River Derwent (Tasmania)

Etymology

The upper part of the river was named after the River Derwent, Cumbria by British Commodore John Hayes who explored it in 1793. The name is Brythonic Celtic for "valley thick with oaks".

Matthew Flinders placed the name "Derwent River" on all of the river.

The name "River Derwent" was officially endorsed on 20 May 1959.

History

The River Derwent valley was inhabited by the Muwinina people for at least 8,000 years before British settlement. Evidence of their occupation is found in many middens along the banks of the river. The first European to chart the river was Bruni d'Entrecasteaux, who named it the Rivière du Nord in 1793. Later that same year, John Hayes explored the river and named it after the River Derwent, which runs past his birthplace of Bridekirk, Cumberland.

When first explored by Europeans, the lower parts of the valley were clad in thick she-oak forests, remnants of which remain in various parts of the lower foreshore.

There was a thriving whaling industry until the 1840s when the industry rapidly declined due to over-exploitation.

Geography

Formed by the confluence of the Narcissus and Cuvier rivers within Lake St Clair, the Derwent flows generally southeast over a distance of 187 km to New Norfolk and the estuary portion extends a further 52 km out to the Tasman Sea. Flows average in range from 50 to and the mean annual flow is 90 m3/s.

The large estuary forms the Port of the City of Hobart – the deepest sheltered harbour in the Southern Hemisphere. Some past guests of the port include in February 1836, carrying Charles Darwin; the ; and . The largest vessel to ever travel the Derwent is the 113000 t, 61 m high, ocean liner Diamond Princess, which made her first visit in January 2006.

At points in its lower reaches the river is nearly 3 km wide, and as such is the widest river in Tasmania.

The Derwent estuary contains dozens of white sandy beaches, many of which are staples of local activity within Hobart suburbs and include Bellerive Beach, Blackmans Bay Beach, Howrah Beach, Nutgrove Beach, Lords Beach, Long Beach, Taroona Beach, Hinsby Beach, Kingston Beach and Windermere Beach.

Hydro schemes

Until the construction of several hydro-electric dams between 1934 and 1968, the river was prone to flooding. Now there are more than twenty dams and reservoirs used for the generation of hydro-electricity on the Derwent and its tributaries, including the Clyde, Dee, Jordan, Nive, Ouse, Plenty and Styx rivers. Seven lakes have been formed by damming the Derwent and the Nive rivers for hydroelectric purposes and include the Meadowbank, Cluny, Repulse, Catagunya, Wayatinah, Liapootah and King William lakes or lagoons.

River health

The Upper Derwent is affected by agricultural run-off, particularly from land clearing and forestry. The Lower Derwent suffers from high levels of toxic heavy metal contamination in sediments. The Tasmanian Government-backed Derwent Estuary Program has commented that the levels of mercury, lead, zinc and cadmium in the river exceed national guidelines. In 2015 the program recommended against consuming shellfish and cautioned against consuming fish in general. Nutrient levels in the Derwent between 2010 and 2015 increased in the upper estuary (between Bridgewater and New Norfolk) where there had been algal blooms.

Industrial pollution

A large proportion of toxic heavy metal contamination stems from legacy pollution caused by major industries that discharge into the river including the Risdon Zinc Works, a historic smelter establish at Lutana in 1916, and the Boyer Mill at Boyer which opened in 1941.

The Derwent adjoins or flows through the Pittwater–Orielton Lagoon, Interlaken Lakeside Reserve and Goulds Lagoon, all wetlands of significance protected under the Ramsar Convention.

Flora and fauna

The rare spotted handfish (Brachionichthys hirsutus), whose only habitat is in the Derwent estuary and surrounds, The fish is threatened by the Northern Pacific seastar's invasion into southern Australian waters. The Northern Pacific seastar (Asterias amurensis), now firmly established in the Derwent, preys on not only the fish eggs, but also on the sea squirts (ascidians) that help to form the substrate that the fish spawn on.

Bridges

Several bridges connect the western shore (the more heavily populated side of the river) to the eastern shore of Hobart – in the greater Hobart area, these include the five lane Tasman Bridge, near the CBD, just north of the port; the four lane Bowen Bridge; and the four lane Bridgewater Bridge. Until 1964 the Derwent was crossed by the unique Hobart Bridge, a floating concrete structure just upstream from where the Tasman Bridge now stands.

Travelling further north from the Bridgewater crossing, the next crossing point is the Blair Street Bridge at New Norfolk, slightly north of the point where the Derwent reverts from seawater to fresh water, Bushy Park, Upper Meadowbank Lake, Lake Repulse Road, Wayatinah, and the most northerly crossing is at Derwent Bridge, before the river reaches its source of Lake St Clair. At the Derwent Bridge crossing, the flow of the river is generally narrow enough to be stepped across.

Cultural references

The river is the subject of the multimedia performance "Falling Mountain" (2005 Mountain Festival), a reference to the mountain in the Cradle Mountain-Lake St Clair National Park from which the river rises.

The Derwent is mentioned in the song, Mt Wellington Reverie by Australian band, Augie March. Hobart is located in the foothills of Mount Wellington.

Panoramas

References

References

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