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photo by: Ken W. Watson, 1996
The 62 foot high Jones Falls dam is one of the greatest engineering achievements on the Rideau. Designed by Colonel John By of the Royal Engineers, this dam and associated locks were built under contract by John Redpath, who used up to 40 stonemasons as well as hundreds of Irish and French Canadian labourers to complete the job.
With its height of over 60 feet (18.3 m), it was to be the highest dam built in North America to that time (1827-1832). It was constructed like other Rideau stone keywork dams. The keywork (dressed stones), were the backing of the dam. This stonework is about 27 feet (8.2 m) thick at the base of the dam, tapering to 12 feet (3.7 m) at the top. The dam is built in the shape of an arch which throws the weight of the water that it is holding back into the bedrock on both sides of the dam. It is built using large, 6 foot (1.8 m) long, 3 feet (0.9 m) wide by 2 feet (0.6 m) thick sandstone blocks, placed on end, with about a 1:10 incline (a 1 foot setback for every 10 feet of elevation). Slighly smaller blocks were used as facing stones.
Behind the stone keywork (under the patch of grass beside the stonework in the photo) a five foot thickness of grouted broken stone was placed (to waterproof the dam). On top of that was a sloping apron made of "rubbish" material - clay, gravel and earth. This sloping front was inclined at a 2.5:1 ratio, in other words, with a 62 foot (18.9 m) high dam, the bottom of the slope would extend out 155 feet (47 m) from the base of the dam. Most of this is today hidden under the waters of Sand Lake.
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