The Trevallyn Dam is a dam on the

South Esk River The South Esk River, the longest river in Tasmania, is a major perennial river located in the northern region of Tasmania, Australia. Location and features The South Esk springs from the eastern foothills of the Ben Lomond plateau near Mathinn ...

in Launceston, Tasmania, Australia and is used to provide water for

hydroelectricity Hydroelectricity, or hydroelectric power, is Electricity generation, electricity generated from hydropower (water power). Hydropower supplies one sixth of the world's electricity, almost 4500 TWh in 2020, which is more than all other Renewabl ...

. The dam was completed in 1955 as part of the Trevallyn Hydro Electric Scheme and now holds the waters of Lake Trevallyn.

Specifications

Lake Trevallyn is a concrete gravity dam built on

Dolerite Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grained ...

bedrock. The spillway height is 26.8 metres and the dam wall is 177 metres long. The lake has a surface area of 1.48 km² and storage capacity of 12.33 million m³. ANCOLD lists Trevallyn Dam as having a dam wall height of 33 metres and the total volume of the wall as 61,000 cubic metres. The dam diverts water to the

Trevallyn Power Station The Trevallyn Power Station is a run-of-the-river hydroelectric power station located in the northern Midlands region of Tasmania, Australia. The power station is situated on the Great Lake and South Esk catchment and is owned and operated by ...

through a 3.2 km tunnel.

Lake Trevallyn

Lake Trevallyn is the long, narrow lake created by the dam and extends as far as

Hadspen Hadspen is a town on the South Esk River in the north of Tasmania, Australia, south west of Launceston. Hadspen has few commercial establishments and is primarily a residential suburb of nearby Launceston. Most of the town's buildings are re ...

where the first rapids begin at the junction of the

Meander A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank ( cut bank) and deposits sediments on an inner, convex bank ...

and

s. The widest point on the lake is at Stephenson's Bay where it reaches 390m wide. Launceston's outer suburb of Blackstone Heights and part of the Trevallyn State Recreation Area form part of the shore of Lake Trevallyn. Land around the lake is a mixture of suburbs, agricultural land and dry

eucalypt Eucalypt is a descriptive name for woody plants with capsule fruiting bodies belonging to seven closely related genera (of the tribe Eucalypteae) found across Australasia: ''Eucalyptus'', '' Corymbia'', '' Angophora'', ''Stockwellia'', ''Allosyn ...

forest.

Facilities

The lake and some of the surrounding land is used as a recreation area. Most facilities are located at Aquatic Point which include a boat launching ramp, jetty and ski-jump. A walking track connects Aquatic Point to the dam wall and Trevallyn State Recreation Area. The dam wall features a viewing platform, parkland and barbecue facilities. Most areas of the lake are open to boating and fishing with the exception of waters near the dam and penstock intake.

Algal Blooms

Lake Trevallyn is often prone to algal blooms in the warm summer months. The blooms are due to high nutrient levels from sewerage treatment and fertilizers, limited water movement and warm temperatures. The main species is

Anabaena circinalis ''Anabaena circinalis'' is a species of Gram-negative, photosynthetic cyanobacteria common to freshwater environments throughout the world. Much of the scientific interest in '' A. circinalis '' owes to its production of several potentially harmf ...

and though it has the potential to be toxic, no blooms recorded in the lake have proven to be toxic to date. Since 2007, a monitoring program has been in place to keep a check on algal levels and to notify authorities when blooms occur.

Jellyfish

In 2009, scientists discovered the freshwater jellyfish,

Craspedacusta sowerbyi ''Craspedacusta sowerbii'' or peach blossom jellyfish is a species of freshwater hydrozoan jellyfish, or hydromedusa cnidarian. Hydromedusan jellyfish differ from scyphozoan jellyfish because they have a muscular, shelf-like structure called a ...

, in the waters of Lake Trevallyn close to Blackstone Heights. Believed to have been brought by migrating birds from

China China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and ...

, the jellyfish were accidentally discovered during routine water testing. The jellyfish are non-venomous and translucent with average sizes around 2 cm across. Though introduced, the jellyfish are believed to have a beneficial impact on the area as they consume the larvae of mosquitoes. A few specimens were temporarily displayed at the

QVMAG The Queen Victoria Museum and Art Gallery (QVMAG) is a museum located in Launceston, Tasmania, Australia. The QVMAG is the largest museum in Australia not located in a capital city. History The foundation stone for the original building to ...

in Launceston after the discovery was made.

References