Dealing with salinity in Wheatbelt Valleys - Department of Water

George and Coleman
advantages of solar ponds over other alternative
energy systems is that there is a degree of energy
storage intrinsic to the operation. That is energy
generated during the day will be stored at least
through the night. Compare this with wind or solar
energy, which suffer from the vagaries of wind
strength and diurnal light. It should also be possible
to predict the energy production for a period in
advance. Both of these points are important
management considerations in the use and
conservation of energy. In Australia, solar ponds
operate in central Australia and a 0.3 ha experimental
pond is being constructed in Victoria (Pyramid Hill).
There are advantages to match solar pond energy
with desalinisation. Disposal of waste brine from a
desalinisation unit can be used in the solar energy
plant. It has been estimated that a ten-hectare solar
energy salt pond will generate 200,000 KWh of lowgrade
energy ($130,000) per year in northern
Victoria at a capital cost of $300,000 (Akbarzadeh &
Earl 1992). The operating costs have not been
stated but they would be significant and in the same
magnitude as the energy replacement cost.
A comprehensive extraction scenario is possible and
could be a profitable method of extracting and
disposing groundwater in an environmentally
sensitive way. The aquaculture would be the most
profitable, at least in the short term, although
significant time, money and effort would be needed
to create a synergistic project. The reality is also that
the mineral extraction processes require a massive
input of brine to be profitable. For instance,
profitable salt production would need an annual
production of 15,000 tonnes (~750ML of seawater)
or more. It is possible to be profitable with less
production by targeting niche markets, but these
markets are limited. Standard SAL-PROC processes
require even more brine to generate a viable
business and estimates place the brine supply for a
viable production plant at more than 2,000 ML per
annum. However SAP-PROC PSP plants, portable
systems capable of extracting salts from brine stores,
may provide a viable alternative for smaller pumping
systems (e.g. rural towns). It is currently not known
whether these small plants are profitable, but they
do provide a useful method of removing salt in an
environmentally sound way that may be cost neutral.
The transition from resource to product depends on
the ability of the producer to convert the resource to
another commodity. This is an important distinction
as all too often a resource is described in favorable
terms, when in reality producing a marketable
product is much more difficult. For instance salt is
– 14 –
readily produced using the lowest input of
technology; it happens naturally on farmland after all.
The marginal cost of salt from a medium size
producer is about $A5–10 per tonne. Quality salt
can be bought in bulk for less than $A60 per tonne.
The market for salt is for a product that is over
99.9% pure and of a particular size. To achieve this
purity the salt must be processed mechanically and
the crystals must be very robust. Experience has
shown that the larger purer crystals have the best
chance of being commercially viable. Some
processes generate a better chemical quality product
such as some natural lakes and the SAL-PROC
process, but the crystals still require cleaning and
drying. Given these low values any cost or loss
through processing can rapidly make a product noncommercial.
DISCUSSION
Salinity management
Both in situ rainfall and lateral flows from tributary
sediments and hillslope aquifers recharge wheatbelt
valleys. The relative mix and influence of these
sources on the extent of salinity is both spatially and
temporally variable. However it is apparent from
several studies (McFarlane et al. 1989; George et al.
1991; Salama 1997) that farmers who principally
manage recharge to valley sedimentary aquifers, have
a chance of mitigating the impacts of salinity on their
property by acting unilaterally.
Management options for salinity have recently been
tested using numerical models (as field verification is
extremely difficult and requires a longer-term
commitment) and by review of existing field
examples. George et al. (2001) showed from use of
the Flowtube model that recharge reductions of
greater than 50% were required to significantly alter
the likely rate of watertable rise in most wheatbelt
type (low gradient) catchments. In many examples
however (e.g. alley and phase farming with a
perennial such as lucerne) reductions of this
magnitude only reduced the rate of rise, thereby
buying time, but did not substantially reduce the
potential risk. Of the options tested, only
engineering provided significant potential long-term
impacts for valleys. While large plantations within
valleys may potentially create temporary reductions
in the rate of watertable rise, high groundwater
salinities and unfavorable soils represent significant
limits to effectiveness of this option. The relative
impact of a range of modelled treatments is
summarised in Figure 2.