Monitoring and Maintenance of Stabilization Works
Significant changes in bed material composition in the project reach can affect the
performance of the work, either favorably or unfavorably. For example, an increase in the
amount or size of gravel in the bed may limit bed scour, but may also cause changes in
planform which could adversely affect the work. Changes in bed material can be monitored
either informally by detailed visual observation and photographic documentation, or through
a formally designed sampling and analysis program. A formal program is not likely to be cost-
effective solely for monitoring the protection work itself, but may sometimes be justified as
part of a broader study.
11.2.3.4 Hydraulic Data
Initial collection and analysis of essential hydraulic data will presumably have been
done in planning and design of the protection work. Hydraulic monitoring should concentrate
on those parameters which were identified during planning and design as being most critical
to the adequacy of the work. Over the short-term, routine monitoring of hydraulic
parameters will usually not provide a basis for changing design criteria that are based on
longterm probabilities, but it may provide an indication of whether or not design assumptions
were reasonable.
Velocity is usually the most critical element for riprap protection. Also, if the
alignment of flow into the protection work is changing significantly, the effect on the
curvature correction factor for riprap design velocity should be evaluated.
Hydraulic data in the form of long-term stage-discharge relationships can indicate
whether streambed degradation is cause for concern. These observations are best made at
stations downstream of the project, so that degradation can be detected in time to reinforce
the toe of the work or take other remedial action if necessary.
11.2.3.5 Geotechnical Data
The degree of geotechnical monitoring required is highly site-specific. A simple rule
is that if critical geotechnical parameters cannot be monitored visually, then sophisticated
devices such as piezometers and slope indicators may be required, especially if there was
some degree of uncertainty in the original design, or if the consequences of failure would be
high. In other cases, a visual inspection for proper function of internal drains, surface
indications of slope settlement, and similar items may be sufficient.
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