Selection of Site-specific Stabilization Techniques
modification is appropriate, a smoother alignment is generally preferable hydraulically and
structurally, but an irregular alignment will provide more aquatic habitat diversity.
The most feasible methods if a realignment is necessary are trenchfill or windrow
revetment, dikes, and retards.
This topic is discussed further in Sections 5.1.7 and 6.1.2.
5.1.6 IMPACT ON FLOWLINES
By altering the channel geometry, and in some cases the channel alignment and length,
a streambank stabilization project will change the hydraulics of the flow somewhat. Because
the changes are often insignificant, and/or obscured by other factors, such as upstream
reservoirs, channelization, or changes in basin land-use, a reliable quantitative assessment of
the potential impact of the project on the elevation of the flowline for a given flow may not
be possible. However, the sensitivity of potential impacts to the various assumptions that
must be made regarding the effect of alternative stabilization methods on channel hydraulics
can be examined, and the range of potential impacts can be defined. Fortunately, for most
bank stabilization projects which are limited in scope, even pessimistic assumptions will
indicate no significant impacts.
Significant lowering of flowlines may have the following undesirable impacts:
Channel degradation on tributaries;
Reduction in amount of aquatic habitat at low flows;
Lowering of ground water level adjacent to the stream;
Decrease in geotechnical stability of channel banks;
Encroachment of vegetation into the channel;
Increase in harbor dredging requirements; and
Disruption in the operation of riverside facilities.
The most severe cases of lowering of stages are usually associated with
channelization, and the impacts of bank protection alone may be insignificant, and impossible
to determine precisely.
5.1.6.1 Flood Flows
On any stream where flooding is a potential problem, but especially on flood control
channels or small streams, the potential impacts of a stabilization project on channel
conveyance must be carefully considered.
An armoring approach would not be likely to reduce conveyance. In fact, any armor
method is likely to be hydraulically smoother than an existing eroding bank, especially since
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