Construction of Stabilization Works
Ecologically sensitive periods such as spawning and nesting should be considered in
the timing of construction. This is particularly compelling if threatened or endangered species
are involved. A potential difficulty is that nesting sites may not be known at the time a
contract is issued, in which case the specifications should provide for a conflict resolution
procedure that will be environmentally sound, but that is also fair to the contractor. A
contract modification and extra payment may be necessary if construction operations are
significantly disrupted by unforeseen circumstances. An example of a species-specific
approach used by the U.S. Army Corps of Engineers on the Sacramento River, California, for
sites at which bank stabilization work could not feasibly be performed before or after bank
swallow nesting season, was to cover the bank with plastic sheeting prior to the nesting
season. This forced the swallows to nest at other suitable sites not scheduled for bank
protection.
It is advisable to consult with appropriate agencies, organizations, and environmental
experts to define the construction practices that are required or recommended for a particular
region.
10.4 SPECIALIZED CONSTRUCTION PROCEDURES
The impact of construction procedures on project economics and the selection of a
bank stabilization method was discussed in 5.3. This section presents some specific
construction approaches that may result in a more efficient and effective job. These
approaches are discussed under the following headings:
Access for construction equipment;
Sequence of construction;
Subaqueous placement of stone or similar materials; and
Procedures for proprietary products.
10.4.1 ACCESS FOR CONSTRUCTION EQUIPMENT
On small streams, the choice of access is a matter of weighing the trafficability,
environmental impacts, and real estate aspects of alternate routes. Fortunately, the most
trafficable route often has the least environmental impact. In some cases, the streambed,
especially sand and gravel bars, may be suitable for maneuvering of construction equipment.
The environmental impact may be acceptable, especially if the need for clearing of vegetation
along the streambank is reduced. On streams with high bed material transport, the next flow
event will likely obliterate any traces of construction activity in the streambed. However, it
is advisable to be prepared to provide alternative access, because rapid increases in
streamflow or undetected areas of "quicksand" can be hazardous to streambed operations.
On navigable streams, the use of floating plant expedites construction and reduces
costs and environmental impacts, and on larger streams is in fact the only feasible way to
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