Please contact:
Owen Graham
Area Manager Otago-Southland
Tel 03 477 9871
mob 027 431 6701 Email
Corduroy Track, Dunedin: For preservation
Discovered
in the "Wall St" shopping mall development - a corduroy
track built across this area of muddy Dunedin possibly ca. 1850s
Photo: NZHPT
Progress
On 22 July 2008, the Dunedin City Council (DCC) agreed to undertake preservation
work on the 1850's wooden causeway at its 'Wall Street' development site
in central Dunedin.
That work will involve preserving the causeway in situ and displaying
it under a glass floor. The site is located conveniently within an area
already identified for use as a seating and resting area within the new
mall complex.
The initial cost of in situ preservation and display, estimated at $310,000,
will be funded by Dunedin City Council and external fundraising.
Further costs of preservation/conservation of the wooden feature will
need to be met from external sources. The New Zealand Historic Places
Trust has pledged its full support and assistance to identify and access
funding opportunities.
The DCC advises that the proposed work to ensure in situ for preservation
and display will involve:
Driving sheet piling around the edge of the causeway and into the
clay base (4-6 meters below), in order to achieve:
Coffer dam around the causeway.
Reduce potential ingress of storm-water to a level where sump
pumps can prevent flooding during high rainfall and peak underground
water flow events.
Create a structural element into which the mall floor can be connected,
and from which the glass floor can be supported
Connect 180mm I Beams across the top of the sheet piling to:
Provide cross bracing to top of sheet piling
Provide a support for glass floor
Provide a way to run cabling and lighting, and water supply and
mist sprinklers to keep causeway wet.
Fire protection.
Ventilate the sub floor causeway display space:
Provide inlet air entering at east end of sub floor display area
(sourced from the top of the building and run down the inside of the
great wall column).
Provide extract air ducting from the west end of sub floor display
space thus creating air cement through the sub floor display space.
Extract air can be ducted back up the column and expelled at the roof
level.
Provide on the inlet duct facility to fit in future, a heating and
cooling radiator to allow for temperature control.
Fit filters to all ducts to prevent ingress of insects, seeds, pollen
etc.
Provide system to keep the causeway wet by:
Installing water supply pipes and mist sprinklers within the sub
floor display space
Provide a reservoir and dosing system to enable the introduction
of chemical into the water spray or the replacement of water spray
by preservation chemicals (poly-ethylene-glycol).
Provide within the sub floor display space a dewatering sump and sump
pump to
Remove an excess storm-water seeping in from underground creek.
Remove excess water from water spray system.
Remove any excess chemical sprayed or introduced into the sub floor
display area.
Sump will probably have to discharge into the foul sewer.
Provide for display lighting within the sub floor display area.
Probably a water proof fluorescent fitting that is resistant to
chemical and wate and won't produce heat.
Have a 70,000 hour bulb / tube life, that is less likely to cause
ultra violet damage to causeway.
Light fitting can be dimmed.
Provide for fire protection sprinklers to sub floor display space.
(if required)
" Provide structural glass floor and frame based on a 1.5m x
1.5m grid (being maximum glass size).
Dunedin City Council and the NZHPT have agreed that a wood conservation
expert should advise the causeway project team on the conservation requirements.
Work to segregate those parts of the causeway identified for display,
from those parts of the causeway still embedded in the surrounding ground
is proposed for Monday 28 July. This will be done by the project archaeologist
Peter Petchey, cutting through the wooden members at the extremity of
the excavation.
The NZ Historic Places Trust will have two conservators on the site on
Thursday 24 July to discuss the project planning and advise on the protection
and management requirements for the causeway while the preservation and
containment work is underway. That work is expected to take around 3 weeks
to complete.
