Natural resource management plan for the brockman river



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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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