The Most Environment Friendly Bridge

Linn Cove Viaduct is a 379 meter concrete segmental bridge which snakes around the slopes of Grandfather Mountain in North Carolina. Completed in 1987, at a cost of $10 million, it was the last section of the Blue Ridge Parkway to be finished, and considered to be one of the most challenging bridge construction.

The viaduct was built to minimize the damage that a traditional cut-and-fill road would have caused to Grandfather Mountain. Supported by seven massive pillars, the viaduct almost floats in the air without disturbing the land below. To eliminate damage to the environment, no access roads were built for transporting heavy equipment on the ground. The bridge's segments were precast at an indoor facility and transported to the bridge site, where each section was lowered into place by a custom crane placed on either edge of the existing structure. The only construction that occurred at ground level was the drilling of foundations for the seven permanent piers on which the Viaduct rests. Exposed rock was covered to prevent staining from concrete, epoxy, or grout. The only trees cut were those directly beneath the superstructure.

When engineers began constructing the Blue Ridge Parkway in 1935, they knew that building the Parkway that fit the terrain, particularly the Black Rock area of Grandfather Mountain, would be tricky. The whole area consisted of one large mass of boulders, cracked and loose, so conventional road-building practices would not have worked.

A key factor in this controversy was environmental concern. Engineers were faced with a serious question: How to build a road at an elevation of 4,100 feet without damaging one of the world’s oldest mountains? Studies and engineering schemes were done through the early 1970s in search of a plan for routing the Parkway through that area. Finally, the National Park Service landscape architects and Federal Highway Administration engineers agreed the road should be elevated or bridged, where possible, to eliminate massive cuts and fills.

The Linn Cove Viaduct is only the second bridge in history to be built from the end of a span, called a cantilever, which is anchored only at one end. In this case, the cantilever was the road itself. To protect the fragile terrain, all construction was done from the top down and no machinery was allowed more than 50 feet from the base of the piers.

Segments were trucked from a nearby storage area over the completed portion of the bridge to the end of the cantilever. There a stiff-leg crane lifted the segment, swung it out and lowered it to within six inches of the cantilever end. Epoxy was then applied to the joint face and the segment was moved to the cantilever end where the temporary thread bars were installed and stressed.

The contractors developed a special heating system to heat joints for the work to continue through the winter. The concrete used in making the Viaduct was tinted with an iron oxide pigment developed specifically for this project so that the color of the finished bridge would match the color of the one-billion-year-old boulders and cliffs that surround it.

The bridge was completed in November 1987 at a final cost of $10 million. Since then, bridge has received eleven design awards.


Ghadames - Pearl of the Desert

Ghadames, known as the “pearl of the desert”, is an oasis town in the Nalut District of the Tripolitania region in southwestern Libya. It is one of the oldest pre-Saharan cities and an outstanding example of a traditional settlement. The town has a population of around 10,000, mainly Berbers, who live in tightly clustered traditional mud-brick-and-palm houses, packed together like a honeycomb. The houses have a typical vertical architecture - the ground floor is used to store supplies, then another floor for the family, and at the top, open-air terraces are reserved for the women. Rooftop walkways allow women to move freely, concealed from men’s view. Overhanging structures cover the alleys between houses creating an almost underground network of passageways.

Ghademes is an old town. The first records about Ghadames date from the Roman period, when the settlement was known as Cydamus, a fortified city dating back to the 1st century BC. Today it is a small oasis city situated next to a palm grove. None of the surviving buildings date from the protohistoric Berber period, or the period of Roman domination, yet a remarkable domestic architectural style distinguishes Ghadam├Ęs from other pre-Saharan cities and settlements stretching along the northern edge of the desert from Libya to Mauritania. Roughly circular in layout, the historic city of Ghadam├Ęs comprises a cluster of houses. The reinforced outer walls of the houses on the edge of the city form a fortified wall. This rudimentary urban enclosure is penetrated here and there by doors and bastions.

The houses have a minimum of two main floors. The ground floor, which may be sunken, is accessed by a single door that opens onto a narrow hallway leading to a rectangular-shaped room where provisions are stored. At the back there is a staircase that leads to a much more spacious upper level. The first floor generally includes a raised attic and bedrooms, and sometimes a sitting-room. Sometimes there is a second floor with a similar layout. Ground-level living space encroaches upon the blind enclosed passageways along the walls on the ground floor which open onto the city, forming arcades rather than actual streets. At the level of the terraces only the projecting portion formed by the raised attic rises above the roof, marked off by low enclosure walls.

The terraces of adjacent houses are joined with each other forming an open cityscape. The terrace is the domain of women, and gives them a great deal of freedom. Communicating between terraces they make friends with neighbours and can even move about the 'roof' of the city. The covered arcades at ground level are generally reserved for men.

The old part of the town was declared a UNESCO World Heritage site in 1986.


Alatna River

The Alatna River is one of the six federally designated wild and scenic river partially contained within the boundaries of Gates of the Arctic National Park, Alaska. It is called one of the most beautiful rivers in the United States. The Alatna River stems from the central Brooks Range flowing through the Endicott Mountains, passing Circle Lake, the Arrigetch Peaks and Takahula Lake before entering the Helpmejack Hills. The last section of the river continues to flow in a SSE direction through the Alatna Hills into its confluence with the Koyukuk River near the small village of Allakaket. The first 40 km of the Alatna are shallow and rocky, followed by 24 km of a continued shallow area with more rapids. The river then mellows out near Takahula and Circle Lake becoming deeper and more meandering while the scenery turns from mountain peaks into hilly boreal forest. According to The Alaska River Guide, this river is 296 km long from the headwaters to Allakaket and 220 km from Circle Lake to Allakaket.

The river is very popular for float trips due to its calm flow and wonderful scenery. Float trips usually take from four to fourteen days, depending on put-in spot and pick-up spot, and also weather/river conditions. One common place to put in is Circle Lake, a small lake which is float plane accessible and is located in a beautiful part of the valley. Another place to put in is Takahula Lake, a larger, float-plane accessible lake, further downstream from Circle Lake. Gaedeke Lake is also a possible put in spot, but according to the Alaska River Guide, this upstream section near the headwaters of the river is shallow and rocky making portaging or lining necessary. Most floaters take out at the village of Allakaket.