2.1.1 Climate
The catchment experiences a typical Mediterranean
climate of hot dry summers and cool wet winters.
Summer has a range from 33˚C in February to 18˚C in
July with a mean average temperature of 32.2˚C. Winter
has a range of 18˚C in February to 8.2˚C in July with a
mean average temperature of 7.0˚C.
Average rainfall for the southern portion is 800mm/yr
decreasing to less than 600mm/yr in the northern regions
(Bureau of Meteorology, 1998).
Most water courses in the catchment flow during the
winter months and have reduced or no flow during the
summer months. Weather patterns typically have strong
easterly to north-easterly winds in the morning and
south-westerly in the afternoon during summer with
thunderstorms and lightning common. During winter the
winds come from the northwest to southwest.
2.1.2 The river, major tributaries and wetlands
The Brockman River flows south along the western edge
of the Darling Plateau through a deeply incised valley to
join the Avon River between the Walyunga and Avon
Valley National Parks. The Wannamal Lake system to
the north, and seasonal streams flowing from the east
and west, drain directly into the Brockman River.
The Wannamal Lake system is listed as a culturally and
ecologically significant wetland (Environment Australia,
2001). Analysis of water quality readings (J. Lane,
CALM, pers. Comm.) since 1978 indicate that salinity in
the lake is increasing (figure 3). Anecdotal information
at the time of settlement in the area during the 1890’s
indicates that the water was fresh enough to support
vegetable gardens and fruit trees (Buchanan, 1996).
Observations made by long time residents of the area
suggest that during the early 1950’s the water was
relatively fresh and that good clover pastures grew in
nearby paddocks that are now bare salt scalds (Pers.
Comm. D. Purser). A suite of smaller lakes and wetlands
to the west, including Lake Bullingarra, are still fresh.
2. What we have in the Brockman
River catchment
Figure 3: Salinity and depth of Lake Wannamal recorded in spring 1979-1998. (J. Lane, CALM)
Sep-79
Sep-80
Sep-81
Sep-82
Sep-83
Sep-84
Sep-85
Sep-86
Sep-87
Sep-88
Sep-89
Sep-90
Sep-91
Sep-92
Sep-93
Sep-94
Sep-95
Sep-96
Sep-97
Sep-98
Salinity (mS/cm)
Depth of Lake (m)
Date Sampled
- Salinity
- Depth
2.2
Water and Rivers Commission
Natural Resource Management Plan for the Brockman River Catchment
The township of Bindoon is situated on the Brockman
River where it flows into Lake Needoonga, part of the
Chittering Lake system and a listed significant wetland
(Environment Australia, 2001).
In 1975, CALM constructed a weir at the end of the
Chittering Lakes Nature Reserve to control the levels of
Chittering and Needoonga lakes. The gates in the weir
regulate the flow of water and the depth of the lakes.
The weir was installed after a drain was constructed that
caused the lakebed to drain prematurely, impacting on
the bird-breeding season.
The aim of the water management is to achieve a
desirable water level in the lake throughout the year. The
lake should be dry from mid-March to the opening rains
and the more saline waters that accumulate during mid to
late summer should not be released downstream in an
uncontrolled manner (P. Dans, pers. Comm.). Thus,
during the summer months, only the catchment south of
the weir contributes to the water flow in the Brockman
River.
The water levels in Lake Chittering are managed for:
• Wildlife management to sustain the lake vegetation
survival and regeneration and the annual bird
breeding season;
• The farming industry to avoid excessive flooding of
adjoining agricultural land, and;
• The horticultural industry to avoid releasing
excessively saline waters down the Brockman River
that adversely impacts the opportunity for farmers to
irrigate horticultural crops.
Guidelines have been developed to ensure the
requirements of conservation, neighbours and
downstream users are all considered (CALM, 1999).
2.1.3 Landforms, geology, & soils
The Darling Plateau, an ancient landmass worn down by
erosion, underlies most of the eastern portion of the
Brockman River catchment. To the west, the catchment
extends over the Dandaragan Plateau. A major regional
fault line, the Darling Fault, separates these two
geomorphic regions.
The Darling Plateau
The Darling Plateau is made up of two major rock
sequences. The first sequence is a 10-km wide belt of
crystalline rocks referred to as the Chittering
Metamorphic belt. Intense erosion within the Chittering
Metamorphic belt has produced a major north-south
trending valley system in which the Brockman River
flows south. The second sequence to the east is granitic
rock covered with a lateritic cap referred to as the
lateritic uplands(Wild and Low, 1978). Laterite is
sometimes referred to as ironstone or coffee rock.
The deeply incised Chittering Valley is characterised by
dissected, steep slopes and domed granite outcrops high
in the landscape with variable and complex soils. Parent
materials may be weathered or unweathered gneiss,
granite or dolerite or may occur as colluvium. Colluvial
lateritic material from the plateau surface may extend
down slope. Yellow duplex and brown duplex and
gradational earths are the most common soils. Generally,
the yellower soils are associated with the granite, and the
red and brown soils with dolerite dykes (King and Wells,
1990). Loamy soils, now extensively cleared for
agriculture, are found on the lower valley slopes and
floodplain.
The lateritic uplands are typified by undulating,
dissected land surfaces with rubbly, pale orange lateritic
soils and pea gravels. Red alluvial, clay soils
characterise the valley floors while upland remnants of
the plateau surface form higher land with sands and
sandy gravels interspersed with laterite outcrops. Saline
soils occur within the valley floors.
Most of the area outside reserves is cleared for
agriculture with small pockets of native vegetation
along fence lines and watercourses. Gully erosion is the
predominate erosion hazard but landslips have occurred
on the steeper slopes of the Chittering Valley.
The Dandaragan Plateau
The Dandaragan Plateau to the west of the Darling Fault
is a wedge shaped erosion remnant of the Perth Basin
with sediments covered by recent deposits of sand and
laterite (Wild and Low, 1978). Sandplain features
dominate the landscape with broad U-shaped valleys,
sand-filled drainage lines and some breakaways. The
soil pattern is closely related to topography
(Churchward, 1980). Brown deep sands, yellow deep
sands, pale deep sands, sandy gravels and shallow
gravels are dominant, with red deep sandy duplex soils
on the valley floors (Moore, 1998).
Soil landscapes are outlined in the Shire of Chittering
Land Capability and Management Study prepared by
2.3
Water and Rivers Commission
Natural Resource Management Plan for the Brockman River Catchment
Land Assessment Pty. Ltd. Part 1 – Working Paper. A
summary appears in Appendix 1.
2.1.4 Native vegetation
Field studies of the distribution of vegetation complexes
in the Brockman River catchment were completed using
existing vegetation maps produced as part of the System
6 study (DEP). The extent and condition of native
vegetation in the catchment is shown in figure 4 and
summarised in table 1. Native vegetation covers
approximately 770 km
2
, or 51% of the total area of the
region (1,520 km
2
). The greatest area of native
vegetation occurs within the western forest/woodland
and eastern heath regions while the central area consists
of severely dissected remnants within an agricultural
landscape. These areas have been heavily cleared and
now the remaining remnants are generally small and
dispersed.
Approximately 201 km
2
(13%) is reserved for
conservation purposes with much of this conservation
land being confined to the eastern Darling Scarp forests
and north-western sandplain. The landuse and number of
vegetation remnants in the Brockman River catchment is
outlined in table 2 and figure 5. Size class of remnants
by landuse is shown in table 3.
Twenty System 6 vegetation complexes are recognised
in the catchment and are shown in figure 6. Figure 7 and
table 4 show the remnant vegetation complexes
represented now and the spatial extent of vegetation
complexes pre and post clearing and currently reserved.
One complex (Williams-Avon-Brockman-Mumballup
Complex) has less than 20% remaining of its original
area, while twelve complexes have less than 10% of
their original extent reserved. The complexes that
remain best represented occur in the east and northwest,
and correspond to the greatest areas of remnant
vegetation (Connell and Ebert, 2001).
Heddle et al (1980) identified vegetation complexes for
each of the soil landform associations defined by CSIRO
(Churchward and McArthur, 1978), and are related to
the geomorphic units (see appendix 2).
Table 1: Spatial extent of remnant vegetation in the Brockman River catchment.
Total area (km
2
)
1,520
Number of remnants
2,000
Total area of remnant vegetation (km
2
)
770
% Total remnant area
51%
Remnant vegetation reserved (km
2
)
201
% Original area reserved
13
% Remnant area reserved
26
Source: Connell and Ebert (2001).
2.4
Water and Rivers Commission
Natural Resource Management Plan for the Brockman River Catchment
Table 2: Landuse of remnant vegetation in the Brockman River catchment.
Tenure
Number
Area km
2
(% of remnant area in brackets)
Study area
NA
1521
Conservation and Natural Landuse
517*
629 (82%)
Other Landuse
5481*
141 (18%)
CALM Reserved**
31*
201 (13%)
TOTAL
1521
770 (51%)
* the comparatively large number of remnants is due to the road/cadastre/landuse intersections process detailed in the
methodology.
Table 3: Size class of native vegetation remnants by landuse.
Remnant size (ha)
Conservation and
Other Landuse
CALM Reserved*
Total**
Natural Landuse
Number Area
(km
2
)
Number Area
(km
2
)
Number Area
(km
2
) Number Area
(km
2
)
< 1 ha
324
0.67
3667
9.94
1
0.0
3991
10.61
0 to 10
82
2.77
1542
45.48
1
0.0
1624
48.25
10 to 50
43
10.27
231
48.31
4
0.6
274
58.58
50 to 100
16
11.87
31
21.77
7
2.2
47
33.64
100 to 500
34
67.09
10
15.36
2
1.4
44
82.45
> 500
18
536.49
0
0
16
197.0
18
536.49
TOTAL
517
629.18
5481
140.86
31
201.2
5998
770
Note: Remnant area calculations are based on a remnant vegetation – landuse GIS intersection; hence their numbers
may not match Remnant counts in some other tables.
* CALM Reserved land is a subset of the Conservation and Natural Landuse category.
** Total Number and Total Area are calculated as the sums of the first two landuse categories.
2.5
Water and Rivers Commission
Natural Resource Management Plan for the Brockman River Catchment
Table 4: Spatial extent of vegetation complexes pre- and post-clearing and currently reserved.
Vegetation complex
Pre-clearing
Post-clearing
Reserved
Retained
Reserved
No.
Area (ha)
No.
Area (ha)
No.
Area (ha)
(%)
(%)
Bindoon Complex
3
8900
258
2441
6
191
27.4
2.1**
Cook Complex
14
542
22
416
0
0
76.7
0.0**
Coolakin Complex in
low rainfall
29
20560
582
9085
20
3270
44.2
15.9
Cullula Complex
1
18977
205
10411
2
826
54.9
4.4**
Darling Scarp Complex
4
80
8
33
0
0
41.7
0.0**
Dwellingup & Yalanbee
Complex, low - medium
rainfall
2
1164
9
1073
4
688
92.2
59.1
Dwellingup,Yalanbee &
Hester Complex, low -
medium rainfall
5
1535
8
1532
8
1398
99.8
91.1
Helena Complex, low -
medium rainfall
1
4358
71
2127
4
90
48.8
2.1**
Karamal Complex-South
1
5805
36
4180
2
2704
72.0
46.6
Michibin Complex
5
19342
407
7940
6
1353
41.1
7.0**
Mogumber Complex-
North
2
2225
8
1428
0
0
64.2
0.0**
Mogumber Complex-
South
8
3546
111
1383
0
0
39.0
0.0**
Murray & Bindoon
Complex, low - medium
rainfall
3
12456
299
5424
14
603
43.6
4.8**
Nooning Complex
1
2698
141
553
2
170
20.5
6.3**
Pindalup & Yarragil
Complex, low - medium
rainfall
11
4934
76
3514
11
1648
71.2
33.4
Reagan Complex#
1
3
3
0.6
0
0
17.6*
0.0
Wannamal Complex
6
2775
85
888
6
41
32.0
1.5**
Williams-Avon-
Brockman-Mumballup
Complex
1
959
82
136
1
2
14.2*
0.2**
Yalanbee & Dwellingup
Complex, low rainfall
3
16922
153
13714
14
5098
81.0
30.1
Yalanbee Complex in
low rainfall
50
24316
804
10730
15
2190
44.1
9.0**
TOTAL
151
152104
3368
77017
115
20272
50.6
13.3
NOTES
# vegetation complex found at the periphery of the catchment
* less than 20% of original area remains
** less than 10% of original area reserved
2.6
Water and Rivers Commission
Natural Resource Management Plan for the Brockman River Catchment
Figure 4: Condition of Remnant Native Vegetation.
2.7
Water and Rivers Commission
Natural Resource Management Plan for the Brockman River Catchment
Figure 5: Landuse of remnant vegetation in the Brockman River catchment.
10
2.8
Water and Rivers Commission
Natural Resource Management Plan for the Brockman River Catchment
Figure 6: System 6 vegetation complexes in the Brockman River catchment pre-settlement.
2.9
Water and Rivers Commission
Natural Resource Management Plan for the Brockman River Catchment
Figure 7: Remnant vegetation complexes in the Brockman River catchment.
2.10
Water and Rivers Commission
Natural Resource Management Plan for the Brockman River Catchment
2.1.5 Native plants and animals
In the Brockman River catchment, continued destruction
and fragmentation of habitat through clearing, grazing,
land degradation, declining water quality, introduction
of exotic species, disease and changes to fire regimes has
contributed to declining native plant and animal
populations. This decline has caused loss of native
species and will lead to other species becoming
vulnerable.
However, some animals have adapted well to the
changed landscape and their numbers continue to
increase. These include western grey kangaroos
(Macropus fuliginosus), galahs (Cactua roseicapilla),
ravens (Corvus coronoides), magpies (Gymnorhina
dorsalis), corellas ( Cacatua tenuirostris) and the Port
Lincoln parrot (Barnardius zonarius) and their numbers
continue to increase.
Rare and priority flora
There are 8 species of Declared Rare Flora and 50
Priority Flora within the catchment boundary. Most of
these are found on the roadside verges, others are found
growing on private property and some are within
reserves. This makes them particularly vulnerable to
extinction. Included in the rare flora is Grass Wattle
(Acacia anomala) and Star Sun Orchid (Thelmytra
stellata) (see plate 1) to the south, and to the north,
Bindoon Star Bush (Asterolasia nivea), Darwinea
acerosa and Spirogardnera rubescens while Eleocharis
keigheryi is found near watercourses and wetlands. A list
of all plants recorded in the Shire of Chittering are listed
in appendix 3, included is a list of the rare and priority
flora.
Rare and priority fauna
The Western Shield program was initiated by CALM to
increase introduced predator control, captive breeding
programs and reintroduction of native animals to their
former habitat. Fox control using “1080” poison and
fauna re-introductions, have been ongoing in Julimar
State Forest since 1993. Native species reintroduced are
chuditch (Dasyurus geoffroyii), quenda (Isooden
obesulus fusciventor), woylies ( Bettongia penicilliata),
tammar wallaby (Macropus eugenii) and brush-tailed
possum (Trichosurus vulpecula). These native animals
are still vulnerable and in need of protection.
The critically endangered western swamp tortoise
(Pseudemydura umbrina) (see plate 2) has also been
released in the north of the catchment at Mogumber.
Winter wet clay depressions in the area provide suitable
habitat in which twenty tortoises were released in an
attempt to establish a wild population. Fox control in the
reserves and on surrounding properties is vital for their
survival and the population is closely monitored by
CALM (table 5).
Birds
Loss of native vegetation on which most land birds in the
southwest of Western Australia (83%) depend for all or
part of their annual requirements (Smith 1987) will
inevitably result in significant changes to populations
and possible species loss.
Populations of species such as the Carnaby’s cockatoo
(Calyptorhynchus funereus latirostris) have been much
reduced through habitat loss (Saunders and Ingram,
1987).
Bird species recorded in the Julimar State Forest that are
at or near the northern limit of their distributions include
the rufous tree creeper (Climacteris rufa) and the
splendid fairy wren (Malaurus splendens).
Bush birds found within the catchment are typical of the
jarrah-marri woodland and the wandoo woodland
habitats (Department of Defence, 1998).
One hundred and twenty nine species of bird have been
recorded from the Wannamal area (Buchanan, 1997)
including the Carnaby’s Black Cockatoo
(Calyptorhynchus latirostris). Wannamal birds have
been studied on behalf of CALM and other authorities
for some years. The first report included Lake Wannamal
and surveys have been kept up for both water birds and
bush birds since, though not continuously.
The Wannamal Lake system forms the headwaters of the
Brockman River and is a major breeding and drought
refuge area for waterbirds. Fifty-two species of water
birds have been recorded in the system, seven listed
under treaties. Freckled duck (Stictonetta naevosa)
occurs regularly in the system. The Mogumber Swamp
is one of the few wetlands in south-western Australia in
which Australian crake (Porzana fluminea) is known to
breed regularly in low sedges mixed with low shrubs.
Other species for which the Wannamal Lake is
regionally significant are Australasian grebe
2.11
Water and Rivers Commission
Natural Resource Management Plan for the Brockman River Catchment
(Tachybaptus novaehollandiae), hardhead (Aytha
australis) and black-tailed native-hen ( Gallinula
ventralis). Wannamal Lake is included on the Register of
the National Estate (Environment Australia, 2001).
The Chittering-Needoonga Lakes are part of the
Brockman River and are a major breeding area for water
birds. Forty-two species have been recorded, four listed
under treaties. The Lakes are a major breeding place for
the great egret (Egretta alba) and the rufous night heron
(Nycticorax caledonicus) in Western Australia. Freckled
duck (Stictonetta naevosa) occurs regularly with
vegetation and the spring water levels in the lakes
making the site suitable for breeding.
Other breeding colonies in Lake Needoonga include the
Australian white ibis (Threskiornis molucca), yellow-
billed spoonbill (Platalea flavipes) and little pied
cormorant (Phalacrocorax melanoleucos). The site is
regionally significant for Australasian grebe
(Tachybaptus novaehollandiae), great egret (Egretta
and alba), yellow-billed spoonbill (Platealea flavipes),
maned duck (Chenonetta jubata) (Environment
Australia, 2001).
Both of these wetland systems are under threat from
increasing salinity, siltation and eutrophication. The
Wannamal wetland system is also under threat from
excessive inundation causing the death of wetland trees.
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