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| 3 Evaluate site condition data |
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Purpose
The available data should be carefully evaluated to develop a
conceptual understanding of the seepage mechanisms and to identify
factors
that might allow successful measurement. This prevents bias
in the selection of a particular technique that may not be
the most
appropriate.
This step involves interpreting the known information
about the site and provides preliminary assessment of the areas
where seepage is most likely to occur and evaluation of the
likely seepage mechanisms. It will assist in identifying the
conditions
so that appropriate techniques can be selected. Careful evaluation
may lead to a concentration of effort into a particular location;
redefinition of the scale of the seepage investigation.
Inputs
Maps, site condition data, observations of seepage, anecdotal
information
For this task, existing information is usually adequate,
although if necessary some field data may be needed to
assess the basic
factors that might affect channel seepage.
Areas with characteristics that indicate channel seepage
are assessed. This involves evaluation of information
to interpret possible seepage
mechanisms and identify likely high-seepage locations.
In particular:
- Features such as the distribution of highly permeable
materials, rock zones with fracturing or potential fracturing,
or extensive
clay intervals
- Anecdotal information and observations
of leakage
- Distribution of any silt layers in the channel floor
- Groundwater
depth and salinity
| Responsibility/decision
makers |
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Ideally undertaken by the project engineers. For specialised
information, such as interpretation of existing
aerial photos and some subsurface
data analysis such as geophysics, specialists should
be involved.
| Output |
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The four main outputs are:
- Basic knowledge of the material and water characteristics
that are important in selecting a measurement
technique
- Identification of areas that may be targeted
for detailed testing, such as locations
for pondage tests
and drilling.
- Understanding of the seepage
mechanisms
- Understanding of the scale of the seepage
investigation, i.e. local or intermediate
to large
Information obtained from field investigations
as part of the seepage measurement program
(e.g. drilling
information,
groundwater
levels)
may also contribute to further investigations
of site characteristics.
Local-scale recommendations
[Up to approximately 400m in length] |
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It is recommended that a proper assessment of
what is known is conducted, even if a process
of evaluating
data
has
already been
performed formally
or intuitively.
Intermediate to large-scale recommendations
[Hundreds of metres to tens of kilometres
in length] |
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Intermediate to large-scale investigations require
evaluation of site condition information including:
- Geological and soil data
- Groundwater water levels and salinity
- Lateral seepage occurrences
In large-scale studies this information needs to be understood
because of possible variability along the section
of interest. This can effect
extrapolation from test sites to the entire
section of channel. Therefore mapping of the conditions along
the channel, preferably
using a GIS
application, is a valuable activity.
| Related
pages |
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Previous: 2 Collate
site data
Next: 4 Select seepage measurement techniques |
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