Blair Street Bridge

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Coordinates: 42°46′44.68″S 147°3′24.03″E / 42.7790778°S 147.0566750°E / -42.7790778; 147.0566750
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Blair Street Bridge
Coordinates42°46′44.68″S 147°3′24.03″E / 42.7790778°S 147.0566750°E / -42.7790778; 147.0566750
Carries Lyell Highway
CrossesRiver Derwent
LocaleNew Norfolk
Other name(s)New Norfolk Bridge
Maintained byDepartment of Infrastructure, Energy and Resources
Characteristics
DesignConcrete and steel girder bridge
Total length200 metres (650 ft)[1]
Width12 metres (41 ft)[2]
Height4.6 metres (15 ft)[2]
Longest span35 metres (116 ft)[1]
No. of spans6[3]
Piers in water5[3]
Clearance below4.6 metres (15 ft)[2]
No. of lanes2
History
Construction start1971
Opened1974
ReplacesBridge Street Bridge (c. 1930-1974)
Location
Map

The Blair Street Bridge is a concrete and steel girder bridge carrying the Lyell Highway through the township of New Norfolk across the River Derwent in Tasmania, Australia. Serving as a vital transportation link in the township's infrastructure, the bridge features a single carriageway[3] with separated shared-use pathways on both sides.[4] Completed in 1974, it is the fourth bridge to be constructed at New Norfolk, with the development aimed at withstanding valley floods before the establishment of the Meadowbank weirs.[5][note 1]

History[edit]

Generally known as the "New Norfolk Bridge", similarly placed bridges at New Norfolk have a rich history dating back to the early 19th century. The first wooden bridge constructed across the River Derwent at Bridge Street, near the contemporary Blair Street Bridge was completed in 1834.[7] This bridge was a pivotal development, connecting New Norfolk with the surrounding regions for the first time, facilitating transportation and trade. It was built under the direction of Assistant Surveyor General William Sharland, who owned the 1825 property known as Woodbridge. A toll was collected for crossing the bridge, which was eventually abolished in July, 1880.[8]

Constructed in 1841, the Toll House collected tolls until 1880.

The River Derwent is highly susceptible to flooding[9] and over time, subsequent bridges in 1880[10] and 1931[11] were built near the same location.[12][13] The remnants of the first three bridges, including materials from the original 1834 structure and the later Victorian dressed-sandstone of the second bridge, can still be observed near Woodbridge at the end of Bridge Street.

Before the construction of the Blair Street Bridge, the town of New Norfolk relied on an aging steel and concrete bridge built in 1931 to facilitate transportation across the River Derwent.[14][15][16] However, this bridge had become increasingly inadequate to meet the growing demands of modern traffic, characterised by substandard strength, limited width, and a load limit of 15 tonnes (15 long tons; 17 short tons) imposed in 1966.[17] Recognising the need for a more robust and efficient river crossing, plans were set in motion for the construction of a new bridge.[17]

Construction[edit]

Construction began in August 1971 and finished within two and a half years at a cost of A$900,000.[18] Timber falsework aided river pier access during construction.[19] Foundations use spread footings for abutments and driven piles for piers, ensuring stability and minimising settlement risks. Design emphasises longitudinal and lateral stability for resilience against flooding and adverse weather. Aesthetic features, like minimalist balustrading and lighting, enhance the bridge's modernist appeal.[20] Hydraulic engineers evaluated factors such as river flow rates, water levels, and floodplain characteristics to determine the bridge's susceptibility to inundation during periods of high water.[6]

To minimise the risk of flooding impacting the bridge and its approaches, several design features were incorporated into the Blair Street Bridge project. These included raising the bridge deck to a predetermined elevation above anticipated flood levels, providing sufficient clearance for floodwaters to pass underneath without causing structural damage. Additionally, the bridge's abutments and piers were reinforced to withstand the hydraulic forces exerted by floodwaters.[21]

The completed Blair Street Bridge measures 200 metres (650 ft) with six spans, each 35 metres (116 ft) long over the river.[3] It features reinforced concrete slabs for stability and steel girders fabricated by Russell Allport & Co in Moonah. The bridge design includes a 4.74% graded slope, easing to a 3% vertical curve on Montagu Street,[22] ensuring resilience to heavy loads and adverse weather.[23]

Significance[edit]

Upon its completion, the Blair Street Bridge represented a significant advancement in the town's infrastructure, offering improved safety, efficiency, and convenience for residents and visitors. The Blair Street Bridge eliminated the constraints imposed by the old structure, providing unrestricted access for vehicles and pedestrians while enhancing connectivity between the town's two main centres of development.[citation needed]

Notes[edit]

  1. ^ The River Derwent severely flooded at New Norfolk on Saturday 23 April 1960. It was estimated this flood approximated a once in fifty year flood with a flow of 120,000 cusecs.[6]

References[edit]

  1. ^ a b Department of Public Works Tasmania 1970, p. Appendix No.2.
  2. ^ a b c Department of Public Works Tasmania 1970, p. Appendix No.1.
  3. ^ a b c d Department of Public Works Tasmania 1970, p. 15.
  4. ^ Department of Public Works Tasmania 1970, p. 10.
  5. ^ Department of Public Works Tasmania 1970, p. 3.
  6. ^ a b Department of Public Works Tasmania 1970, p. 12.
  7. ^ "Opening of the New Bridge at New Norfolk", The Mercury, vol. XXXVI, no. 5924, Tasmania, Australia, p. 3, 4 June 1880, retrieved 29 December 2023 – via National Library of Australia
  8. ^ "Memories Of Old New Norfolk Revived By Octogenarian". The Mercury. Vol. CLXIX, no. 24, 398. Tasmania, Australia. 19 February 1949. p. 24. Retrieved 6 March 2024 – via National Library of Australia.
  9. ^ Land and Water Management Branch; Resource Management and Conservation Division (2000). "River Derwent Flood Data Book" (PDF). Tasmanian Government. p. 6. Archived from the original (PDF) on 27 September 2023. Retrieved 7 March 2024.
  10. ^ "Opening Of The New Bridge At New Norfolk". The Mercury. Vol. XXXVI, no. 5924. Tasmania, Australia. 4 June 1880. p. 3. Retrieved 7 March 2024 – via National Library of Australia.
  11. ^ "New Norfolk Bridge". The Mercury. Vol. CXXXV, no. 19, 977. Tasmania, Australia. 18 August 1931. p. 9. Retrieved 7 March 2024 – via National Library of Australia.
  12. ^ Alfred Mault (1 January 1884), The River Derwent: Note upon the flood of 23rd September, 1884, retrieved 6 March 2024
  13. ^ "The River Derwent In Flood At New Norfolk". The Mercury. Vol. CXLV, no. 20, 537. Tasmania, Australia. 25 August 1936. p. 9. Retrieved 6 March 2024 – via National Library of Australia.
  14. ^ "New Norfolk Bridge", The Mercury, vol. CXXII, no. 17, 933, Tasmania, Australia, p. 9, 17 April 1925, retrieved 30 December 2023 – via National Library of Australia
  15. ^ "New Norfolk Bridge: Council Urge Completion, Old Bridge Removal", The Mercury, vol. CXXXV, no. 19, 997, Tasmania, Australia, p. 3, 10 September 1931, retrieved 30 December 2023 – via National Library of Australia
  16. ^ * "New Norfolk Bridge: Piles Strengthened", The Mercury, vol. CXXXVI, no. 20, 117, Tasmania, Australia, p. 6, 29 January 1932, retrieved 30 December 2023 – via National Library of Australia
  17. ^ a b Department of Public Works Tasmania 1970, p. 5.
  18. ^ "Foggy conditions in historic precinct". New Norfolk and Derwent Valley News. 15 June 2018. Archived from the original on 7 March 2024. Retrieved 7 March 2024.
  19. ^ Department of Public Works Tasmania 1970, p. 19.
  20. ^ Department of Public Works Tasmania 1970, p. 18.
  21. ^ Department of Public Works Tasmania 1970, p. 9.
  22. ^ Department of Public Works Tasmania 1970, p. 11.
  23. ^ Wilson, D. R.; Ratcliffe, S.; Krohn, Simon.; Hydro Tasmania, issuing body.; Tasmania. Department of Primary Industry, Fisheries and Energy, issuing body.; Hydro Electric Commission, issuing body.; Tasmania. Rivers and Water Supply Commission, issuing body. (1992), "3 online resources (74 unnumbered pages, 2 maps) : graphs, maps, tables.", New Norfolk flood plain study, Report (Tasmania. Hydro-Electric Commission. Water Resources Department), Hobart, Tasmania: Hydro Electric Commission, Tasmania, nla.obj-2356617050, retrieved 6 March 2024 – via Trove{{citation}}: CS1 maint: multiple names: authors list (link)

Sources[edit]

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