Selection of Site-specific Stabilization Techniques
proximity to populated areas. Proximity to populated areas might restrict operations by
public objections to dust, noise and vibrations, and concern for potential safety hazards to the
public. These problems should be identified early in the selection process so that time is not
wasted considering impractical techniques.
5.3.3 FEASIBILITY OF INCREMENTAL CONSTRUCTION
The cost of a stabilization project and/or the initial investment can sometimes be
reduced by constructing the project in vertical or horizontal increments. It should be noted
that the distinction between a planned incremental approach, and having to do additional
work later because the original design was inadequate, can become blurred. The distinction
is that an incremental approach is planned, and is implemented with the desired result,
whereas doing additional, unexpected work is both unplanned and unwelcome.
5.3.3.1 Vertical Increments
This approach consists of utilizing for the first phase a method which will induce
deposition of sediment within the protection works, then taking advantage of that deposition
to construct the remainder of the work at a reduced total project cost.
This approach requires flexibility, both in funding and in timing of construction, but
can be very useful and economical. It can reduce the required height of retards and retaining
structures, permit the planting of vegetation at the ideal season for growth, allow the
introduction of vegetation at the ideal time to take advantage of induced deposition, and
incorporate the use of vegetation to induce more deposition. It also spreads the expenditure
for construction over a longer period of time.
This approach is feasible only if:
An indirect protection technique is suitable for the site. A possible exception
to this condition is the use of armor protection on the lower bank, with
vegetation to be established on the upper bank during the ideal planting
season, after the upper bank has eroded to a flatter slope more conducive to
bank preparation and planting of vegetation.
The bank instability is moderate, so that a delay in completion of the work will
not endanger the initial work or the object of the work.
A variation of this approach is to plan for reinforcement of the toe of the work after
initial toe scour occurs. This approach requires careful monitoring of the work so that the
reinforcement can be placed before toe scour progresses to the point of failing the upper
bank.
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