Environmental Engineering Reference
In-Depth Information
drill rig to bore a hole for a stable foundation for a transmission tower. If water is encountered,
pumps will be used to move the water to either adjacent upland areas or to waiting tanker trucks
for proper disposal. When bedrock is close to the surface or when subsoils primarily consist of
large boulders and cobbles, blasting may be required. Heavy trucks carry concrete to boreholes
to construct foundations for transmission structures. Cranes then erect towers on the foundations.
Finally a transmission wire is strung between towers using large pulleys. After construction is
completed, the right-of-way is graded, and agricultural soils are decompacted. New transmission
lines are built with a grounded shield wire placed along the top of the poles, above the conduc-
tors. Typically, the shield wire is bonded to ground at each transmission structure. This protects
the transmission line from lightning. Transmission poles, like trees or other tall objects, are more
likely to intercept lightning strikes than other structures, but do not attract lightning. Lightning
is not more likely to strike houses or cars near a transmission line. Short objects under or very
near a line may actually receive some protection from lightning strikes (PSC Wisconsin 2011) if
transmission poles are taller.
Protected Species
Construction and maintenance of transmission lines may destroy endangered or threatened plants
and animals or may alter their habitat so it becomes unsuitable for them. Trees used by rare birds
for nesting may be cut down or soil erosion may degrade rivers and wetlands that provide required
habitat. Impacts of new transmission lines on wildlife include bird kills from collisions with wires
where previously there were none. Transmission towers make attractive nesting locations for
some larger species of birds, and many are killed each year by making connections between two
or more wires. Some newer designs of transmission towers discourage bird landings to minimize
this occurrence. Impacts on small wildlife stem primarily from disturbing land surface. Some
impacts are short-term and confined to the location of transmission towers; others may have far-
reaching, long-term effects. The most direct effect on small wildlife is destruction or displacement
of species in areas excavated for towers. Mobile wildlife species like game animals, birds, and
predators leave these areas. More sedentary animals like invertebrates, many reptiles, burrowing
rodents, and small mammals may be directly destroyed. If streams, lakes, ponds, or marshes are
filled, drained, or damaged, fish, aquatic invertebrates, and amphibians are destroyed. Food sup-
plies for predators are reduced by destruction of these species. Animal populations displaced or
destroyed may eventually be replaced from populations in surrounding ranges, provided habitat
is restored. An exception could be extinction of resident endangered species.
Many wildlife species are highly dependent on vegetation growing in natural drainages that
may need to be traversed by transmission lines. Vegetation provides essential food, nesting sites,
and cover for escape from predators. Any activity that destroys vegetation near ponds, reservoirs,
marshes, and wetlands reduces the quality and quantity of habitat essential for waterfowl, shore
birds, and many terrestrial species. Small mammals and birds may be harmed by damage to hedge-
rows between farm fields. The habitat requirements of many animal species do not permit them to
adjust to changes created by land disturbance that reduce living space. Some species tolerate very
little disturbance. In instances where a particularly critical habitat is restricted, such as a pond or
primary breeding area, a species could be rendered extinct.
If preliminary research and field assessments indicate rare species or natural communities
may be present in a project area, the utility should conduct field surveys prior to construction. If
a protected or rare species is likely to be in the project area, impacts can usually be avoided or
minimized by redesigning or relocating the transmission line, using special construction techniques,
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