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Direct and point seepage measurement techniques
The techniques considered most likely to provide accurate
measurements of the rate of seepage are direct measurement
techniques, which include inflow-outflow
tests and
pondage tests. In
addition, point measurement tests provide a way of
quantifying seepage rates at specific locations in a channel.
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Point measurement: summary
Pages in this section include:
This page provides a summary of the point measurement channel seepage
identification
and measurement technique.
Principle
A point test measures seepage at a given point. This usually involves
the application of water to the surface or hole within the channel,
and measurement of the rate of water loss.
More information
| Method |
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Point measurements can be undertaken either when the
channel is operating or when it is not running,
depending on the particular technique used.
To obtain a broad coverage of the infiltration
variability many point measurements are usually required.
In Australia, the most commonly used techniques
are those for which equipment and experienced
operators are available. These are:
- Idaho seepage meter (operating
channel)
- Ring infiltrometers (channel empty)
- Disc
infiltrometers (channel empty)
More
information
| Applicability |
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Point measurements are not sufficiently reliability
for absolute quantification of channel losses
and are best suited for determining the distribution
of seepage losses (relative seepage), and
then generally over short lengths of channel
(e.g. defining a hotspot).
- They are generally not reliable
for direct (absolute) quantification
of channel seepage
losses due to the variable nature of
soil and channel beds.
- Typically a high
percentage of seepage occurs through
a relatively small percentage
of the channel, so numerous point measurements
are required to obtain a reliable estimate
of the mean.
- To obtain reliable and
meaningful results, tests require a skilled
operator or
technician.
- They are not practical for a post-remediation
assessment, other than for clay-lined
channels.
More information
| Practical
implementation |
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Seepage meters should be installed with
the least possible disturbance of the
bed material.
Many measurements are required to obtain
a reliable estimate of the mean, so the
point test method requires a large number
of tests to obtain a representative seepage
rate over a given length of channel.
More information
| Indicative
Costs |
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Point measurement techniques should be
conducted by an operator with expertise
in the equipment being used. The greatest
variable influencing the cost of point
measurement is the density of testing.
Subcontractor costs for infiltration
tests conducted during the IAL study
are provided as a rough guide to cost
estimation:
Idaho Seepage Meter - 22 sites (4 individual
tests at each site, over the channel
cross-section): $6,200.
Ring Infiltrometer: 29 individual tests:
$5,000.
Disc Permeameter: 24 individual tests:
$4,000.
More information
| Related
pages |
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For a more detailed description of the point measurement technique
see:
Point measurement: principle, method
Point measurement: applicability, practical implementation, experience
from the trials, indicative costs |
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