Purpose
To assemble and map data including groundwater
depth and quality, channel depth and capacity, evidence of seepage,
and information about channel alignment, elevation, construction and maintenance.
Inputs
Understanding
of the factors that affect channel seepage using sources
of these data including published or unpublished
data from local
government agencies or agencies such as the Murray
Darling Basin Commission (e.g. the Basin in a Box map series).
Organisational
knowledge of the channel dimensions and distribution.
At the early stages of
an investigation, fieldwork is usually not necessary,
although in the absence of any data, or if there is conflicting
data,
some investigation
work such as drilling may be needed.
The above information is best assembled by mapping the key
factors along the channel length. Maps can be developed
displaying key
factors likely to affect detection and measurement of
seepage, including:
- Soils and geology
- Groundwater depth and quality
- Channel depth and capacity
- Visual observations of seepage
Fieldwork is not necessary to develop these
maps, however the finest scale (covering the selected length) and
best quality
existing data should be used. Preparation of the maps in GIS format is
valuable
as they can then be used for later analysis with
other data sources. Channel alignment is required on the maps.
Distribution of silt layers at the base of channels should be documented.
If channel cross-sections are prepared,
silt layer
thickness should
be indicated. Further important information to be collated includes:
- Channel elevation compared to surrounding natural ground
levels, including the full supply level
and design levels
- Channel construction and maintenance data
| Responsibility/decision
makers |
 |
Generally project officer level.
| Output |
|
Information about spatial distribution of key factors affecting
channel seepage, including a summary of what is known
and not known about the channel and seepage conditions, and additional
information that might be required.
Local-scale recommendations
[Up to approximately 400m in length] |
|
Before decisions for action to are made, there needs to
be information collated about the site conditions.
Details include
soil types, channel characteristics and evidence
of seepage. This information
might be
the basis for the investigation in
the first place.
If there are no details other than an inferred
seepage problem, key data should
be collated. If necessary,
additional site
data, such
as soil information and depth to
watertable should be collated. They should also be reflected
in the project objectives.
Intermediate to large-scale recommendations
[Hundreds of metres to tens of kilometres
in length] |
|
Information on depth to groundwater,
background groundwater salinity,
soil type and channel
hydraulics should
be known or gathered,
both for the site where the testing
is conducted, and over the area for
which the results are to be extrapolated.
In the initial stages
information should be sufficient to propose a conceptual
model of
the seepage
mechanism, to detect
where
changes in these parameters may impact
on the mapping technique, and to
assist in technique selection. Hydraulic information
is required to help determine potential
channel
seepage
mechanisms.
| Related
pages |
|
Previous: 1 Define
Objectives
Next: 3 Evaluate site condition
data |
