Canning Dam Refurbishment
Canning Dam – it’s our largest concrete dam and has been a feature of the Perth hills since 1940, and it still retains all its original Art Deco features – or does it?
Before we answer that question, let’s step back in time – to 1897, when the dam was originally identified as a potential source for water supply. It took over 30 years for the dam’s design to commence in 1930. Several design options were considered but when work began in 1933, a more conventional one was chosen.
This was in part due to the need for sustenance works during the Great Depression, where those who had been unemployed for a long period of time were provided welfare payments or vouchers in exchange for work, which was to have a real social impact on the construction team and community around the dam.
By 1938 over 1,000 men were employed by the Public Works Department (PWD) of Western Australia under the sustenance works scheme designed to give maximum support to the unemployed and their families. Single men received one day’s work per week; married men received two day’s work a week, and those with children received one day’s extra work per child.
It was a very different time back then; and with so many workers in the area, a community and townsite grew during the construction period. Cottages, a post office, shops, and a school were all born around Canning Dam, but no pub (well, at least not officially).
The Resident Engineer’s (RE) home and office survives to this day and were utilised by our own Principal – Asset Protection, Perry Beor during his time as RE back in 2001.
- I was quite delighted to be sitting at the old desk of the dam’s original RE, Victor Munt, Perry said.
- It’s rumoured the desk was originally used by CY O’Connor up at Mundaring – valuing every dollar throughout history.
So back to our question of surviving features at the dam. In 2001, strengthening work was undertaken which involved removing the top 3.8 m (12 feet in old measurements) of the existing dam wall, drilling down through the 70 m high concrete dam, then up to a further 70 m into the bedrock below, and replacing the top section of the wall with a massive reinforced concrete beam.
All this was done reusing the original architectural drawings. Most people don’t realise that the top of the dam had been completely removed but if you look closely at our photos, you can see the line of ‘greyer’ concrete.
Finally, to complete the work, 166 permanent re-stressable (we can tighten or loosen them as required) ground anchors were installed through holes from the top of the dam and secured deep into the foundation rock. The anchors consist of 91 high tensile steel cables measuring about 142 m long (which are still some of the longest ever used in the world). The anchors squeeze the dam onto its foundations and strengthen it considerably – keeping the dam in ‘tiptop’ condition to hold its capacity of 90.5 gigalitres, however it currently sits at around 60% capacity.
Back in 1940 Perth relied heavily on streamflow into our dams, but declining rainfall over time has meant much less streamflow. So, the water in our dams is no longer made up of just streamflow from rain.
Groundwater and desalinated water are stored in these dams so it can be used when it’s most needed.
Author: Perry Beor, Water Corporation, September 2022
