Size Debate

The design of the Rideau Canal – and in particular the proposed width, depth, and length of the locks – was subject to many years of surveys, estimates, debates, and revisions. The canal’s width and depth had serious implications for its military use, as certain ships would not be able to traverse smaller designs. In 1824, more than 40 years after surveying of the canal route began, Samuel Clowes submitted his detailed survey, cost estimate, and three proposed design approaches to the Board of Ordnance. His most modest proposal featured locks only 10 feet (3 metres) wide with a total construction cost of £62,000, while his most ambitious plan involved 20-foot-wide (6 metres) locks and a cost of £230,000. When Lt. Col. By took charge of the project in 1826, he immediately resurveyed the route and suggested that the locks needed to be even bigger – 50 feet (15 metres) wide – in order to accommodate both the military’s new fleet of large naval steamboats and commercial steamboat traffic. In the end, the Board of Ordnance settled on 33-foot-wide (10 metres) locks, which were wide enough for naval, and eventually commercial, steamboats.

Points of Interest

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Source: “Various Lock Proposals” [Animation]. Dr. Stephen Fai. Carleton Immersive Media Studio. 2012.

Duration: 28 seconds
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Various Lock Proposals

The actual size of the Bytown Locks represents a compromise between the Ordnance Department which was funding the project – and Lt. Col. By, who was overseeing the canal’s design and construction. While the Ordnance Department advocated for a 20-foot-wide (6 metres) lock system only big enough to accommodate military gunboats, By pushed for a more versatile design with 50-foot-wide (15 metres) locks, arguing that construction costs could be offset by allowing commercial steamboats access to the waterway. In 1828, the Ordnance Department finally approved the construction of a 33-foot-wide (10 metres) lock system, which was seen as an ideal compromise between immediate investment and future utility.

Drawing of a plan and section of the 20’ lock designEnlarge

Source: Unknown Artist, “Plan and Sections of the Eight Lock, 10 feet Lift. Estimate of Masonry…”, [1842], Library and Archives Canada, NMC-5239

Samuel Clowes’s 20-foot (6-metre) Lock Proposal

This 20-foot-wide (6 metres) lock design, proposed by surveyor Samuel Clowes in 1824, was modelled after Montreal’s recently completed Lachine Canal. The Board of Ordnance initially concluded that they should be able to construct the 202-km waterway according to these dimensions; this decision, however, was eventually overturned as it would have allowed for the passage only of smaller military gunboats, thus limiting the Rideau Canal’s potential versatility.

Drawing of a plan and section of the 50’ lock designEnlarge

 Source: Great Britain Army Corps of Royal Engineers, “Plan and Sections of the Large Lock Proposed by Lieut. Col. John By, Royal Engineers, Commanding Rideau Canal 1st December 1827”, [1827], Library and Archives Canada, NMC-21871

John By’s 50-foot (15-metre) Lock Proposal

This 50-foot (15-metre) lock design was proposed by Lt. Col. John By in 1826. He believed that the Rideau Canal had the potential to generate revenues as a commercial waterway in addition to serving its military purpose. Increasing the lock size to 50 feet by 150 feet (15 metres by 46 metres) would have allowed for the passage of larger steamboats that could transport more men in times of war and provide adequate storage for commercial trade. By argued that civilian steamboat trade would provide the government with an additional income through tolls, helping offset the construction cost of the canal. Although By was unable to convince the Board of Ordnance to build locks of this magnitude, his arguments were crucial to enlarging the proposed 20-foot (6-metre) locks to their current 33-foot (10-metre) dimension.

Drawing of a plan and section of the 33’ lock designEnlarge

Source: Great Britain Army Corps of Royal Engineers, “Plan of the Approved Locks for the Rideau Canal, Lt. Col. By Commanying Royal Engineer John By, Lt. Colonel Roy’l. Engrs. Com’g. Rideau Canal, 8th July 1828”, [1828], Library and Archives Canada, NMC-21893

Approved 33-foot (10-metre) Lock Proposal

The 33-foot (10-metre) locks that were eventually chosen were the result of decades of surveys and years of debate that stretched across continents. While they ultimately didn’t match By’s grandest vision, they did satisfy his desire to accommodate a wider range of vessels and watercraft. The chosen dimensions were especially prescient, since the canal was never actually used for its original military purposes, becoming instead a successful commercial and recreational route. Upon its completion in 1832, the canal’s final cost came to a whopping £822,000 – almost five times the Board of Ordnance’s original estimate.

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