INTRODUCTION (Continued)
Permanent remedial measures to control seepage must consider the type of dam, foundation,
and abutments as a unit. As pointed out for emergency and temporary seepage control
measures, examples given here for permanent remedial measures are for general guidance
only. Actual measures to employ are necessarily dependent on site-specific conditions and
depend on dam and foundation characteristics, reservoir use, and operating history. Most of
the remedies can be adapted to either embankment or concrete dams if found to be suitable to
your specific situation.
MONITORING
In all cases, monitoring seepage is essential, and in some instances may be the only action
necessary.
Monitoring seepage and seepage control measures can lead to a rational conclusion with a
minimum of expenditure. The most common and easiest monitoring is simply to rely on visual
observations and inspections at various intervals and reservoir elevations. Periodic
photographing and videotaping of potential distressed areas can provide valuable
documentation. If the latter monitoring methods are used, it is vital that the camera always be
in the same position to permit easy interpretation.
If not already accomplished during construction, a common recommendation may be to install
instrumentation such as piezometers, observation wells, and seepage collection systems to
determine more definite patterns of seepage behavior.
Review the data on a regular basis to detect any major seepage changes and long-range
trends. If monitoring indicates that a potentially dangerous seepage problem may exist,
consider permanent structural or regulatory measures (i.e. permanent reservoir level
restriction).
If monitoring is selected as a remedial measure, it may also be desirable to consider automated
instruments with predetermined criteria or values to flag undesirable behavior.
LOWERING THE RESERVOIR
The most direct method to reduce or stop seepage is to lower the reservoir and restrict the
reservoir level. Lowering and restriction of the reservoir level may not, however, be an
acceptable permanent solution. Flood inflows may cause the reservoir to rise above restricted
levels, and the benefits of the project will probably be greatly diminished or lost altogether.
If this alternative is selected, care should be taken to lower the reservoir at such a rate so as to
prevent possible flooding downstream and also to reduce the risk of an upstream slope failure
from rapid drawdown.