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Subsurface characterisation
Subsurface characterisation of the area around a channel
provides information on which assessments of the sites of
seepage can be made. The techniques to consider are Soil
and geological profile classification and Groundwater
assessment, including water-level monitoring, mathematical
modelling and hydrochemical investigations
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Soil and geological profile
classification: summary
Pages in this section include:
This page provides a summary of the soil and geological
profile classification channel seepage identification
and measurement technique.
Principle
Soil type is one of the most influential variables affecting seepage
rate. Using soil and geological information to assess actual or
potential seepage assumes that seepage is primarily a function
of hydraulic conductivity, which is in turn a function of the soil
texture.
More information
| Method |
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Subsurface profiling of soils and geological conditions
can be conducted in a channel seepage investigation
for various reasons, including:
- As part of site characterisation
- To help define seepage
mechanisms
- To assign seepage rates to soil types and estimate
seepage through changes in soil type
Limited soil and geological profiling can be
undertaken by review of available data from
soil and geological
maps. Subsurface profiling on a site-specific
basis requires site inspection, local mapping
of soil
types and drilling.
Key issues in developing a drilling program
for a channel seepage investigation are where
and
how many bores to drill, type of drilling to
use, what
depth to drill to, and how to log recovered
materials.
More information
| Applicability |
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Using soil and geological profiles in channel seepage
investigations provides a picture of the conditions
under which seepage is more likely to occur. On its
own, a geological profile will not provide estimates
of seepage rates.
Estimating losses based on application of a seepage
rate for a given soil type is a useful method for providing
an estimate of zones of seepage loss from a system.
Care should be taken in interpretation, in that:
- Seepage rates can vary significantly
within one broad soil type.
- Multiple measurements
are required to obtain a reliable estimate of mean
hydraulic conductivity of a
particular soil type.
- Some significant factors influencing seepage
are not allowed for (e.g. groundwater levels, clogging
layer at channel surface)
More information
| Practical
implementation |
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Regional-scale maps are readily available over most
areas to obtain general knowledge of site soil and
geological properties. However, care has to be taken
if investigations rely only on these maps because of
the details of map scale.
- Drilling of soil
investigation bores should be undertaken with: suitable
drilling equipment, able
to penetrate
to the required depth.
- Qualified drillers, preferably
with knowledge of local conditions should be
used
More information
| Indicative costs |
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Costs of drilling of soil bores vary considerably depending on
the type of drilling contractor and drilling rig used, and whether
an additional person is on-site for logging of the bores.
For estimating purposes, a rate of $40-50/m for soil bore drilling
can be used. Costs for groundwater observation costs range from
$70-120/m (excluding mobilisation).
More information
| Related
pages |
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For a more detailed description of the soil and geological profile
classification technique see:
Soil and geological profile classification:
principle, method
Soil and geological profile classification:
applicability, practical implementation, experience from the
trials, indicative costs |
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