Canning Dam
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The Canning Dam and reservoir are a major source of fresh water for the city of
Perth Perth () is the list of Australian capital cities, capital city of Western Australia. It is the list of cities in Australia by population, fourth-most-populous city in Australia, with a population of over 2.3 million within Greater Perth . The ...
, Western Australia. The dam is situated on the Darling Scarp and is an impoundment of the
Canning River The Canning River ( or ) is a major tributary of the Swan River in the South West Land Division of Western Australia. It is home to much wildlife including dolphins, pelicans, swans and many other bird species. Source and route With headwate ...
. It is noted for its innovative structural and hydraulic design that was considered to be at the forefront of concrete
gravity dam A gravity dam is a dam constructed from concrete or stone masonry and designed to hold back water by using only the weight of the material and its resistance against the foundation. Gravity dams are designed so that each section of the dam is ...
design at the time of construction in from 1933 to its completion 1940. The Canning Dam was Perth's primary water supply up until the 1961 when other sources of fresh water were tapped, such as the Serpentine dam. Currently the dam supplies approximately 20 percent of Perth's fresh water. Inflow into the Canning Reservoir is estimated to be , and it has a storage capacity of . Since its completion in 1940, the Canning Dam has contributed to a wide range of environmental and ecological problems in surrounding regions, problems include more common
algal blooms Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...
,
habitat loss Habitat destruction (also termed habitat loss or habitat reduction) occurs when a natural habitat is no longer able to support its native species. The organisms once living there have either moved elsewhere, or are dead, leading to a decrease ...
and
sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to th ...
. Despite these issues, Canning Dam and the adjacent parks and forests provide a variety of recreational activities for the public such as
bushwalking A hike is a long, vigorous walking, walk, usually on trails or footpaths in the countryside. Walking for pleasure developed in Europe during the eighteenth century. Long hikes as part of a religious pilgrimage have existed for a much longer tim ...
, historic walks and
picnic A picnic is a meal taken outdoors (Al fresco dining, ''al fresco'') as part of an excursion, especially in scenic surroundings, such as a park, lakeside, or other place affording an interesting view, or else in conjunction with a public event su ...
facilities.


History

Development of the Canning River as a source of water for
Perth Perth () is the list of Australian capital cities, capital city of Western Australia. It is the list of cities in Australia by population, fourth-most-populous city in Australia, with a population of over 2.3 million within Greater Perth . The ...
was first proposed in a report of the first Metropolitan Water Works Board of Perth in 1896. Investigation of the site began in 1897 when engineer Thomas Hodgson surveyed and proposed the dam's current location as a possible site. However, despite the recommendations of further inquiries, and an extreme shortage of water in some years, government funds were not allocated for the construction of a dam until the
Great Depression The Great Depression was a severe global economic downturn from 1929 to 1939. The period was characterized by high rates of unemployment and poverty, drastic reductions in industrial production and international trade, and widespread bank and ...
in the 1930s. In March 1923, Premier James Mitchell announced that the Canning River would be dammed as part of the Hills Water Supply Scheme, along with Churchman Brook Dam and Wungong Dam. The scheme was intended to rectify severe water shortages in metropolitan Perth. In 1924 a small pipehead dam was built downstream from the present Canning Dam. It was intended as only a quick fix to the water supply problem and it soon became apparent that a major reservoir was needed, although it was nine years before work on the current Canning Dam began. The new dam was completed in 1940 at a cost of £A1.1million, equivalent to in . Engineer Russell Dumas designed the dam and directed most of its construction. A further improvement was made in 1951 when a concrete-lined channel was constructed to divert stream flow from the nearby Kangaroo Gully catchment. The Canning Dam and reservoir was Perth's primary source of water until the boom growth of the city in the 1960s and the completion of Serpentine Dam in 1961. In 1975 the reservoir was connected to Perth's Integrated Water Supply System by the Canning Tunnel. Prior to its opening water had flowed through the Canning Contour Channel to Gosnells. The Canning Dam and reservoir still supplies approximately 20 percent of Perth's drinking water requirements and plays an important role in the context of the development of Perth. The Canning reservoir is also used to store water from Kwinana Desalination Plant. Treated water can be pumped from the plant to the reservoir through the Forrestdale Pumping Station.


Hydrology

The Canning Dam Catchment lies within the Darling Scarp which forms part of an Archaean Shield composed largely of
granite Granite ( ) is a coarse-grained (phanerite, phaneritic) intrusive rock, intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly coo ...
with some invaded linear belts of metamorphosed
sedimentary Sedimentary rocks are types of rock formed by the cementation of sediments—i.e. particles made of minerals (geological detritus) or organic matter (biological detritus)—that have been accumulated or deposited at Earth's surface. Sedime ...
and
volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...
rocks. The dam wall is situated in a narrow
gorge A canyon (; archaic British English spelling: ''cañon''), gorge or chasm, is a deep cleft between escarpments or cliffs resulting from weathering and the erosion, erosive activity of a river over geologic time scales. Rivers have a natural tend ...
running east and west, with rock sides sloping upward from the river bed. Behind the dam wall, the south branch of the
Canning River The Canning River ( or ) is a major tributary of the Swan River in the South West Land Division of Western Australia. It is home to much wildlife including dolphins, pelicans, swans and many other bird species. Source and route With headwate ...
joins the main stream, with the impounded water forming a lake which stretches back in three major arms to the east south-east and south. The catchment has an area of . The reservoir is at AHD and the highest point of the catchment, Mount Cooke is at AHD. Climatically, the area receives about of rainfall per annum with most of this falling between May and September. There is a large variability of rainfall across the catchment however, from between . Since 1975 long-term average rainfalls at the dam wall have decreased by 20 percent and streamflow into the catchment by approximately 60 percent—the average annual inflow between 1948 and 1974 was which had reduced to between 1975 and 2004.


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 Salinity () is the saltiness or amount of salt (chemistry), salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensio ...
or
bacterial Bacteria (; : bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among the ...
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, as with 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 A trench is a type of digging, excavation or depression in the ground that is generally deeper than it is wide (as opposed to a swale (landform), swale or a bar ditch), and narrow compared with its length (as opposed to a simple hole or trapping ...
was sited near the upstream face of the dam, down stream of 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 time. Near-vertical tubular cut-off drains were provided at 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 for chiefly 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 Formwork is Molding (process), molds into which concrete or similar materials are either precast concrete, precast or cast-in-place concrete, cast-in-place. In the context of concrete construction, the falsework supports the shuttering mold ...
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 a violent storm brought of rain in less than two days. As a result, the river rose rapidly, flooding 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.


Remedial works

Recently the Canning Dam has been subjected to considerable cracking of the upper parts of the dam and upper gallery. Investigations have shown that cracking was due to strong alkali aggregate reactivity (AAR) in the concrete. AAR results in swelling of the concrete, which may cause secondary compressive stresses, localised map cracks, and, ultimately structural cracks. In addition, the concrete
tensile strength Ultimate tensile strength (also called UTS, tensile strength, TS, ultimate strength or F_\text in notation) is the maximum stress that a material can withstand while being stretched or pulled before breaking. In brittle materials, the ultimate ...
and elasticity significantly decreases. Many old concrete dams are known to suffer from AAR, including Fontana Dam in
Tennessee Tennessee (, ), officially the State of Tennessee, is a landlocked U.S. state, state in the Southeastern United States, Southeastern region of the United States. It borders Kentucky to the north, Virginia to the northeast, North Carolina t ...
and Pian Telessio dam in Italy. Extensive remedial works were undertaken between 1999 and 2001 to strengthen the dam wall. This work involved removing the top of the existing dam wall and drilling/blasting through the dam wall plus up to a further into the
bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...
below. The top section of the wall was then rebuilt using reinforced concrete. Finally, permanent, re-stressable ground anchors were installed through the formed and drilled holes from the crest to be stressed and grouted into the foundation rock. At time of completion, these were the largest capacity and longest permanent ground anchors installed in the world. An innovative drilling and blasting technique called penetrating cone fracture (PCF) was used in the remedial works process. PCF was chosen over conventional drilling and/or blasting techniques due to the reduced risk of damage to the existing structure from vibration, as well as lower noxious fume and dust levels.


Environmental issues

Since the construction of the Canning Dam, among other
drinking water Drinking water or potable water is water that is safe for ingestion, either when drunk directly in liquid form or consumed indirectly through food preparation. It is often (but not always) supplied through taps, in which case it is also calle ...
supply dams, water flow into the
Canning River The Canning River ( or ) is a major tributary of the Swan River in the South West Land Division of Western Australia. It is home to much wildlife including dolphins, pelicans, swans and many other bird species. Source and route With headwate ...
has been reduced by up to 96%. A number of freshwater fish species
endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...
to the south-west of Western Australia are found in the Canning River system, however studies of fish and fish habitats in the area have shown that fish numbers are low due to a loss of habitat and a loss of linkage between breeding areas due to low flows, preventing fish migrating upstream and reaching important breeding and nursery grounds. Stagnant water caused by a lack of water flow has provided a suitable habitat for successful breeding of an introduced pest, the mosquitofish. Damming of the Canning caused dramatic flow reductions that significantly altered downstream aquatic
macroinvertebrate Invertebrates are animals that neither develop nor retain a vertebral column (commonly known as a ''spine'' or ''backbone''), which evolved from the notochord. It is a paraphyletic grouping including all animals excluding the chordate subphylum V ...
communities. The lack of water flow has also resulted in a poor flushing effect below the dam wall. An excessive amount of nutrients from fertilizers and animal waste has caused
algal blooms Algae ( , ; : alga ) is an informal term for any organisms of a large and diverse group of photosynthetic organisms that are not plants, and includes species from multiple distinct clades. Such organisms range from unicellular microalgae, suc ...
and
eutrophication Eutrophication is a general term describing a process in which nutrients accumulate in a body of water, resulting in an increased growth of organisms that may deplete the oxygen in the water; ie. the process of too many plants growing on the s ...
. Many river pools, which are an important summer refuge and habitat for aquatic and terrestrial flora and fauna, have been lost due to
sedimentation Sedimentation is the deposition of sediments. It takes place when particles in suspension settle out of the fluid in which they are entrained and come to rest against a barrier. This is due to their motion through the fluid in response to th ...
and modification of the flow regime caused by impoundments in the
Canning River The Canning River ( or ) is a major tributary of the Swan River in the South West Land Division of Western Australia. It is home to much wildlife including dolphins, pelicans, swans and many other bird species. Source and route With headwate ...
. Periodic flooding of the Canning River from the dam is required to disperse seed, stimulate
germination Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, ...
and ensure
seedlings A seedling is a young sporophyte developing out of a plant embryo from a seed. Seedling development starts with germination of the seed. A typical young seedling consists of three main parts: the radicle (embryonic root), the hypocotyl (embry ...
survive, recharge shallow
groundwater Groundwater is the water present beneath Earth's surface in rock and Pore space in soil, soil pore spaces and in the fractures of stratum, rock formations. About 30 percent of all readily available fresh water in the world is groundwater. A unit ...
tables that are important during periods of drought, and to discourage and prevent weed growth. However, during times of low rainfall periodic flooding is reduced.


Recreation

A number of recreation activities occur in and around the dam and catchment area. Canning Dam features a number of picnic areas (with gas
barbecue Barbecue or barbeque (often shortened to BBQ worldwide; barbie or barby in Australia and New Zealand) is a term used with significant regional and national variations to describe various cooking methods that employ live fire and smoke to coo ...
s), look outs and historic walks – many with disabled access.
Bushwalking A hike is a long, vigorous walking, walk, usually on trails or footpaths in the countryside. Walking for pleasure developed in Europe during the eighteenth century. Long hikes as part of a religious pilgrimage have existed for a much longer tim ...
occurs throughout the catchment, particularly along the Bibbulmun Track, which passes through the catchment about 10 km upstream of Canning Dam. Several
mountain bike A mountain bike (MTB) or mountain bicycle is a bicycle designed for off-road cycling (''mountain biking''). Mountain bikes share some similarities with other bicycles, but incorporate features designed to enhance durability and performance in r ...
trails run either through the Canning National Park or adjacent State Forest areas. The Canning Reservoir, Canning River and tributaries are illegally fished for marron, especially during summer. Boating, fishing and swimming are prohibited in the reservoir for health and hygiene reasons. Unauthorised camping (including overnight stays and/or outside of designated areas) and unauthorised trail establishment occur more and more frequently in the Canning catchment.


Engineering heritage

The dam received a Historic Engineering Marker from
Engineers Australia Engineers Australia (EA), known formally as the Institution of Engineers, Australia, is an Australian professional body and Non-profit organization, not-for-profit organisation whose purpose is to advance the science and practice of engineerin ...
as part of its Engineering Heritage Recognition Program.


Gallery


See also

*
List of reservoirs and dams in Australia Dams and reservoirs in Australia is a link page for any dam or reservoir (water), reservoir in Australia. Australian Capital Territory There are three key water storage facilities located in the Australian Capital Territory. The fourth source ...
* Swan River


Notes


References

{{subject bar , auto=y , portal=Western Australia Heritage places in Perth, Western Australia Canning River (Western Australia) Dams completed in 1940 Dams in Western Australia Reservoirs in Western Australia 1940 establishments in Australia Recipients of Engineers Australia engineering heritage markers City of Armadale