Dealing with salinity in Wheatbelt Valleys - Department of Water

George and Coleman
for example in the Central and Eastern Wheatbelt
from Tammin (9.26%) to Merredin (2.3%) (George
1990). These were considered to be an underestimate
of the real extent of salt-affected land.
In 1988, regional hydrologists of the WA Department
of Agriculture estimated areas of salinity and trends
across the state. Anon (1988) describes that in the
Eastern Wheatbelt, where at that time no substantive
evidence of groundwater rise existed (bores drilled
in 1985 onwards had too short a record), salinity
affected only 1.64% (based on ABS 1984 data) of the
area and that potentially 10–20% was at risk. In
1994, with better catchment mapping and longer
groundwater records, Ferdowsian et al. (1996)
indicated as much as 9% of farmland was 'affected'
by salinity to some degree (greater than 50% yield
reduction). They concluded that salinity could
potentially double and then double again (33%)
before coming to equilibrium in approximately 50 to
200 years.
At the time of writing, Land Monitor data from the
Kellerberrin, Perth, Newdegate and Bencubbin
scenes are available for the central and Eastern
Wheatbelt. Each scene represents over 1 M ha, and
covers the area from Toodyay in the west, to
Bullfinch (north-east), Ravensthorpe (south-east),
including a southern boundary near Lake Grace,
Kondinin, Quairading and Pingelly (Table 2). In this
area, 'salinity' has been defined and mapped as land
having 'consistent and low productivity due to
shallow watertables'. It also includes many areas of
primary salinity, but usually excludes heavy barley
grass pastures, saline remnants and lakes (water)
which have been identified by field checking. Field
verified 'commission errors' (overestimates that
include non-saline land) and 'omission errors'
(underestimates of actual saline areas such as thick
stands of barley grass and saltbush) are typically
about 5% and 20% respectively. The process of
ground truthing and statistical analysis has been
described in more detail in each scene report which
is available on the Land Monitor website
(www.landmonitor.wa.gov.au/ – see Caccetta et al.
2000; Caccetta et al. 2000b; Caccetta & Beetson
2000; Dunne & Beetson 2000; Furby 2000).
Table 2: Land Monitor statistics of the area of land classified as having a low productivity attributed to salinity
(includes primary salinity; excludes most barley grass, saltbush, and lakes).
Each scene is based on statistics from different set of satellite data.
Scene/Shire
Shire Area
Ha
Saline 1987–1991
Ha (%)
Saline 1995–1996
Ha (%)
Difference
Ha (%)
Kellerberrin
Merredin 329393 7537 (2.3)* 9138 (2.8) 1601 (0.5)
Bruce Rock 272516 11517 (4.2) 12608 (4.6) 1091 0.4)
Trayning 165196 6750 (4.1) 7577 (4.6) 827 (0.5)
Kellerberrin 191554 11580 (6.0) 11964 (6.2) 384 (0.2)
Tammin 110246 7492 (6.8) 84176 (7.6) 925 (0.8)
Bencubbin
Koorda 283197 41255 (14.56) 42619(15.05) 1346 (0.47)
Dalwalinu 722135 83381 (11.5) 84412(11.69) 1031 (0.14)
Wongan-Ballidu 336518 34232 (10.17) 36587(10.87) 2355 (0.7)
Perth
Cunderdin 186234 13032 (7.0) 13395 (7.2) 363 (0.2)
Northam 143127 2606 (1.8) 2732 (1.9) 126 (0.08)
York 213080 4537 (2.1) 4736 (2.2) 199 (0.09)
Beverly 237118 6296 (2.7) 6663 (2.8) 367 (0.15)
Chittering 121874 538 (0.4) 702 (0.6) 164 (0.13)
Toodyay 169285 832 (0.5) 917 (0.5) 85 (0.05)
Newdegate 1022162 63693 (6.2) 69507 (6.8) 5814 (0.57)
* Percentage of Shire area as defined by Land Monitor.
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