to the River Thames at Brentford, with a number of branches. The mainline was built between 1793 and 1805, to improve the route from the Midlands to London, by-passing the upper reaches of the River Thames near Oxford...
(later absorbed into the Grand Union Canal
Grand Union Canal
The Grand Union Canal in England is part of the British canal system. Its main line connects London and Birmingham, stretching for 137 miles with 166 locks...
) required to cross the course of the River Great Ouse
River Great Ouse
The Great Ouse is a river in the east of England. At long, it is the fourth-longest river in the United Kingdom. The river has been important for navigation, and for draining the low-lying region through which it flows. Its course has been modified several times, with the first recorded being in...
, the lowest point between the summits at Tring and Braunston. Initially flights of locks, four at the southeast and five at the northwest, were used to allow the canal to descend to cross the river on the level, and this arrangement came into action in 1800. However William Jessop
William Jessop
William Jessop was an English civil engineer, best known for his work on canals, harbours and early railways in the late 18th and early 19th centuries.-Early life:...
, the canal company’s engineer, designed a three-arch brick viaduct so that the canal could cross at a higher level, reducing the water loss and delay in locking down to river level.
His structure was opened on 26 August 1805, but a section of the canal embankment collapsed in January 1806; this was repaired, but the aqueduct structure itself collapsed in February 1808, severing the canal.
Although Jessop is sometimes blamed for the failure of the first structure, the collapse actually led to a legal dispute with the original contractor. The issue went to trial, with damages eventually being awarded to the Grand Junction Company for loss of trade while the canal was out of action, and the cost of the replacement aqueduct.
The second structure
As a temporary measure the lock system originally installed was brought back into use, and Benjamin Bevan, an engineer employed by the canal company, designed a replacement structure. By this time, cast iron trough aqueducts designed by Thomas TelfordThomas Telford
Thomas Telford FRS, FRSE was a Scottish civil engineer, architect and stonemason, and a noted road, bridge and canal builder.-Early career:...
at Pontcysyllte and elsewhere, had become proven, and Bevan adopted the system for his structure. However, the canal was then operating as a wide canal in contradistinction to some northern narrowboat
Narrowboat
A narrowboat or narrow boat is a boat of a distinctive design, made to fit the narrow canals of Great Britain.In the context of British Inland Waterways, "narrow boat" refers to the original working boats built in the 18th, 19th, and 20th centuries for carrying goods on the narrow canals...
canals, so that the troughs had to be substantially larger and stronger than elsewhere.
The cast iron units were cast at the Ketley foundry at Coalbrookdale
Coalbrookdale
Coalbrookdale is a village in the Ironbridge Gorge in Shropshire, England, containing a settlement of great significance in the history of iron ore smelting. This is where iron ore was first smelted by Abraham Darby using easily mined "coking coal". The coal was drawn from drift mines in the sides...
; the company had already been involved with Telford on the Longdon-on-Tern
Longdon-on-Tern
Longdon-on-Tern is a village in east central Shropshire, England. It is in the unitary district of Telford and Wrekin, and is approximately east of Shrewsbury and north-west of Telford....
aqueduct. They were transported to Cosgrove by the canal itself, and assembled and erected at site. The new structure was completed in January 1811.
Structural details
To resist the substantial additional loading of a wide canal, Bevan designed the floor sections to be arched, providing additional strength; in addition there are arch ribs built in with the trough side plates to give additional shear strengthThe towpath is cantilevered from one side, as at Pontcysyllte, and supported by diagonal struts.
There is a cattle creep in the embankment either side of the main structure; cattle creeps are small field-to-field access openings for farm animals and occasionally, as in this case, pedestrians.
See also
- Canals of the United KingdomCanals of the United KingdomThe canals of the United Kingdom are a major part of the network of inland waterways in the United Kingdom. They have a colourful history, from use for irrigation and transport, through becoming the focus of the Industrial Revolution, to today's role for recreational boating...
- History of the British canal systemHistory of the British canal systemThe British canal system of water transport played a vital role in the United Kingdom's Industrial Revolution at a time when roads were only just emerging from the medieval mud and long trains of pack horses were the only means of "mass" transit by road of raw materials and finished products The...