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Surface Armor for Erosion Protection
7.1.2.2 Advantages
A trenchfill revetment allows stabilization along a predetermined alignment, and is
often simpler to design and construct than a revetment placed on the active stream bank.
7.1.2.3 Disadvantages
Trenchfill allows erosion to continue unabated until the stream reaches it, and its
construction requires heavy equipment. Large areas of rights-of-way are usually required.
7.1.2.4 Typical Application
Trenchfill's most powerful use is in the following circumstances:
Where a smooth alignment of the stabilized channel is required (usually to
meet navigation criteria); and
Where rapid erosion rates, high velocities, large depths of flow, or rapid
fluctuations in river stages make construction within the stream channel very
difficult.
Trenchfill has been extremely useful where these conditions exist on the Arkansas,
Red, Missouri, and Mississippi Rivers. The key to successful performance is a relatively
uniform rate of launching at any given point, although uniformity of bank recession along its
length is not a prerequisite to successful performance. Therefore, it is most successful when
bank materials are predominantly noncohesive. Otherwise, additional stone may be necessary,
either during construction or in later reinforcement operations, to compensate for inefficient
launching where the underlying bank material fails by slab or rotational slips.
7.1.2.5 Design Considerations
Special design considerations are as follows:
The required thickness of the stone armor on the upper bank slope can be computed
according to Appendix A or can be based on successful experience under similar conditions.
Stone gradation can likewise either be computed according to the guidance provided
in Appendix A, or based on successful experience in similar applications. A gradation which
has a significant amount of fine stony material has been shown by experience to be effective
in many cases without a filter or underlayment, because the fines fill the voids between the
larger stones, while still allowing the armor layer to retain adequate permeability.  Such
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