1985 Scenic Bridges

Single 35c 'Shotover bridge' gummed stamp.

The road bridge across the Shotover River in Central Otago was described at its opening in 1975 as "mathematical precision combined with beautiful form". Both these elements, engineering skill and aesthetics, played their part in the design of the bridge which is on a route serving the important tourist area of Queenstown and the Southern Lakes.

The two-lane carriageway is 320 metres long and is made up of 169 pre-cast, pre-tensioned concrete box girder sections, that were made in Dunedin and then transported to the bridge site by rail and road. Each section was lifted into place by a 50 tonne crane and had to meet its mate. Work was made doubly dificult by the extreme Central Otago weather when freezing temperatures in winter and searing heat in summer combined to affect the materials in the bridge.

Single 40c 'Alexandra Bridge' gummed stamp.

Steel was the chosen material for the bridge built over the Clutha River at Alexandra in 1958 to replace a bridge built in 1882. Bridging the river at Alexandra was never an easy proposition. The Clutha is the longest river in the South Island and is reputed to carry the greatest volume of water.

Spanning some 158 metres the new tied-steel arch bridge incorporated special design features. It is anchored to one abutment by means of a hinge and there are bearings, or rollers on the other abutment and all the piers, that allow the bridge to freely expand and contract. The reinforced concrete deckslab is also designed with expansion joints so the deck can 'breathe' with temperature changes.

Single 45c 'South Rangitikei Rail Bridge' gummed stamp.

The South Rangitikei rail bridge forms part of the main trunk railway line north of Mangaweka in the central North Island. It is rugged landscape, scarred with deep gorges that presented many challenges for bridge builders. Flash floods that sometimes sweep down without warning from the high country had to be taken into account in the bride design as did earthquakes which are a constant threat in the area. The South Rangitikei bridge is able to move - in the event of an earthquake the legs of the high slender piers are designed to alternately lift off their foundation base..

Construction began in April 1973. The piers were constucted first and the first span completed. Then in May 1975 the temporary works supporting the partially built second span collapsed, sending several hundred tonnes of material into the river below. Work restarted in September 1975 and quick progress had the bridge completed by August 1981. The spectacular and elegant concrete structure subsequently won an environmental design award.

Single 70c 'Twin Bridges' gummed stamp.

An unusual bridge located at the confluence of the Mangakahia and Awarua rivers in Whangarei county, Northland, is the subject of the fourth stamp. Twin Bridges takes its name from two bridges built there in the 1920s. These were replaced in 1970 by a single reinforced concrete structure but the name remains.

The bridges special feature is a 19m landing which branches off the main bridge, giving access to farm land which would otherwise be isolated by the convolutions of the two rivers. The sealed road leading to Twin Bridges winds through rolling, fertile, volcanic farm land, steep hill country and superb river settings. At the bridge itself, the water is clear and bubbles through rounded river boulders. Native trees on the river bank make it a pleasant and popular picnic spot.