Dealing with salinity in Wheatbelt Valleys - Department of Water

Pannell
Table 1: Summary of economic analyses of salinity management for six towns in the Rural Towns Program
Town
(timescale of
estimates)
Timing of onset
of major costs
Damage costs from
salinity if no works
undertaken
Total cost of
possible works to
control rising
groundwater
Potential gain from
engineering works
(years) ($ million) ($ million) ($ million)
Brookton (60 years) 4 0.62 0.28 0.34
Corrigin (60 years) 2 0.21 -0.10 0.31
Cranbrook (60 years) 22 0.61 2.3 to 5.7 -1.6 to -5.1
Katanning (30 years) 1 6.9 7.6 -0.74
Merredin (60 years) 26 0.38 1.8 to 4.6 -1.4 to –4.2
Morawa (30 years) 1 0.25 0.90 -0.65
The final column shows an estimate of the net
benefits of strong intervention in the towns, based
on an assumption that it would result in prevention
of all costs listed in the third column. It is striking
that in four of the six towns, the economics of the
engineering interventions studied appear adverse.
The two positive results, Brookton and Corrigin,
have the advantage of being able to make some
valuable use of the pumped water. Even in
Katanning, which is probably the most saltthreatened
town in Australia, the costs estimated
for disposal of pumped saline water into lined
evaporation ponds is so high that it roughly cancels
out all the benefits from salinity prevention. If it is
difficult to economically justify lined evaporation
basins to protect the extreme example of
Katanning, it seems unlikely that this approach
could pay off in any less extreme cases.
In the case of Merredin, the consultants concluded
that “the actions warranted for immediate
implementation include advice with water
management to reduce recharge and damage to
infrastructure, continual improvement in drainage
systems, and tree planting within the town to
reduce recharge,” (Dames & Moore – NRM 2001,
p.13).
Other infrastructure
It was noted above that the biggest costs incurred
in salt-affected towns are from damage to roads.
Roads outside towns will also be affected. Dames
& Moore – NRM (2001) based their road costings
on a report of the Murray Darling Basin
Commission (1994), which reported, for example:
– 7 –
• The average life of sealed roads in Victorian
irrigation areas with water tables of 2.0 m or
less was 20 years, compared with 40 years for
equivalent roads in dryland areas over deep
groundwater tables.
• When replacing major highways, the additional
cost in situations with shallow groundwater
(less than 2.0 m) was around $100,000 per
km, on top of the normal construction cost of
around $400,000 per km. Repair costs for a
major highway due to shallow groundwater
(i.e. the cost of patching and repairing the
road to maintain the pavement condition) was
$10,000 per km per year.
• For a standard sealed country road, estimated
construction costs were $100,000 per km,
plus $25,000 to $35,000 in locations with
shallow watertables. Additional maintenance
costs due to shallow water tables would be
$400 to $2,900 per km.
• For gravel roads, the construction cost was
$7,000 per km plus $3,000 for shallow water
tables, with annual maintenance increased by
$200 per km for shallow watertables.
Campbell et al. (2000) estimated that for the
Great Southern region of southwest Western
Australia, 1,200 buildings (15% of all buildings in
the region), 3,300 km of roads (26%) and
16,000 farm dams (44%) face the risk of damage
or destruction from salinity. No similar study has