Environmental Engineering Reference
In-Depth Information
or limiting the time of construction to specific seasons. In some limited cases, right-of-ways can
be managed to provide habitat for endangered or threatened species, such as osprey nesting plat-
forms built on top of transmission poles where wires are far enough apart to avoid contact (PSC
Wisconsin 2011).
Water Resources
Construction and operation of transmission lines across creeks, streams, rivers, and lakes may
have both short-term and long-term effects. Water quality can be impacted by work within a lake
or river and by nearby land clearing and construction activities. Removal of nearby vegetation
can cause water temperatures to rise and negatively affect aquatic habitats. It can also increase
erosion of adjacent soils, causing sediment to be deposited into a water body, especially during
rainfall. Construction often requires building temporary bridges across small channels, which if
improperly installed may damage banks and cause erosion. Overhead transmission lines across
major rivers, streams, or lakes may have a visual impact on users and pose a potential collision
hazard for waterfowl and other large birds, especially when located in a migratory corridor (PSC
Wisconsin 2011).
Some waters are characterized as being valuable or unique for various features including fish-
eries, hydrology, geology, and recreation. Regulations require that these shall not be degraded
in quality without good justification. By assigning these classifications to specific streams, high-
quality waters receive additional protection from point source pollution. Degradation of trout
habitat is caused by siltation from erosion and drained wetlands, among other factors. Impacts to
surface waters can be avoided by rerouting a transmission line away from a water body, adjust-
ing pole placements to span the water resource overhead, boring a line under a water resource, or
constructing temporary bridge structures across it. Methods to minimize impacts include avoid-
ing pole placements adjacent to water, using approved erosion control methods, using alternative
construction methods such as helicopter construction, landscaping to screen poles from the view
of river users, and maintaining shaded stream cover (PSC Wisconsin 2011).
Several methods and cable types are available for constructing a transmission line under a
water resource. Directional boring of holes under waterways for lower-voltage transmission
and distribution lines is common. High-voltage lines are rarely constructed underground due to
substantial engineering, dollar costs, and operational hurdles that would need to be overcome for
underground construction to be a feasible alternative to overhead construction. Constructing a line
underground minimizes construction and esthetic impacts to a water resource. However, it does
require potentially large construction entrance and exit pits on either side of a water body. There
is also potential for contamination by drilling fluids into a water body and subsurface environment
(PSC Wisconsin 2011).
Use of properly designed temporary bridge structures avoids driving construction equipment
through streams. Temporary bridges may consist of timber mats that allow heavy construction
equipment to cross streams, creeks, and other drainage features without damaging the banks or
increasing the potential for soil erosion. Temporary bridges should be located to avoid unique or
sensitive portions of waterways, like riffles, pools, and spawning beds. Proper erosion control is
necessary for all construction activities, especially those that may affect water resources (PSC
Wisconsin 2011).
Woodlands and shrub or scrub areas along streams are a valuable buffer between farm fields
and corridors of natural habitats. Vegetation maintains soil moisture levels in stream banks, helps
stabilize banks, and encourages diversity of wildlife habitats. Removal of vegetative buffers from
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