Canning Dam - Construction

Construction

The construction of Canning Dam ended a long period during which Perth's water supply was generally unsatisfactory in quality (either due to salinity or bacterial pollution or both) and in quantity. The project, the biggest public works program of the decade, stimulated significant growth in the local economy and provided desperately needed work for around five hundred men.

Several innovative design concepts and construction methods which were new to Australia were introduced on the project, while others which were used on the nearby Wellington Dam, were improved upon at the Canning dam site.

At the Canning Dam and indeed all dams, care had to be taken to prevent water seepage between the foundation rock and the structure of the dam. At the Canning in addition to cutting back the foundation to solid unfractured rock, a cut-off trench was sited near the upstream face of the dam, down stream which a rock filled drain containing open jointed pipes was provided to intercept any seepage between the rock face and the concrete of the dam. The inclusion of an internal drainage system was considered innovative at the period. Near vertical tubular 8 in (200 mm) cut-off drains were provided at five-foot (1.52 m) intervals along the dam to relieve internal seepage through the concrete.

While state of the art materials-handling methods were used, in some instances labour-saving machinery worked beside operations intended to maximise the labour content. Sustenance workers were employed chiefly for on-site preparation, road construction, foundation excavation, clearing timber from the reservoir basin, and on some concreting operations. Skilled workers were required on the dam for fixing the formwork where the concrete was poured. These workers were probably employed at normal day labour rates, the main employment method used on the project. Bulk handling of cement was also used for the first time in Australia, this saw a significant saving as opposed to bagged cement which was the standard practice of the day.

Generally construction work proceeded smoothly and from an engineering point of view there were few setbacks. However, one did occur in the early stages of construction. In March 1934 there was a violent storm bringing 130 mm (5.12 in) of rain in less than two days. As a result the river rose rapidly which flooded the dam foundation workings. Pumps had to be installed and work resumed three days later.

The dam was completed in September 1940. When built it was the longest concrete gravity dam in Australia, and also the second highest after the Burrinjuck Dam in New South Wales. As of 1997 of the 90 large concrete and masonry gravity dams in Australia the Canning Dam is still the fifth highest and the sixth longest. It is the largest concrete dam in Western Australia in terms of length of crest and volume of concrete.

The final cost of the dam was significantly less than had been originally budgeted for, and the work was completed on schedule to a date that was calculated seven years previously.