Environmental Engineering Reference
In-Depth Information
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self-explanatory. Perhaps the area where least is known is the cumulative impact on
wildlife, particularly land mammals and birds, both wildfowl and land birds. The effect of
human activities and noise on breeding, calving and migration routes is not well
researched. It is certain, however, that there will be a negative impact on wildlife
populations. The passage of tankers or supply ships in Arctic pack ice, for example,
leaves a jumble of broken ice ('freeboard') which can also disrupt the movements of
native people as they travel over the polar ice.
The trans-Alaska pipeline (TAP) is perhaps the most famous oil pipeline in the Arctic
(Plate 24.5), though there is also a smaller 27 cm diameter pipeline from Norman Wells,
North West Territories, to Zama, Alberta, as well as several oil pipelines in European
Russia and north-west Siberia. TAP runs from the Prudhoe Bay oilfields to the ice-free
port of Valdez for a distance of 1280 km. Over half the distance is underlain by
permafrost, much of which was unforeseen, with the result that despite the original
estimate of $900 million, by completion in 1977 the pipeline had cost seven times as
much. Although delays and cost increases were ascribed to the activities of native peoples
and environmental groups, much was due to failure to recognize the problems of the ice-
rich permafrost.
TAP is a remarkable engineering achievement. The temperature of the oil in the pipe
is 65° C, and for more than half its length it is above ground. The supporting members
have been drilled into the permafrost, and each has an automatic refrigeration system
which maintains the permafrost around the footing. The beam supporting the pipe is wide
enough to allow the pipe to move laterally with temperature changes. For those sections
of the course where the pipeline is buried, special insulation coatings 10 cm thick
surround the pipe, and in particularly sensitive areas refrigeration pipes are installed in
the trench below the pipeline to ensure minimal drainage to the permafrost.
The situation with gas pipelines is different from the conditions of oil pipelines. Most
tundra soils exhibit the process of 'frost heave' whereby water moves to the point of
freezing ('the freezing front') and becomes incorporated into the freezing material. This
process can cause the soil to double in volume, and is additional to the well known
expansion of water on freezing of 9 per cent. Natural soils vary greatly in their
susceptibility to heave, so the effects may induce bending in any buried pipeline. In
permafrost areas the temperature of gas in a buried pipeline must be below 0° C. If it
were not, the pipe would cause thawing and subsidence. However, where the pipe with its
chilled gas passes through patches of unfrozen ground, freezing occurs around the cold
pipe, with the likelihood of heave.
North-west Siberia is underlain by sedimentary rocks which contain numerous
hydrocarbon resources. Oil reserves occur in the central region, with natural gas reserves
in the Arctic landscapes along the coast. Development of the natural gas resources has
