The objectives of seepage remediation need to be determined in
order to select an appropriate remediation technique.
Objective of seepage remediation
Primary objectives of seepage remediation works may include:
Conservation of water
Reducing the impact of seepage (eg salinity and waterlogging)
A combination of both
If the objective is conservation of water or a combination
of the above objectives, channel lining is appropriate. If
the objective
is to reduce the impact of the seepage, groundwater intervention
techniques such as pumping, core trenches, tile drainage
or vegetation should be considered.
Secondary aspects of remediation that may affect the selection
of a technique, include:
Reduction of channel dimensions and excavation costs
for new channels
Increase in capacity by improvements
in hydraulic efficiency
Stabilisation of banks from
erosion
Reduction of operation and maintenance costs
by refurbishment of ageing or deteriorated assets.
Consideration of future supply requirements
Potential for Other Asset Management Options
In determining the objectives of seepage remediation, consideration
should be given to other asset management options that
could be an appropriate response to channel seepage.
These include remodelling or relocating the channel,
or rationalising the channel if downstream supply of
water is no longer required. Another option is to do
nothing, should the impact of seepage be small or the
not cost effective to remediate.
Extent
of seepage reduction required
The purpose of remediation is to reduce seepage to an acceptable
level at a justifiable cost. The benefits of remediation,
such as water savings and reduced waterlogging or salinity,
will
influence both the required seepage reduction and the
economic basis for
selection of a lining method.
A more expensive lining may be justified economically
if it can reduce seepage to a very low level. However,
a less
expensive
lining
may provide an acceptable seepage rate reduction. The
permeability of a lining depends on its properties and
also the presence
of any flaws caused during manufacture or installation.
No channel
lining is completely impervious. Indicative permeabilities
of liner types are given in the table below.
Table 1 Indicative lining permeabilities
Type of lining
Expected seepage rate reduction
Indicative liner permeability (L/m2/day)
Geomembrane
85-95%
0-0.5 but varies
Concrete
70-95%
Below 0.5 if well constructed and maintained
Bentonite lining
60-70%
0.5-1.0
Chemically stabilised soil
60-90%
0.5-1.0 but varies widely with material used
Compacted earth
70-90%
0.5-2.0 but varies widely
Unlined - ordinary clay loam
5.0-25.0
Source: Construction and Refurbishment of Earthen Channel
Banks (G-MW), May 2003.
Target seepage reduction rates for a length of channel
can be achieved by selectively lining sections with higher
seepage
rates. This
presumes that areas of higher seepage rates can be identified.
See Identification and measurement.
