Thursday, 27 Apr 2017
Canning Contour Channel
The Contour Channel is often used by walkers but it is disused and unsafe in places. We have listed it because it can be accessed in some places and is so interesting.
Roleystone has an interesting history regarding our water supply of which the Canning Contour Channel features. Parts of the Contour Channel can be seen in Roleystone and parts have been sold to neighbours of the Channel. It start at the Canning Dam and ends near Martin. The Channel was commenced in 1935 because it was seem to be a cheaper way of transporting water. Previously it was piped from the Canning Dam. It was decommissioned in 1975 when the Canning Tunnel was completed.
The extract below is from the Heritage Council's website. Click here to view more details.
Statement of Significance
The contour channels and associated structures have aesthetic value as the remains of a significant engineering construction that although man-made, sits harmoniously within the natural environment.
The contour channel comprises a series of open concrete channels connected with cast iron pipe siphons over the gullies. The channel follows the contours of the Darling Scarp between Canning Dam and Martin, and is approximately 1.5 metres wide at the base with raking sides at 45o banking up to the natural ground level. At ground level the channel is approximately 5 metres wide, with an overall depth of approximately 2 metres. Together with the channels, there are two stone chimneys and a number of associated works including stilling ponds, a flow measurement building and flume.
The Canning Contour Channel was originally a (16 kilometre long) series of water channels connected by piped sections over gullies, the only contour channel built in Western Australia for the transport of potable water. Built between 1935-37 for the Metropolitan Water Supply, Sewerage and Drainage Board, the Canning Contour Channel had a number of associated works such as the ''stilling'' chambers and the Gosnells Screens (both 1937).
The new contour channel followed the Canning River Valley for a distance of 16kms, to a point in the foothills above Gosnells. From there, a 1.37m pipe took the water to Cannington, where it connected with mains to Fremantle and Mt Eliza. The contour channel walls were constructed of concrete, with a base of local gravel, and were cut into the sides of the hilly terrain. In addition, a number of piped siphons were used to pass the channel water from one side of the valley to the other or to cross under existing roads. As the channel passed through thick bush and, at times, traversed extremely steep-sided valleys and gullies, access was difficult.
Due to the difficult terrain, little mechanization was used in the building of the contour channel. However, light rail tracks were laid in the completed parts of the channel, to take equipment and pipes to the workface. In addition, horses and carts were used to take equipment into the areas that were not too steep. Most of the construction work was, however, carried out by workmen using the basic implements of picks, shovels and wheelbarrows, and simple pulleys, with block and tackle, were used to position the cast iron siphon pipes.
The workers employed on the construction of the channel lived in camps at various places along the channel. The camps utilized tents, with few permanent built structures, except for some stone chimneys, used to dry the workers'' clothing, when required. The ''sustenance'' workers involved in the project were drawn from the large body of unemployed men during this period of economic depression. However, many of the foremen and lead gangers were permanent Water Supply staff. In January 1937, 320 men were laid off when the channel and the pipe main were completed. Water from the Canning Dam was released into twin (parallel) ''stilling chambers'', 200m from the dam, then passed through a flow recorder, and afterwards ran over boarded weirs into the concrete-lined open contour channel to the Gosnells screens. At this point, the water was filtered of any polluting matter, then piped to Perth. From 1954, the water was also chlorinated at the Gosnells site.
The Canning Contour Channel was an integral part of the Perth water supply from the time of its completion until 1975. During the period of its operation, the maintenance of the contour channel was a daily task, for up to three gangs of workmen. Each day during the summer months, an inspector walked the full 16km length to report on its condition. If possible, problems would be dealt with on the spot. Otherwise, the location of the problem would be noted, and a team would then go in to fix any obstructions, or cracks in the concrete walls. Further maintenance work included the removal of algae, clearing vegetation from the banks on either side of the channel, and checking the stability of the land on the high side of the channel to prevent rock falls creating obstructions.
From its commencement of operation, the Canning Contour Channel required constant upkeep to maintain its efficiency. For example, up to 20% of the water flowing along the channel was lost in leakage, with frequent small breaks and cracks requiring regular attention. In addition, when it rained heavily in the catchment area, dirt, bark, leaves and other matter, would pollute the water. In this case, the Gosnells Screens at the terminus of the Canning Contour Channel played an important role in cleaning the water before it entered the main pipeline to Perth.
This filtering system consisted of a battery of six fine wire screens, which removed debris, including the remains of wildlife that became trapped in the swiftly flowing water of the channel. Prior to the installation of the chlorinating plant in 1954, samples of water were taken from the screening chamber weekly, and examined in the bacteriological laboratories of the Health Department.
The Canning Dam was the main source for Perth''s water supply until the completion of Serpentine Dam in 1961. However, despite the vulnerability of Canning Contour Channel to malfunction, it was not until the 1973 that an alternative to this method of transporting water was introduced. At this time, the construction of a tunnel from the Canning Dam to Roleystone was commenced. In 1975, the Canning Contour Channel was decommissioned. On 17 January of that year, the newly completed Canning Tunnel was officially opened, by the Minister for Works and Housing. However, as a precaution, the Canning Contour Channel continued to be maintained in operational order, and opened to a flow of water in the summer for two years after 1975. In 2005, the Canning Contour Channel is no longer used for the transport of water, with the route now used mainly as a walking trail.
SOURCE: State Heritage Office.