Canning Dam

The Canning Reservoir is a reservoir in the south-west of the Australian state of Western Australia. It is an important drinking water reservoir for the city of Perth and is located in the Darling Range in the course of the Canning River. The concrete gravity dam had the time of their construction especially modern design and hydraulic design. Until the 1960s, the Canning Reservoir was the most important source of fresh water for Perth; only put you at more reservoirs. Today, the reservoir supplies about 20 % of fresh water for the city. The feed to the Canning Reservoir is estimated at 22 million m³ / year and the memory capacity to 90.352 million m³.

Since its completion in 1940, the Canning Reservoir has a large number of environmental problems, such as more frequent algal blooms, loss of habitats and sedimentation caused. Nevertheless, the Canning Reservoir with its environment is a popular recreation area.

History

The expansion of the Canning River as a source of fresh water for Perth was first proposed in 1896 by the first Metropolitan Waterworks Board of Perth. The site investigation began in 1897 when the civil engineer Thomas Hodgeson measured the site of the present dam and suggested as a possible location. Despite the demands for further studies and an extreme water shortage in a few years you could muster up to the Great Depression in the 1930s, no money for the construction of the dam.

1924 small weir 6 km below the present Canning Dam was built. It was only intended as a quick fix for the problems in the water supply of Perth and it soon became clear that we needed a larger reservoir. However, it took nine years to go until the start of construction of the present dam. 1940, the reservoir was completed at a cost of 1.1 million AU $. Civil Russell Dumas designed the dam and supervised most of the construction.

1951 was built to divert the flow of water from the catchment area of the nearby Kangaroo Gully as an improvement on a concrete paved channel. The Canning Reservoir was up to the boom phase of growth of Perth in the 1960s and until the construction of reservoirs Serpentine 1961, the most important source of freshwater in the city. In 1975, the reservoir was connected by the Canning Tunnel to the Integrated Water Supply Scheme of Perth. Before its opening, the water had flowed through the Canning Contour Channel after Gosnells.

Today, the Canning reservoir still supplies about 20 % of drinking water from Perth and plays an important role in the development of the city.

The Canning Reservoir also serves as storage for the recently completed Kwinana Desalienation Plant ( RO plant). The desalinated water from the plant can be pumped from the Forrestdale Pumping Station into the lake.

Hydrology

The catchment area of the reservoir is located in the Darling Range, which is part of the shield, which consists mainly of granite with some linear deposits of altered sedimentary rocks and volcanic rocks.

The dam is located in a narrow valley that runs in an east -west direction, with rock crashes down to the river bed. Behind the dam joins the Canning River South in the main river. Thus, the water formed a reservoir which has three main arms to the east, southeast and south.

The catchment area is 804 km ². The reservoir is located at 200 m altitude and the highest point in the catchment area, Mt Cooke, is 582 m high.

The annual rainfall is approx 900 mm; most of the rain falls from May to September. However, the distribution of rainfall in the catchment area varies greatly between 700 mm and 1300 mm per year.

Since 1975, the long-term average rainfall at the dam have decreased by 20% and the flow of water in the catchment area by about 60% - the annual water inflow from 1948 to 1974 was 52 million cubic meters, while from 1975 to 2004 only 22 million m³ amounted to.

Construction

The construction of the reservoir Canning ended a long period of insufficient water supply for Perth. It was at this time both quality defects ( salinity or bacterial load, or both) as well as quantity deficiencies. The project, the largest public construction program of the decade, led to a significant growth of the local economy and created about 500 much-needed jobs.

Many innovative design principles and construction techniques that were new to Australia, have been applied in this project. Proven methods that can anwandte the construction of the nearby Wellington reservoir were improved.

In the Canning Dam had, as with all dams, are taken to avoid leakage between the rock camp and the dam. At the Canning Dam was seen in addition to the removal of the rock stock up on the solid stone without breaks a ditch on the water side of the dam before, which was combined with a rock -filled drainage with open, connected tubes to any leakage between the rock camps and the concrete to meet the dam. The installation of an internal drainage system was considered to be novel. Almost vertical, 200 mm thick drainage pipes were spaced along the dam wall mounted in 1.52 m to dissipate internal leakage through the concrete.

In addition to working methods in the then state of the art also labor-saving machines were used to improve the performance in some cases. Support staff was primarily used for Vorortbauten, road construction, excavation for the foundation of the dam, cutting down the surfaces of the lake basin and later for some concrete work. Workers were trained on the dam construction of the formwork into which the concrete was poured needed. These workers were probably hired to normal daily rates, as was customary in this project. The storage of cement in silos was also first used on an Australian construction site, which compared to the then customary handling of cement bags brought about a considerable saving of time.

In general, the work progressed as planned and there were few setbacks from the perspective of the engineers. A major problem, however, occurred soon after the start of construction in March 1934, a bad storm brought 130 mm of rain in less than two days. As a result, the river rose rapidly and flooded the site of the dam foundation. There had to be installed pumps and three days later the work was continued.

In September 1940, the dam was completed. It was then the longest concrete gravity dam in Australia, and also the second highest after the Burrinjuck Dam in New South Wales. In 1997, the Canning Dam was under 90 large concrete and masonry gravity dams in Australia still the fifth highest and sixth- longest. It is the largest concrete dam in Western Australia after crown length and wall volume.

The construction costs were well below the planned amount and the work was completed on time. The construction period was 7 years.

Repair work

In the upper part and the crown went to the dam to significant cracking. Studies have shown that this can be attributed to alkaline reactions in concrete. These reactions lead to a swelling of the concrete, which can cause an increase in secondary compressive stresses and local plans. Ultimately, this leads to cracks in the structure of the concrete wall. In addition, the tensile strength and the elasticity of the concrete to take significantly. Many old concrete dams suffer from these alkaline reactions, including also the Fontana Dam in Tennessee and the Pian Telessio in Italy.

In the years 1999-2001 extensive repair work to strengthen the dam have been made. The upper 3.8 m of the existing dam were removed and drilling and blasting holes introduced into the dam and up to 70 m into the rock foundation under it. The upper part of the dam was constructed of reinforced concrete again. Finally, permanent, restressable ground anchors were inserted through the holes drilled and blasted into the rock foundation. At the time of completion of this work, these were the longest and strongest permanent ground anchors that have ever been built.

A new drilling and blasting technique called Penetrating Cone Fracture (PCF ) was used in these repairs. PCF was preferred to conventional drilling and blasting techniques because of the reduced risk of damage to the existing structure by vibration and a lower incidence of harmful gases and dust.

Environmental problems

Was a result of the construction of the reservoir Canning, as with similar drinking water reservoirs, the water level lowered in the Canning River by up to 96 %. Some freshwater fish species that are endemic to the waters of the southwest of Western Australia, found in the Canning River, but studies on fish and their habitats in the area showed that the number of fish due to loss of habitat and the loss of connection to the spawning grounds is small due to the low water level. The migration of fish upstream to the spawning grounds is greatly hindered. Standing water, which is formed due to low water level has created a life and spawning area for an introduced species, the mosquitofish ( Gambusia affinis ).

The damming of the Canning River has caused a dramatic lowering of the water level that has changed below the dam stocking with microorganisms significantly. The water shortage has also led to a reduced flushing effect below the dam. A huge amount of nutrients from fertilizers and animal excrement has caused algal blooms and eutrophication.

Many pools in the river, which constitute important refuges for aquatic and terrestrial flora and fauna, went through sedimentation and change the flow of water lost, which were caused by the damming of the Canning River.

The periodic flooding of the Canning River from the dam from being required to distribute seed to stimulate germination, ensure that the seedlings survive to replenish low groundwater levels again - which is especially important in times of drought - and curb the growth of weeds. In times of low rainfall, the floods but is reduced.

Activities

At the reservoir and in the vicinity there are various leisure facilities. One finds a number of picnic areas (with gas grill) as lookouts and trails - many of them with access for wheelchair users. You can walk the entire catchment area, especially Bibbulum along the track that leads about 10 km upstream of the dam by the catchment area. Various mountain bike trails criss-cross the Monadnock Conservation Reserve on the Canning River and adjacent state forest.

In the Canning Reservoir, in the Canning River and its tributaries illegal under Marron crayfish ( Cherax tenuimanus or Cherax Cainii ) is fished, especially in the summer. Boating, fishing and swimming are prohibited for reasons of hygiene in the reservoir. Wild camping (including overnight stays outside of designated areas ) and the tort system of trails are in the catchment area of the dam and more frequently. Also, many people drive cars in the area, fishing and hunting wild boar.

External links and sources

• Website of the Canning reservoirs (English)
• Canning Reservoir - WA. ExplorOz.com
• Map of Canning Reservoir, WA. Bonzle.com
• Steve Parish: Australian Touring Atlas. Steve Parish Publishing Pty.. , Acher Field QLD 2007, ISBN 978-1-74193-232-4, p 78