SHIRES OF BEVERLEY AND BROOKTON
DISTRICT RURAL STRATEGY
PART II
PHYSICAL CHARACTERISTIC STUDY
Prepared by : Land Assessment Pty Ltd
1998
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PART II - PHYSICAL CHARACTERISTICS STUDY
2.1
INTRODUCTION
This part of the report and its associated mapping has been prepared by Land Assessment Pty Ltd to assist the
preparation of a District Rural Strategy for the adjacent Shire of Beverley and Brookton within the "Wheat Belt" of
Western Australia. As indicated previously, the total study area covers approximately 393,600 ha within the Avon
River Catchment, and is centred approximately 135 km east of Perth (Map 1).
Rural land within both Shires is subject to pressure for subdivision, primarily to cater for demand for
rural-residential or hobby farming blocks. However there is also subdivisional pressure associated with
diversification of broad-acre farming into activities such as agroforestry, aquaculture, horticulture and tourism
related ventures.
The two Shires are generally similar in relation to broad land types and the planning and environmental issues
they must address. In recognition of these similarities, and in order to comprehensively plan and manage the
future development of their rural areas, the two Councils have undertaken to prepare a combined 'District' Rural
Strategy in accordance with guidelines provided by the Western Australian Planning Commission.
This part of the District Rural Strategy Report is the essential first component of the District Rural Strategy. It
documents the "Physical Characteristics" of the area covering both Beverley and Brookton Shires, and outlines
the relevant implications for land use planning and management. This work is based on a collation and review of
data from various Government agencies, and brief field reconnaissance trips.
Not forsaking the planning value of the land resources inventory provided herein, it is important to emphasise that
more detailed field work and capability assessment will need to be undertaken in relation to specific subdivision
and development proposals. Such investigations would be the responsibility of the proponent, and should aim to
refine the level of detail presented in the Strategy in terms of the characteristics and capability of the subject land
to support the proposed change in land use.
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MAP 1
LOCATION OF STUDY AREA
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2.2
NATURAL RESOURCES
A regional perspective of the natural resources of the Shires of Beverley Mid Brookton is provided here, primarily
by reference to the following published and unpublished material.
•
Land Resources of the Northam Region (Lantzke and Fulton 1993): Department of Agriculture
Western Australia Land Resources Series No 11.
•
Corrigin Land Resources Survey (Verboom and Galloway, in preparation). Produced by the
Natural Resources Assessment Group, Agriculture WA.
•
Native Vegetation Handbooks for the Shires of Beverley and Brookton (Safstrom, in
preparation). Produced by the Division of Regional Operations, Agriculture WA.
•
The Vegetation of the Corrigin Area, Western Australia. Map and Explanatory Memoir, 1:250
000 series (Beard, 1980). Vegetation Survey of Western Australia.
•
The Vegetation of the Pinjarra Area, Western Australia. Map and Explanatory Memoir, 1:250
000 series (Beard, 1979). Vegetation Survey of Western Australia.
•
Corrigin Western Australia 1:250 000 Geological Series Explanatory Notes. Sheet SI 50-3
(Chin, 1986). Geological Survey of Western Australia.
•
Pinjarra Western Australia 1:250 000 Geological Series Explanatory Notes. Sheet SI 50-2
(Wilde and Low, 1980). Geological Survey of Western Australia.
The sections 2.2.1 - 2.2.6 summarise relevant material from those reports in order to provide a framework for the
determination of policies and policy areas within the District Rural Strategy. In the case of the unpublished
reference material, considerable assistance has been provided by the authors through access to the draft reports
and data. This is gratefully acknowledged as it has enabled the District Rural Strategy to be based upon the most
up-to-date natural resource information.
2.2.1
Climate
The study area experiences a Mediterranean climate, characterised by cool, wet winters and hot, dry summers.
On average, the annual rainfall is 420 mm at Beverley and 466 mm at Brookton. However rainfall distribution
varies markedly from west to east. In the western portion of Beverley, occupied by State Forest, the annual
rainfall is about 900 mm, while in the eastern most portion of Brookton it is less than 400. Most of the rain falls
during the cool winter months of May to August, and is associated with the passage of winter cold fronts.
Thunderstorms may locally provide rain during the summer.
Average maximum temperatures range from about 33 °C in January to 16 °C in July with minimum temperatures
of around 16 °C in February to 4 or 5 °C in August. In the Avon Valley dense air falls to the valley floor resulting in
temperature inversions during winter months, which are responsible for winter fogs. Frosts occur from May to
September, and are most frequent in July and August.
Windy conditions are experienced in the Shires from late winter through spring and summer. The prevailing winds
in July and August are from the west, north west and north, while summer winds veer from south - west through
south and east.
2.2.2
Geology Landforms and Soils
2.2.2.1 Geology
The Shires of Beverley and Brookton are underlain by Archaean rocks of the Yilgarn Block which has
been a relatively stable part of the earth's crust for 2400 million years. The Great Plateau of Western
Australia, referred to locally as the Darling Plateau, is the surface expression of the Yilgarn Block. The
ancient 'basement' rocks of the Darling Plateau are composed of predominantly granite and
metamorphics with localised intrusions of narrow quartz or dolerite dykes.
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The surface of the Darling Plateau was once extensively mantled by Tertiary (Cainozoic) laterite and
associated weathering products. Although the plateau is now substantially dissected by major drainage
systems, remnants of the lateritised surface occur in upper parts of the landscape and along drainage
divides. In upland areas to the west, these remnants consist of ironstone gravels and extensive sheets
of lateritic duricrust. Further to the east, the remnants occur as sandplain deposits. Throughout all lower
parts of the landscape there are geologically more recent alluvium and colluvium deposits of Quaternary
age.
An important geological feature within the study area is the Jimperding Metamorphic Complex which
extends from north of Toodyay to the east of Beverley. This zone within the Archaean basement rocks,
is about 40 km wide and its alignment coincides with that of the Avon Valley. This is thought to be due to
its composition of predominantly gneissic rocks which are more easily weathered than granites which
are dominant elsewhere.
2.2.2.2 Processes affecting Landform and Soil Development
Approximately 60 to 100 million years ago, during the Tertiary period, this portion of Western Australia
had a more temperate to tropical climate which led to high rates of rock weathering and soil formation.
The deep soils that formed were characterised by accumulations of iron, aluminium and quartz in the
upper parts of the profile, and intense leaching of other constituents from the remainder of the profile.
These 'lateritic' profiles were sometimes tens of metres deep and consisted of a number of distinct
zones as shown in Figure 1.
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The upper portions of the lateritic profile consist of sands and gravels with boulders or pavements of
ferruginous duricrust or ironstone. Underlying these surface materials, which may be as much as 5 m
deep, there is a mottled zone of sandy kaolinitic clays with iron staining. Beneath the mottled zone is a
deep pallid zone of kaolinitic clay and residual quartz. Within the pallid zone chemical weathering has
led to the depletion of most elements essential to plant growth. and has also led to the accumulation of
soluble salts.
During the Pleistocene period, from 2 million years until about 10 000 years ago, geological uplift of the
south-west of Western Australia occurred. This resulted in development of the major drainage systems
and initiated a cycle of erosion which stripped the lateritic mantle of the Darling Plateau to varying
degrees exposing the lateritic profile and, in places, the bedrock below.
The extent of dissection of this lateritic profile can be used to explain the development of soils
throughout much of the south-west of Western Australia. Where little or no erosion of the lateritic profile
has occurred, these fossil soils have been preserved within a flat to gently undulating upland landscape
either as sandplain or as 'buckshot gravels' above 'breakaway' slopes.
Where some dissection of the lateritic profile has occurred, the terrain is more sloping with a complex of
geomorphic elements consisting of valley side spurs capped with ironstone gravel, and pediments below
the breakaways with exposed pallid zones of truncated laterites. Duplex, loamy sand or sandy loam
over clay, soils have developed here.
Where removal of the lateritic profile has been complete, fresh exposures of the underlying bedrock
occur, giving rise to predominantly yellow gritty duplex soils over granite and gneiss, and red loamy soils
on dolerite. Large, smooth, steep sided dome shaped hills of homogeneous granitic rock occur,
particularly in the western portion of the Shire of Beverley.
Broad aprons of colluvium, also form the parent material for many soils within the study area. These
aprons lead down to valley floors where other soils are developed from water lain sediments.
The rejuvenation of drainage following uplift of the south-western portion of Western Australia is also a
factor controlling the form and shape of the major valley systems.
Upstream within the Avon catchment, valleys are broad and shallow, with low gradients and braided and
meandering stream channels. Drainage is sluggish and, inland of the Meckering line, there are
extensive salt lakes with marginal lunette dunes. Old, deeply weathered soils are widespread in this
landscape.
Downstream, stages of progressively increasing sharpness and depth of incision of valleys are
observable with more clearly defined river channels. In these western portions of the study area, the
valley sides are steeper and carry younger and fresher soil materials. The older deeply weathered soils
are less extensive, occurring only along drainage divides in the upland portions of the landscape.
2.2.2.3 Physiographic Regions
Progressing inland from west to east, the Shires encompass four broad physiographic regions. These
are:
-
The Darling Range Zone
-
The West Kokeby Zone
-
The Zone of Rejuvenated Drainage
-
The Zone of Ancient Drainage
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Although boundaries between these zones are relatively broad and gradational, each zone has a
characteristic suite of landforms, soils and vegetation relating to the degree of dissection of the original
lateritic surface.
The Darling Range Zone:
•
This zone occurs in the western portion of both Shires. The landscape consists of an undulating
lateritic plateau with narrow, swampy, minor valley floors. The plateau uplands contain ironstone
'buckshot' gravels soils while the dissected lateritic slopes have Predominantly gravelly duplex soils,
In the east of this zone, eastward flowing streams and rivers such as Talbot Brook and the Dale
River have cut back into this plateau creating steep, gravelly (lateritic) and rocky valleys.
The West Kokeby Zone:
•
This occurs as a relatively small area nested between the Darling Range Zone and the Zone of
Rejuvenated Drainage. Dissection of the lateritic profile here has left a low-lying, flat, sandy
landscape with gently undulating sideslopes and a number of swamps on valley floors. The soils
are predominantly deep sandy surfaced duplex types or deep sands.
The Zone of Rejuvenated Drainage:
•
This zone is defined by the Meckering Line to the east and the Darling Range Zone to
the west. It encompasses the major portion of the Shire of Beverley and about a third of the Shire of
Brookton. It represents the 'inner wheatbelt' and the central portion of the Avon Valley.
•
The Zone of Rejuvenated Drainage is characterised by a greater degree of dissection
of the landscape than in the Zone of Ancient Drainage to the east. Thus steeper, narrower valleys
are formed which contain rivers and creeks that flow every winter. Large areas of yellow duplex
soils have formed here from the dissection of the lateritic profile. In areas where the lateritic profile
has been completely removed there are extensive areas of rocky, red and greyish soils developed
from fresh rock. The valley floors contain alluvial clays, loams and sands.
The Zone of Ancient Drainage:
•
This zone includes all land east of the limit of geological rejuvenation (Meckering Line)
and extends beyond the eastern edge of the wheatbelt. It represents the 'outer wheatbelt' and the
eastern inland portion of the Avon Valley.
•
The landscape consists of a gently undulating plateau, with wide convex divides, long
gentle slopes and broad valleys that contain salt lakes at their lowest point. The chains of salt lakes
are sediment filled remnants of an ancient drainage system that now flows only in wet years.
•
In the upland portions of the landscape there are large areas of yellow sandplain and
gravelly soils. Dissection of the lateritic profile on the gently sloping hillsides has resulted in the
formation of hardsetting grey duplex soils with some sandy surfaced duplex soils do the lower
slopes. The valley floors contain either heavy red and grey soils, or pale sandy surfaced duplex
soils.
2.2.2.4 Soil Landscapes
The four physiographic zones, in combination with the degree of dissection of the original lateritic profile,
form the framework for 'soil landscapes' mapping over the Shires of Beverley and Brookton. The
physiographic zones, with soil landscape units characteristic of the Beverley Shire are shown in Figures
2 - 4. Table 1 groups the soil landscape systems according to degree of landscape dissection, as well
as their occurrence within physiographic zones. It provides a legend to the soil landscapes mapping
shown in Maps 2 and 3.
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Three sources land resource data have been used to compile the soil landscape mapping. The most
detailed, at an original publication scale of 1:100 000, and covering the major part of the Shire of
Beverley, is from the 'Land Resources of the Northam Region' (Lantzke and Fulton; Agriculture WA
1993). To the south, over most of the Shire of Brookton, preliminary broader scale mapping of the
Corrigin area by Verboom and Galloway (Agriculture WA undated) is presented here. A relatively small
portion of the western part of both Shires is also covered by 1: 250 000 scale mapping of the Darling
System (Churchward and McArthur CSIRO 1980).
Details of the soil landscapes are presented within the Appendices as follows;
Appendix
A
Description of soil landscape systems.
B
List of soils for Beverley - Brookton area.
C
Correlation of Corrigin survey soils (WA Soils Groups) with Northam survey soil
types.
D
Land quality values for soil type/groups.
For more detailed descriptions of the soils and their land use attributes, the reader is referred to
Agriculture WA. In particular, reference should be made to the soils publication for each Physiographic
Zone within the Northam Region (Fulton and Lantzke, 1993; Lantzke 1992; Lantzke 1993) since nearly
all soils within the unpublished Corrigin Survey (covering most of Brookton) can be correlated to soils
described in those publications. The correlations enable assessments of land capability, agricultural
quality and land degradation hazards to be made over the entire study area.
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Figure 2
Idealised block diagram showing the soil landscape units of the Darling Range and
West Kokeby Zones
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Figure 3
Idealised block diagram showing the soil landscape units that occur in the zone of
rejuvenated drainage
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Figure 4
Idealised block diagram showing the soil landscape units that occur in the zone of
ancient drainage
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TABLE 1.
SOIL - LANDSCAPE SYSTEMS* OF THE BEVERLEY - BROOKTON AREA
Gcomorphic Grouping
(Reflecting dissection of
lateritic profile)
Uplands with lateritic profile
remnants and including
minor valleys.
Darling Range Zone
West Kokeby Zone
Northam Survey Area
Pindalup (Pn) Yalanbee
(Ya)
System 6 Survey Area
Coolakin (Ck),
Pindalup (Pn) Yalanbee
(Y) Goonaping (G)
Corrigin Survey Area
Wundowie (Wn)
Directed lateritic terrain or
Northam Survey Area Northam Survey Area
hilly terrain with lateritic
Kokeby (K) Sheahan
Leaver(L)
profile remnants (sands or
(S)
gravels)
Corrigin Survey Area
West Kokeby (Wk>
Undulating to hilly terrain
Northam Survey Area
with freshly exposed hedrock Michibin (Mn) Steep
Rock)' Hills (R)
System 6 Survey Area
Michibin (Mn)
Corrigin Survey Area
Clacklinc (Cc)
TABLE I.
Zone of Rejuvenated
Drainage
Zone of Ancient
Drainage
Northam Survey Area
Quailing (Qu)
Northam Survey Area
Ulva(U)
Corrigin Survey Area
Bendering (Bd)
Corrigin (Cg) Kunjin
(Kj) Yclbeni (Ye)
Northam Survey Area
Ewerts (Es 1)
Corrigin Survey Area
Walyuring (Wy)
Northam Survey Area
Booraan (B)
Corrigin Survey Area
Walyuring (Wy) Kulin
(Kn) BilgeringTBi)
Northam Survey Area
Danberrin (D)
Corrigin Survey Area
Danberrin (Db)
Jelcobine (Jc) - minor
Northam Survey Area
York(Yl, Y2)
Hamersley (H) Steep
Rocky Hills (R)
Corrigin Survey Area
Greenhills (Gh)
Jelcobine (Jc)
Cunyeenying (Cn)
Boyagin {Bn)
SOIL - LANDSCAPE SYSTEMS" OF THE BEVERLEY - BROOKTON AREA (continued)
Geomorphic Grouping
(Reflecting dissection of
lateritic profile)
Major valley floors
Darling Range Zone
W,est Kokcbj Zone
Zone of Rejuvenated
Drainage
Northam Survey Area
Williams (W)
Corrigin Survey Area
Wickepin (Wp)
System 6 Survey Area
Williams (W)
Northam Survey Area
Dale (Da) Maitland
(Ma)
Northam Survey Area
Mortlock (Mo)
Avon(A)
Corrigin Survey Area
Wickepin (Wp)
* Refer to Appendix A for description of mapping units and listing of component soils
Zone of Ancient
Drainage
Northam Survev Area
Bclka (Be) Mcrredin
(M) Baandcc (Ba)
Corrigin Survey Area
Wickepin <Wp)
Alderside <As) Jilakin
(Jk)
ANCIENT DRAINAGE
ZONE OF REJUVENATED DRAINAGI
ZONE OF REJUVENATED DRAINAGE
GEOMORPHC GROUPINGS
DARUNC RANGE ZONE
A
Upland areas with lateritic profile remnants (gravel plain or sand plain)
Hillslopes ■ dissected lateritic terrain
Hillslopes ■ with fresh bedrock exposure
valleyf cors
SOURCE: Agriculture W.A. ■ Natural Resource Assessment Croup various sources
Interpretation by Land Assessment Pty Ltd NOTE: Soli
landscape symbols can chanoe acres survey boundaries
BEVERLEY / BROOKTON RURAL
STRATEGY SHIRE
OF BROOKTON
SOIL LANDSCAPE SYSTEMS
MAP 3
EC BJTPS / rracn? CM
2.2.2.5 Land Capability
Land capability is a term used to express the ability of land to support a proposed form of land use with
minimal risk of degradation to its soil and water resources. To progress towards sustainable rural land
use, planning decisions need to be based on an understanding of the nature of land and its capability.
The general methodology for land capability assessment involves comparing the physical requirements
of proposed land uses with the existing qualities of the subject land. Land qualities include such things
as 'erosion risk', 'soil workability' (ease of cultivation), 'plant rooting conditions' and the soil's 'nutrient
retention ability'.
Appendix D provides land quality values for each of the major soils occurring within the soil landscape
systems. This information has been gleaned largely from the soils publications associated with the
Northam region survey (Lantzke and Fulton 1993) and provides the basis for the broad evaluations of
land use capability presented in Appendix E.
From this information two key interpretations can be made. These are;
•
areas most at risk from land degradation, and
•
relative 'agricultural quality' of land.
2.2.2.6 Areas at Risk from Land Degradation
If inadequately managed, rural land within both Shires is susceptible to various forms of land
degradation. Land degradation is accompanied by reduced agricultural productivity and a loss of
conservation values.
Within the Shires of Beverley and Brookton the most prevalent land degradation problems are salinity
and waterlogging, water and wind erosion, and soil acidification. Soil landscape systems considered
particularly susceptible to various forms of degradation are shown in Table 2.
Salinity
It is generally accepted that the principal cause of salinity in much of the wheatbelt has been the
extensive removal of native, deep rooted, perennial vegetation and its replacement with annual, shallow
rooted, crops and pastures. The introduced crops and pastures use much less water than the native
vegetation. Thus with clearing, water tables rise, and mobilise soluble salts normally stored deep in the
unsaturated zone of the soil.
Salinity of the soils and groundwater has always been a problem in the lower rainfall valleys in the
eastern areas, and with clearing has become increasingly important elsewhere.
Within the broad flat eastern valleys of both Shires there are areas, of what were previously productive
agricultural soils, now rendered largely unsuitable for agriculture due to high salt concentrations and
waterlogging. This is because extensive weathering of the landscape has brought the salt storage
zones within the lateritic profile closer to the surface, and because there is little leaching and less
effective surface drainage, in this low rainfall area.
In the central portions of both Shires, where there are extensive areas of relatively shallow soils over
bedrock, the deep weathering zones of the laterite profile which contain the high salt storage are largely
absent. Consequently the development of secondary salinity is of lesser extent, and the main problem is
due to salt, which was developed elsewhere, being transported through the system.
In the western portions of the Shires, the lateritic profile is relatively intact with the salt storage zones at
depths which are exposed only in the more incised drainage lines and river valleys. Furthermore there is
a greater percentage of vegetation cover, mainly due to reserves and State Forest, and rainfall is
higher. As a result salinity is less prevalent than in areas to the east.
The Shire of Beverley had 4313 ha (2.85 % of arable land ) in 1989 affected by severe salinity, while in
the Shire of Brookton there was 6631 ha or 5.53% of arable land affected (George, 1990).
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Areas considered particularly susceptible to salinity are based primarily on interpretations from the
Northam Region Land Resources study (Lantzke and Fulton 1993). These are the soil landscape
systems (Figures 6 and 7) with greater than 50 % occurrence of soils with a moderately high or worse
risk of salinity. They include the low-lying broad valley floors and associated salt lakes of Baandee and
Belka (saline) systems, as well as the narrow drainage lines of Hamersley system within the Avon
Valley hillslopes. Draft interpretations from the Corrigin survey area (Verboom and Galloway in prep)
also indicate that similar valley floor terrain within the Jilakin, Alderside, Mortlock, and parts of Wickepin
systems, are also susceptible
To a lesser extent, there are salt susceptible areas along drainage lines with the Ewerts system, in
seepage areas within parts of York system, and on parts of the valley floors within Williams system
(Safstrom in prep). Individual soils which are particularly susceptible to salinity can be determined by
reference to Appendix D
Waterlogging
Waterlogging is sometimes, but not always, associated with salinity. Waterlogging is most prevalent in
areas with greater than 400 mm annual rainfall and particularly on duplex and clay soils in plains and
valley floors. Severely waterlogging occurs in the salt lakes of the Baandee soil landscape system, the
thin midslope drainage lines of the Hamersley system, and the swampy Pindalup valleys which occur in
the far western portions of both Shires. The flatter portions of valley floors of the Mortlock, Maitland,
Williams, Dale, Alderside and Wickepin systems are also susceptible to waterlogging. Individual soils
which are particularly susceptible can be determined by reference to the land quality table in Appendix
D.
Wind Erosion
Loose sandy surfaced soils are susceptible to wind erosion if surface vegetative cover is depleted,
particularly following cultivation and overgrazing. Areas of sandplain soils which are particularly
susceptible to wind erosion occur within the Ulva, Quailing, Kokeby and Sheahan systems, and to a
lesser extent, within the Ewerts system. (Lantzke and Fulton 1993). Draft interpretations from the
Corrigin survey area (Verboom and Galloway in prep) also indicate that soils within the Clackline,
Jelcobine and West Kokeby systems are susceptible to wind erosion.
Although largely determined by land management and climatic factors, individual soils at risk from wind
erosion can be determined by reference to the land quality table in Appendix D.
Water Erosion
The incidence of water erosion is greatly dependent on the slope of the land and land management
practices. Erosion is commonly associated with the limited areas of breakaways and associated highly
erodible soils within the Leaver system, which forms part of the dissected lateritic terrain in the western
portion of the study area. Steeper slopes within the parts of the York system are also particularly
susceptible to water erosion. (Lantzke and Fulton 1993). Draft interpretations from the Corrigin survey
area (Verboom and Galloway in prep) indicate that soils downslope from areas of bare rock in the
Boyagin system are also susceptible.
Although largely determined by topography, land management and climatic factors, individual soils at
risk from water erosion can be determined by reference to the land quality table in Appendix D.
Soil acidification
Soils in the agricultural zone of Western Australia are becoming more acid as a result of farming
practices, including the use of ammonium based fertilisers and clover pastures. Acidification can inhibit
the growth of plant roots and render soils more susceptible to degradation by wind and water erosion.
With the exception of the Avon River floodplain and the swampy Pindalup valleys in the far west of the
study area, all land west of the Meckering Line (outside the Zone of Ancient Drainage) has a high risk of
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surface soil acidification. In addition, the more freely draining soil types are also at risk of subsoil
acidification.
2.2.2.7 Relative Quality of Agricultural Land
In 1994 Cabinet adopted the following position statement:
"The Western Australian Government considers that productive agricultural land is a finite National and
State resource that must be conserved and managed 'for the longer term. As a general objective, the
exercise of planning powers should be used to protect such land from those developments, activities or
influences that lead to its alienation or diminished productivity, while always accepting the need for land
for urban areas and other uses of State significance".
A broad assessment of the relative agricultural quality of different areas within the Shires is therefore
important in relation to the objective of protecting productive agricultural land. It is also important in
relation to seeking opportunities for agricultural diversification, and in identifying areas suitable for small
holdings.
Table 3 and Maps 4 and 5 show, in broad terms, the relative 'agricultural quality' of land within the two
Shires for the main farming activities; grazing and cereal cropping. For each soil landscape system,
agricultural quality has been assessed from a consideration of land evaluation results (Appendix E) as
well as the susceptibility of particular areas to land degradation.
The land evaluation results in Appendix E provide, for individual soils, a qualitative ranking of land
capability for grazing, cereal cropping and horticulture. The capability assessments for grazing and
cereal cropping are derived either directly from the "Land Resources of the Northam Region" report
(Lantzke and Fulton 1993) or, for other soils in the Brookton area, by soil correlation. The capability
assessment for general horticulture, which includes' tree crops, is based on earlier work by Land
Assessment Pty Ltd (1996). Soil capability ratings for all land uses are independent of landform and
water supply factors. The capability ratings for the component soil types have been combined in a
manner to provide an overall assessment of agricultural quality for each soil landscape system.
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TABLE 3
TABLE 3.
RELATIVE AGRICULTURAL QUALITY OF LAND
RELATIVE AGRICULTURAL QUALITY OF LAND
Agricultural Soil Landscape Systems
Quality
Northam and
Corrigin Survey
System 6 Survey Area
Areas
Avon (A) Belka
Bendering (Bd)
High
(Be) Booraan (B) Greenhills (Gh)
Ewerts (Es) Leaver
(L) Merredin (M)
Michibin (Mn)
York (Y)
Moderate
Low
Very low
Description
Xreas where the majority
of soils have a fair to high
capability for both grazing
and cropping. Land
degradation hazards are
minor or affect only small
portions.
Hamersley (H)
Bilgering (Bi)
Areas where the majority
Mortlock (Mo)
Clackline (Cc)
of soils have a fair to high
Quailing (Qu) Ulva Corrigin Cg)
capability for grazing but a
(U) Williams (W) Danberrin (Db)
lesser percentage are suited
Yalanbee (Ya)
Jelcobine (Jc)
to cropping. Land
Kulin (Kn) Kunjin degradation hazards,
(Kj) Mortlock (Mo) although more significant,
Nukering (Nk)
are still generally
Walyuring (Wy)
manageable within current
Wickepin (Wp)
farming systems.
Wundowie (Wn)
Yelbeni (Ye)
Dale (Da) Kokeby Alderside (As)
Areas with sites generally
(K) Pindalup (Pn) Boyagin (Bn)
capable of supporting
Steep Rocky Hills Cunyeenying (Cn) grazing but not cropping,
(R) Coolakin (Ck) West Kokeby (Wk) and subject to land
Goonaping (G)
degradation hazards which
require careful management
practices.
Baandee (Ba)
Areas generally unsuitable
Belka saline (Be s)
for agricultural use due to
Maitland (Ma)
high risk of land
Sheahan (S)
degradation or very low
productivity.
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MAP 4
RELATIVE AGRICULTURAL QUALITY - SHIRE OF BEVERLEY
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2.2.3
Mineral Resources and Extractive Materials
The economic geology of the region mainly concerns the extraction of construction materials; especially kaolin for
bricks and gravel for roads. Numerous occurrences of metallic minerals are reported but none are particularly
prospective. These are;
•
A semi ball clay, thought to be of sedimentary origin, occurs near Brookton.
•
A kaolin prospect occurs 26 km north east of Brookton on the south east side of Yenyening
lakes.
•
Clear colourless to pale smoky brown quartz gemstones have been found in 1952 10 km east
of Beverley.
•
Gypsum occurs in most lake sediments but is rarely pure enough or of sufficient volume to
attract economic interest.
•
Wolfram and tin were reported in 1908 from the Avon Valley about 20 km east of Brookton
Concentrations of wolfram are low and the reputed tin mineralisation has not been substantiated.
•
Uranium minerals were discovered in 1954 in quartz in the vicinity of the wolfram occurrence
20 km east of Brookton.
2.2.4
Vegetation
2.2.4.1 Original Communities
The original vegetation of the region has been mapped and described by Beard (1979, 1980). The major
parts of the Shires of Beverley and Brookton fall into the Avon Botanical District, although a small area
along the western boundary of both Shires is part of the Darling District (Dale Subdistrict). In each of the
Shires, there are a number of different vegetation types whose occurrence is strongly influenced by
climatic and soil conditions. These are described briefly below. For further details the reader is referred
to Beards work and to the 'Native Vegetation Handbooks' produced for the each Shire by Agriculture
WA.
Jarrah and Marri Forest
The jarrah forest occurs in the higher rainfall western areas on the lateritic plateau (Darling District) and
screes descending its edges. Jarrah (Eucalyptus marginata) is the dominant tree, and is normally
accompanied by marri (E. calophylla). On some sites it will also be associated with blackbutt (E. patens),
wandoo (E. wandoo) and powderbark wandoo (E. accedens). There is also often a lower layer of small
trees, including Banksia grandis, Casuarina fraserana and Persoonia longifolia.
Jarrah - Marri - Wandoo - Powderbark - Brown Mallet Woodlands
On the eastern edge of the lateritic plateau (Darling grading into Avon District), woodland replaces the
jarrah forest, due to the declining rainfall. The principal components are jarrah, wandoo and powderbark
wandoo. Jam (Acacia accuminata) and Rock sheoak (Allocasuarina huegeliana) are common
associated species in most areas, but land clearing has eliminated most of the smaller species once
present.
On the dissected slopes below the plateau, a mixture of marri - wandoo woodland occurs. Flooded gum
(E. rudis) and York gum (E. loxophleba) grow along the drainage lines. Eucalyptus rudis and Casuarina
obesa form riparian woodland along the Avon River and its major tributaries. Further east, the plant
communities are comprised of scattered shrubs and rock sheoak. There are woodlands of powderbark
wandoo and brown mallet (E. astringens) on lateritic plateau remnants, woodlands of wandoo and
powderbark on upperslopes, marri and wandoo on middle slopes, and York gum on lower slopes close
to drainage lines. Flooded gums line creeks and may be scattered on lower slopes.
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Woodlands of York Gum and Wandoo
Extensive areas of laterite free rocky slopes adjoin the Avon Valley and were originally covered with
wandoo and York gum woodland. This was sometimes in mixture but, more frequently segregated, with
wandoo on the upper slopes and York gum and Jam on the lower slopes.
The granite outcrops in this system support the development of a mixed low woodland of York gum and
Rock sheoak. Jam and Hakea preissii remain as small trees but introduced grasses and weeds have
replaced the original native ground layer. Along drainage lines, where saline, flooded gum are
interspersed with Casuarina obesa..
North east of the Beverley townsite, the ready erosion of the underlying predominantly gneissic rocks of
the Jimperding metamorphic belt have resulted in situations where York gum is not just confined to lower
slopes, but may occur as the sole species forming woodland over the whole landscape. Further
eastwards, where valleys broaden out and the lower rainfall results in more alkaline soils, stands of
salmon gum (E. salmonophloia) and gimlet (E. salubris) may also occur
Heath and Thickets
As rainfall decreases within the upper inland reaches of the Avon catchment, heath vegetation takes
over from the brown mallet and powderbark woodlands on the lateritic uplands. Kwongan (thickets and
heaths) occurs on the sandplains, while in lower areas tea tree thickets, or tea tree and samphire, are
dominant.
Banksia Low Woodland
Banksia woodlands can occur on transported sandsheets on lower ground which may contain swampy
pockets of tea tree and reeds. This vegetation type occurs most commonly within the West Kokeby
physiographic zone.
Salt Flats
Salt flats may be bare or vegetated with samphires. Low sand dunes also often occur in the vicinity,
along with scattered York gum and broom bush (Melaleuca uncinata).
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2.2.4.2 Remaining Vegetation
To facilitate agricultural development following European settlement, the more fertile and easily cleared
soils near the Avon River were cleared, first for grazing, and then for cropping. Clearing then gradually
extended eastwards into the lower rainfall areas and also up into the dissected slopes below the lateritic
uplands.
Today relatively small areas remain under native vegetation cover. (Maps 6 and 7) and woodlands,
particularly of York gum, are poorly represented. Approximately 27 % of the Shire of Beverley, and 12 %
of the Shire of Brookton, remains covered by relatively intact native vegetation. These figures can
however mask the extent of clearing for agriculture. In Beverley and Brookton, 85 % and 75 %
respectively of the remnant vegetation occurs within land managed by CALM. Furthermore greater than
84 % of all bush remnants on private land in both Shires are less than 20 ha in area. (Beeston et al
1994) and less than 15 % of these are fenced from stock. (Safstrom in prep).
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MAP 6
PUBLIC LAND AND REMNANT VEGETATION - SHIRE OF
BEVERLEY
MAP 7
PUBLIC LAND AND REMNANT VEGETATION - SHIRE OF
BROOKTON
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2.2.4.3 Reserves and Areas of Conservation Significance
The remaining vegetation in both Shires occurs largely within State Forest or Reserves gazetted to
ensure, among other things, the conservation of representative areas of flora and fauna habitat. In
addition, specific areas of high conservation importance have been identified and recommended for
conservation by the Environmental Protection Authority during the System 6 study (Department of
Conservation and Environment 1983) These System 6 areas and other reserves are shown on Maps 6
and 7 and are described as follows;
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Conservation Reserves recommended under System 6
C32
DALE MANAGEMENT PRIORITY AREA (Beverley)
This is within State Forest on the western side of the Shire. The recommended management priority is
for the conservation of flora, fauna and landscape, and catchment protection. The MPA contains a broad
range of features and conserves several vegetation types which have been severely affected by dieback
elsewhere in State Forest.
The recommendations have been partially implemented with the Dale Conservation Park covering 5 798
ha being established in 1992 under the Reserves Act. The area is also subject to the Alumina Refinery
Agreement Amendment Act, 1986.
C33
RUSSELL MPA (Beverley)
The recommended management priority for this area is conservation of flora, fauna and landscape.
Russell MPA contains the largest remaining area of uncut wandoo woodland in System 6. The MPA also
contains significant areas of lateritic soils supporting jarrah open forest and woodland, low open-forest of
rock sheoak and shrubland.
There are unresolved issues in relation to its conservation status. These include the Worsley mineral
lease, and the presence of long term bauxite prospects. CALM' s 1992 draft South-West Forests
Strategy recommends creation of a conservation park.
C34 GUNAPIN MPA (small section along northern boundary of Beverley)
The recommended management priority for this area is conservation of flora, fauna and landscape, and
catchment protection. Gunapin MPA conserves an outstanding range of vegetation types and species in
an undisturbed or mildly disturbed condition. It also contains the largest area of swamps in State Forest,
which support numerous species of native fauna. The recommendations have been partially
implemented with CALM's 1992 draft South-West Forest Strategy recommending recreation of a
conservation park.
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C35
SULLIVAN MPA (Beverley)
The recommended management priority for this area is conservation of flora, fauna and landscape. The
area contains Dobaderry and Goonaping Swamps which support a variety of flora and fauna.
The recommendations were partially implemented, with CALM's 1992 draft South-West Forest Strategy
recommending creation of a conservation park. Announced in October 1995, this Conservation Park
combines a number of small Nature Reserves into one park of 29 765.3 ha with 4 005 ha comprising the
former Dobaderry Swamp and Mount. Westdale Reserves within the Shire of Beverley.
C37
BROOKTON AND ALBANY HIGHWAYS (Brookton Highway through State Forest in
Shire of Beverley)
Margins of the highway constitute open space of regional significance because of their value for
conservation, for roadside display and for scientific study. It was recommended that general planning
and management recommendations for Regional Parks be applied here. The intent is being met with
agreement reached between ALCOA, CALM and EPA on a management plan. CALM's 1992 draft
South-West Forest Strategy recommends its inclusion partly within State Forest and partly in national
park.
C40
BOYAGARRING MPA (Brookton)
The recommended management priority is for conservation of flora, fauna and landscape. The MPA is
significant because it contains a large range of soils, landforms and vegetation. Also, most other valleys
similar to those within the MPA have been developed for agriculture.
The recommendation has been implemented. A Class C conservation park (Reserve 41 850) was
gazetted on 27/11/92, and covers an area of 1 209 ha.
C41
LUPTON MPA (Brookton)
The recommended management priority is for conservation of flora, fauna and landscape. The area is
particularly important as it is the only area of comparable size available for reservation which contains
certain component vegetation types and their associated fauna. No dieback has been recorded in the
MPA. The recommendation has been implemented. A Class C conservation park, Reserve 26 666, was
gazetted on 26/6/92, covering an area of 9
328 ha.
Nature Reserves - Shire of Beverley
There are seven Nature Reserves of significance in the Shire of Beverley.
Dale Conservation Park. No 39 824 and Wandoo Conservation Park. No 43 281 Refer to discussion of
System 6 areas C32 and C35 respectively.
Yenyening Lakes. Reserves number 3183 and 28 088
The reserve straddles the boundary between the two Shires approximately 28 km south east of
Beverley townsite. The reserve is approximately 1 700 ha, and comprises a natural salt lake system
which provides valuable wildlife habitat and recreational use. Further information is provided in section
2.5.5.
Other smaller reserves set aside primarily for conservation of flora and fauna are; Yandinilling Nature
Reserve No 16 142, Quajabin Reserve No 3218, and Reserve Numbers 26 897 and
41 180.
Nature Reserves - Shire of Brookton
In addition to Lupton Reserve No 26 666 which is part of System 6 recommendation C41, there are
eleven reserves of significance as follows;
Boyagin Nature Reserve No 20 610
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The nature reserve of 4 844.5 ha occurs partly in the Shire of Brookton and partly in Pingelly. The
principal plant communities are forests, low forests, woodlands, low woodlands, kwongan (heaths and
shrublands) and herbaceous plant communities. 420 plant species have so far been recorded including
2 Declared Rare Flora species.
Weam Nature Reserve No 29 322
An area of about 225 ha within the Shire of Brookton with mallet, wandoo, powderbark wandoo and
York gum and rock sheoak.
Pingeculling Nature Reserve No 36 519
A reserve of 242.8 ha within the Shire of Brookton containing lateritic breakaways with mallet, and lower
slopes with vegetation associated with more sandy soils.
Lake Mears Reserve No 12 398
Lake Mears Nature Reserve covers a wetland area of about 254 ha within the Shire of Brookton. It was
originally an intermittently fresh water wetland, with swampy tea tree and an adjacent area of woodland.
There have been modifications to the wetland which now maintains an artificially high water level for
recreational use, particularly water skiing. The lake has also gradually become more saline. Further
information is provided in section 2.5.5.
Strange Road Reserve No 36 063
The purpose of this 553.2 ha reserve within the Shire of Brookton is to conserve extensive woodlands of
wandoo and powderbark. The vegetation for the southern portion varies from open wandoo woodland
over very sparse low shrubs on the ridges, through increasing proportions of jarrah and then marri and
rock sheoak on granitic soils lower in the landscape.
Symmons Road Reserve 36 096
This 486.4 ha reserve within the Shire of Brookton is representative of the breakaway country on the
eastern flanks of the Darling Range. It contains a mixture of wandoo, powderbark wandoo and jarrah
over 50% of its area.
Private Reserve - Mrs OM Fahey and Mrs GM Fleay
This is a 237.78 ha area of remnant bushland located in an area with no nearby conservation reserves.
It thus has high conservation value over a range of soil types. The area is close to the easterly limit of
marri within the Shire of Brookton.
Other smaller reserves set aside primarily for conservation of flora and fauna are;
Kulyalling Nature Reserve No 39 379, Bartram Road Reserve No 19 740, Wills Reserve No 38 420 and
Brookton Highway Reserve No 36 742.
2.2.5
Surface Drainage, Lakes And Wetlands 2.2.5.1
Hydrology
The Shires are contained predominantly within the Avon River Basin. An exception is the area of State
Forest which drains into the Helena and Canning Rivers in the western portion of the Shire of Beverley,
and to a lesser extent within the western part of the Shire of Brookton.
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2
The Avon Basin forms a major network draining approximately 120 000 km of the Great Plateau of
Western Australia. In common with other river systems in south-western Australia, the inland portions of
the Avon are characterised by geologically old landscapes with sluggish drainage, becoming mature in
the mid sections, and sharply incised and young in the lower reaches. The Shires of Beverley and
Brookton are centred on the mature, mid section of the Avon River System. The major catchment areas
are shown on Maps 8 and 9.
In comparison with areas close to the Darling Scarp, where the river flows in a narrow and deeply
incised trench, the valley system crossing the Shire of Beverley from north west to south east is
somewhat wider. Its alignment here is considered to be geologically controlled by the presence of the
Jimperding Metamorphic belt.
In this river section, which extends northwards to Toodyay, the Avon flows through an incised landscape
with a distinct permanent river bed. It is also met by major tributaries which include the Dale and Mackie
Rivers which flow in a general north to north westerly direction. The Dale River meets the Avon
approximately 10 km north west of Beverley townsite and drains much of the western portions of both
Beverley and Brookton Shires. The Mackie River enters the Avon outside the study area just north of
Gwambygine and drains the north eastern portion of the Shire of Beverley. From these rivers numerous
smaller creeks and gullies cross the study area.
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MAP 8
MAJOR DRAINAGE SYSTEMS - SHIRE OF BEVERLEY
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The Avon River branches at a point about 15 km south east of Beverley townsite. The southern branch
extends through Brookton, roughly bisecting that Shire. The main portion of the river continues
upstream, to the east, roughly parallel to the boundary between the two Shires. The river system here
comprises broad floored, low gradient valleys largely occupied by terraces of highly weathered, coarse,
water laid sediments.
In the south eastern corner of Beverley Shire, the Yenyening Lakes (which roughly coincide with the
position of the Meckering line) mark the eastern edge of the Zone of Rejuvenated Drainage. Upstream
from these lakes there is a further decrease in river gradient associated with an increased width of the
valley floor. This contains natural salt flats and salt lakes which characterise the oldest, inland portion of
the drainage system. The north eastern portion of the Shire of Brookton and, to a lesser extent, the
eastern part of Beverley Shire, drain towards Yenyening Lakes and form part of the Zone of Ancient
Drainage.
2.2.2.5. River Flows and Flooding
Since European settlement, a number of large floods have been recorded in the Avon River. The largest
was in 1872 when much of the centre of Northam was flooded in a 1 in 100 year flood event. Smaller
floods, with water levels high enough to inundate farms in the Avon Valley and intrude into the
commercial centre of Beverley occur irregularly, but on average about once per decade.
Maps detailing areas susceptible to flooding within the Beverley townsite are available from the Water
and Rivers Commission. A report by Binnie and Partners (1985) indicates that the Shire of Beverley's
rubbish tip could be flooded in a 1 in 100 year flood. No mapping is available delineating the extent of
flood prone areas elsewhere in this Shire, or within the Shire of Brookton.
The main portion of the Avon River, downstream from Yenyening Lakes, flows strongly every winter,
although flow ceases in summer and the river becomes a series of deep pools separated by stretches of
dry river-bed. The catchment to this section is in the 450 - 600 mm rainfall zone, which produces about
90% of the flow of the Avon River (Olsen and Skitmore, 1991) and ranges from fresh (in the west where
the catchment is forested) to brackish further east.
The eastern branch of the Avon River continues upstream from Yenyening Lakes into and through the
north eastern portion of the Shire of Brookton within the Zone of Ancient Drainage. Although this area
contributes little flow in years of average rainfall (< 10% of flow), it is almost totally cleared for
agriculture, and in wet years can contribute large volumes of flood water.
The contribution from this part of the catchment is also important because it is hyper-saline and can
have a large effect on the average salinity of the Avon River, especially if salty discharge occurs at the
end of winter and the salt water is not flushed out before flow ceases and the river dries into pools
during summer. To reduce unplanned salt flushes into the Avon River, a causeway with flood gates was
built at Qualandary Crossing, on the discharge point from the Yenyening Lakes. It is used to discharge
saline water into the Avon early in Winter, when it can be flushed out of the river before summer.
2.2.5.3 River Degradation
The main forms of river degradation within the study area are;
•
salinity
•
sedimentation and erosion
•
loss of fringing vegetation
•
nutrient enrichment
Salinity
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There has been a severe increase in the salinity levels of the Avon River and its tributaries since the
area was first settled. Much of this has resulted from the extensive clearing within the catchments and
the replacement of deep rooting native trees and shrubs with shallow rooted crop and pasture species.
The result has been a rising groundwater table accompanied by mobilisation of salt to the surface.
Increases in water runoff throughout the catchment have resulted in saline groundwater and surface
waters reaching the river system.
Salinity levels within the Avon River system were originally between 400 mg/L and 3 000 mg/L (Govt of
WA 1993). Downstream of Beverley, values of between 10 000 mg/L and 30 000 mg/L were measured
during a recent survey of the Avon River (Ecoscape & Jim Davies and Associates 1996). Extreme levels
of greater than 100 000 mg/L were found in some of the permanent pools indicating that there is a
significantly saline groundwater discharge component.
River salinity is most obvious as an environmental problem in the upstream sections east of Beverley,
with salinity related death of fringing vegetation declining between Beverley and Northam. Furthermore
the salinity of river bed sediments within previously 'trained' sections of the river, may hinder any
attempts to re-establish vegetation within the channel in order to rehabilitate those sections of river (
Ecoscape & Jim Davies and Associates 1996).
Sedimentation and Erosion, - and the Avon River Training Scheme
In response to demand for flood protection within the Avon Valley, 'river training' was undertaken by the
Public Works Department between 1958 and 1970 This involved the removal of trees and debris from
within the river channel, re-aligning sections of stream bed to increase flow rates, and ripping some
compacted sections of river bed to facilitate its erosion and deepening.
The objective of the river training project was to increase the flow rate of floodwaters and thereby reduce
flood levels. In this respect the project was considered successful within the Avon Valley although there
was only a small effect on flood levels in Northam. In regard to other environmental and recreational
considerations, the consequences of the river training project have been particularly detrimental.
The Avon River was originally a series of deep pools separated by sections of river which ran in
numerous channels between islands of vegetation. With removal of vegetation from the river bed, and
ripping to promote deeper cutting, much of the sediment was made available for transport and then
deposited in the deep pools.
Today, most of the deep pools in the Avon River are filled with sediment. These pools once contained
water throughout summer and were ecologically important as refuges or focal points for aquatic fauna,
terrestrial fauna and birds. They were also aesthetically pleasing focal points for recreational use.
Between the sediment filled pools, the sections of trained river channel have now eroded to an indurated
clay bed with low vegetation regeneration potential (Ecoscape & Jim Davies and Associates 1996).
Extensive clearing of vegetation in the catchment has also contributed to the siltation of the Avon River
and its tributaries. Clearing increases the concentration and volume of surface runoff, resulting in water
erosion and sediment transport. Some areas of the river have also suffered from severe bank erosion.
To a degree this is due to stock access along unfenced sections of the river. However much of the
damage coincides with the operation of the River Training Scheme which saw the removal of vegetation
from the river banks.
Loss of fringing vegetation
Much of the land adjoining the Avon River has been cleared for agricultural purposes and in many
locations only a single line of trees separates the river from the adjoining grasslands (Government of
WA 1993). Fringing vegetation stabilises banks against erosion, provides wildlife habitats, and traps
nutrients and pollutants draining from surrounding land. River training and clearing for agriculture have
been largely responsible for loss of fringing vegetation, and the accompanying loss of wildlife.
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Nutrient Enrichment
Nutrient enrichment has become a problem in the Avon catchment with the now widespread use of
superphosphate as an agricultural fertiliser. The increase in nutrients, applied to the land and
subsequently lost in part to drainage, has corresponded with an increase of algal blooms in the
remaining river pools. Other potential sources of nutrients are stormwater runoff and septic tanks, runoff
from rubbish disposal sites, as well as high effluent land use activities, such as piggeries.
Overall Management
River degradation and other (catchment) associated problems are being addressed by the Avon River
Management Authority in conjunction with a range of government and community organisations. Actions
include foreshore vegetation protection and revegetation projects, a study of river channel morphology
and fringing vegetation, fencing and restriction of stock access, and repair of damage to stream banks.
A potential problem is that much of the river foreshore is privately owned but this is being overcome with
management agreements between ARMA and landowners. (Safstrom in prep).
2.2.5.4 Catchment Work
The development and implementation of sustainable farming systems within the catchments to the Avon
River and its tributaries, is an integral part of the strategy to improve the ecological health of the river
system. Land Conservation District Committees and associated catchment groups are the focal points
for these activities. Management plans, catchment strategies, and demonstration sites have been
achieved for areas including Yenyening Lakes, Morbinning and Westdale catchments, as well as
considerable work towards a strategy to alleviate townsite salinity problems in Brookton.
2.2.5.5 Lakes & Wetlands
The most significant lakes or wetlands within the study area are the Yenyening Lakes within the south
eastern portion of the Shire of Beverley, and Lake Mears within the north eastern portion of the Shire of
Brookton. Both areas have conservation value in relation to wildlife habitat, and both are subject to
recreational pressures.
Yenyening Lakes
The Yenyening Lakes cover approximately 1700 ha of natural salt lake system. The lakes are an
important area for wildlife habitat and recreational use. They occur at the end of long chain of salt lakes
within the Zone of Ancient Drainage and receive most of their inflow from farming country to the east of
the study area, before discharging into the north branch of the Avon River.
Water levels in the lakes have been controlled since 1928 by a causeway with flood gates at
Qualandary Crossing. This allows water to be impounded to provide for summer recreational use and
wildlife. The flood gates also enable planned discharges of saline water into the Avon in winter when it
can be flushed out of the system before summer, although the crossing has sporadically been
overtopped by floodwaters
The lakes have gradually become more saline since the 1940's and the flinging vegetation has mostly
died. Increased salinity has resulted in the loss of many species of flora and fauna, and has also seen
the spread of new species which are more adapted to saline conditions. For adjacent landowners,
increasing salinity levels are of particular concern due to salt encroachment onto nearby productive
land.
A management strategy for the Yenyening Lakes has recently been prepared by the Yenyening Lakes
Management Group in order to address the hydrological imbalance which is leading to increased
groundwater levels and salinity on adjacent farmland, and to address local management conflicts.
The management plan has produced a list of recommended actions under of the following headings;
1.
2.
3.
management of Qualandary Crossing
minimising salinity
water flows into and through the lakes to the Avon River
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4.
5.
6.
7.
8.
the management of roads,
restoration and conservation of lakeside bushlands
protection of farmlands
enhancing recreation and tourism at the Lakes
the need for research and monitoring.
In relation to rural land use, the key recommended actions are;
•
removal of artificial structures which restrict natural water flow into and through the lakes (excluding
Qualandary Crossing)
•
install drains, lined with trees, to take unused freshwater directly to storage dams, creeks or the
than lakes, rather than becoming groundwater recharge
•
discourage the discharging of saltwater into the lake
•
promote strategic revegetation and changes to farming practices where appropriate
•
encourage the fencing off of remnant bush and the replanting of salt affected areas with salt tolerant
tree species
The management plan, having been developed by a community group, has no legal status. However the
ARMA, who have statutory power in relation to river management issues, are in general support of the
plan's recommendations.
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Lake Mears
Lake Mears Nature Reserve is about 254 ha in size. It was originally an intermittently fresh water
wetland, made up of a swampy tea tree and an- adjacent area of woodland. There have been
modifications to the area which now maintains an artificially high water level for recreational use,
particularly water skiing. In common with the Yenyening Lakes it has gradually become more saline.
2.2.6
Groundwater
Groundwater occurs in fractured crystalline bedrock, in the weathered profile, and in alluvial sediments. Bore
yields are generally low, reflecting the lack of good aquifers, and are only suitable for domestic or stock watering.
the distribution of potable and saline groundwater is highly variable, with lower salinity groundwater generally
occurring only on the higher ground, if suitable aquifers are present. Groundwater in the valleys, associated with
current drainage lines, is mostly saline.
Residual sands in the Brookton to Beverley area and south west of Talbot (Map 10) are an exception and provide
a local source of potable water which is recharged from surface runoff and direct intake (Wilde and Low 1980).
These areas correspond to the West Kokeby physiographic zone (Maps 2 and 3) with many of the sands
considered to be remnants of an older Tertiary drainage system.
Of particular interest is an area between Mount Kokeby and Darkin Swamp which is an inferred former course of
the Avon River and where it is believed there is a high probability of obtaining low salinity groundwater on a local
scale (Yesertner, 1996). Within this area, land with the best potential near Mt Kokeby is the valley which Maitland
Swamp. Similarly, there is potential to the west around Forestdale extending to Darkan Swamp.
Although the areas referred to above are considered potentially prospective, it is recognised that significantly
more site-specific investigation of these areas is required to prove up their potential.
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MAP 10
2.3
REGIONAL WATER SUPPLIES
IMPLICATIONS FOR PLANNING & MANAGEMENT
This section of the report highlights the implications for land use planning and management which arise from the
inventory of the natural resources. These implications are summarised for a number of environmental planning
issues relevant to the study area.
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2.3.1
•
Management and Protection of Agricultural Land Use Systems
In accordance with State government objectives, the planning powers of both Shires should be used to
protect productive agricultural land from those developments, activities or influences that lead to its alienation
or diminished productivity. Areas where this policy should be most rigorously pursued are shown as 'high
agricultural quality' within Maps 4 and 5.
•
High quality agricultural land appears to occur most extensively in the north eastern portion of the Shire of
Beverley and within only small portions of the Shire of Brookton. The latter is largely a function of the broad
scale of resource mapping conducted for the Corrigin survey (Verboom and Galloway in prep).
•
As can be seen within Map 4 at the interface of the two major sets of mapping, most of the Corrigin survey
map units (at an intended publication scale of 1:250 000, encompass a range of both high quality and low
quality map units which are able to be distinguished by the more detailed Northam survey (at a publication
scale of 1:100 000). For this reason most of the land within the Shire of Brookton appears to have an
average, 'moderate' agricultural quality.
• To progress towards sustainable rural land use, planning and land management decisions need to be based
on an understanding of the nature of the land and its capability. The broadscale mapping contained herein
provides a basis for a general assessment of land capability, agricultural quality and land degradation hazards.
Specific development proposals however will need to be supported by more detailed survey and assessment
of actual site conditions.
• Likewise, many farm planning and land management decisions would benefit from a more detailed
assessment of the natural resources. The material herein provides an initial broad-brush assessment which
should be referred to and then supplemented by information at a level of detail which is appropriate to the
farming enterprise of development proposal.
• Without access to more detailed resource mapping, Shire planning within Brookton in relation to agricultural
land protection and land management is more encumbered than in the adjacent Shire of Beverley. This places
greater emphasis on the need for proponents of development within the Shire of Brookton to provide
appropriately detailed site assessment data in support of development applications. Likewise, there is a
greater need within Brookton for property specific land resource information to be gathered to assist farm
planning
•
The pattern of soils and hence the relative agricultural quality of the region is broadly dictated by the degree
of dissection of the original lateritic mantle of the Darling Plateau, and by the physiographic zones within the
study area.
•
In parts of the landscape where soils have developed from the upper portion of the lateritic profile, the soils
have poor physical characteristics including extensive areas of ironstone gravels, boulders and pavements
which may restrict root penetration as well as interfere with cultivation They also have low water holding
capacity and plants may suffer water stress during dry periods.
•
In parts of the landscape where the lower portions of the lateritic profile have been exposed by weathering,
the soils formed are depleted of major plant nutrients and are subject to salt accumulation. They are also
generally acid and tend to shed water resulting in a risk of erosion to soils located downslope.
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•
Soils developed on fresh 'basement' rocks are chemically more fertile than those derived from weathering of
the laterite profile, although phosphorus may still be naturally limiting to introduced plants. These soils
generally occur in areas of 'high agricultural quality'.
•
Where soils are shallow to basement rock, root penetration is restricted and plants may suffer from water
stress due to low water storage.
•
Some soils developed on terraces may suffer from winter waterlogging due to poor surface drainage, and the
presence of relatively impermeable clay subsoils.
2.3.2
•
Catchment Management and Drainage
Strategies to improve the ecological health of the Avon River are tied to the development of more sustainable
farming systems within its catchment. Land Conservation District Committees or Catchment Groups are
increasingly becoming the focal point for State Government action in this area. These committees or groups
may be of assistance to the Shires by providing advice on land management issues and appropriate
conditions for development in some areas.
•
The major portion of the study area within both Shires drains into the mid (mature) section of the Avon River.
This section of the catchment provides about 90% of the flow of the Avon River.
Changes in land use, or land management practices, within these areas therefore can have a significant
impact on water quality within the Avon.
•
Although the eastern portion of the Avon Catchment, upstream from Yenyening Lakes, contributes little flow
on years of average rainfall, it can contribute large volumes of flood water in wet years. This is mainly due to
r
the extensive amount of clearing within upstream areas, a factor which is largely beyond the influence of
land use planning and management decisions in the Shires of Beverley and Brookton.
•
Outside of townsite areas, there is insufficient information on the likely extent of flooding within rural areas.
•
Any proposals for extraction of water from the Avon River or its tributaries would need to be cognisant of
water quality which decreases with distance inland, and varies markedly with the time of year.
•
Management of river discharge from the Yenyening Lakes at Qualandary Crossing is particularly important
since it is hypersaline and can have a large effect on the average salinity of the Avon River, especially if salty
discharge occurs too late in winter for effective flushing from the mid sections of the river system.
•
The 'traditional' approach to waterlogging, of draining excess water into creeks and wetlands, is
unsustainable in many areas due to the adverse effects on the water quality and habitat value of the Avon
River System. A broader approach is therefore required which is based on maximising on-site use of water
within land use systems. In most rural situations this means planting more trees and using higher water using
crops, particularly in recharge areas.
•
The River Training Scheme, although successful to a certain degree in terms of reducing flood levels within
the Avon Valley, has had other consequences such as the sedimentation of river pools, which have
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degraded the river environment. Measures to address this situation will need to balance the environmental
benefits to be gained, against the degree of flood protection which could be lost.
•
River salinity is most obvious as an environmental problem in the upstream sections east of Beverley, with
salinity related death of fringing vegetation declining between Beverley and Northam.
•
The salinity of river bed sediments within previously 'trained' sections of the river, may hinder any attempts to
re-establish vegetation within the channel in order to rehabilitate those sections of river.
•
Loss of fringing vegetation reduces stream bank stability, decreases wildlife habitat and scenic amenity, and
reduces the potential for sediments and nutrients to be trapped and prevented from entering the river. Its
protection should therefore be a priority. A potential problem however is that much of the Avon foreshore is
privately owned.
•
In relation to future rural-residential or hobby farming it would be beneficial to require an increase in
vegetative cover on previously cleared blocks as a condition of rezoning or development, particularly along
drainage lines or wetlands margins. This not only minimises loss of nutrients which are bound to soil
particulate matter, it can also provide 'corridors' for some wildlife movement across the landscape, and
contribute to landscape amenity.
2.3.3
•
Protecting the River System and Wetlands
Due to concerns over nutrient losses to drainage, there is a need to provide adequate setbacks, for on-site
effluent disposal and land uses involving addition of fertilisers, from natural waterbodies which are sensitive
to nutrient additions.
•
In accordance with the requirements of the EPA draft Environmental Protection Policy for wetlands in the
area (EPA, 1995), development proposals likely to affect any wetlands will need to include an assessment of
their conservation value and where appropriate, a catchment or sub-catchment management plan may need
to be produced outlining proposed strategies for their protection. Although the major wetlands within the
study area are encompassed by Reserves, changes in land use elsewhere in their surface or sub-surface
catchments can affect water levels and water quality.
•
In order to fully assess possible impacts of any development proposals close to saline pools within the Avon
River, consideration needs to be given to the effect on groundwater and its relationship to river flow and
water quality.
•
In relation to Yenyening Lakes there is concern from adjacent landholders that impoundment of saline waters
within the lakes, for both recreational use and to enable planned releases of saline water, is causing salt
encroachment onto productive farmland.
•
It is likely that any activities directed at maintaining or enhancing conservation values within the Yenyening
Lakes and Lake Mears wetland areas will need to be conducted in concert with continued recreational use.
Successful implementation of management plans will require community support.
2.3.4
Salinity and Land Degradation
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•
Although subject to extensive clearing of vegetation to provide areas of productive agricultural land, the extent
of salt affected or salt prone areas is not massive, and is most prevalent in the eastern portions of both
Shires. Nevertheless because there is often a significant period of time between clearing and the onset of
salinity, remedial actions, including restrictions on further clearing, are required.
•
The general occurrence of salinity and other land degradation problems is broadly related to the degree of
dissection of the original laterite profile mantling the Darling Plateau. However the actual occurrence of many
forms of land degradation will be determined by site specific land management and topographic factors. Due
to the scale of mapping on which interpretations of land degradation hazards are based, caution should be
exercised in their application to planning decisions. Site specific applicability should always be checked.
•
Salt storage occurs in the deeply weathered lateritic profiles which are common to upland areas. Clearing in
these areas has the potential to raise watertables and mobilise soluble salts which will affect lower portions of
the landscape.
•
Where relatively shallow permeable soils have developed from fresh bedrock, as in the main valley and on the
sides of the Avon River, the deep weathering zones which contain the high salt storage are largely absent. As
a result there is minimal salinity in these areas except for salts in transport along major streams and rivers.
•
In the broad flat eastern valleys, where groundwaters have risen to or near the surface, large areas of what
were previously productive agricultural soils have been rendered largely unsuitable for agriculture due to high
salt concentrations and waterlogging.
•
The development of farming systems with greater use of deeper rooting, higher water using tree and crop
species, in preference to broadacre pasture and shallow rooting crop species, is required to at least partially
redress the salinity problem.
•
The occurrence of soil erosion will be largely determined by land use and management factors, however
some areas are more susceptible than others. These areas, identified within Table 2, have special land
management needs.
2.3.5
•
Protecting Remaining Vegetation
The agricultural landscape within the Shires of Beverley and Brookton has been severely depleted of its
original native vegetation cover in order to use the land resource for agriculture.
•
The majority of bush remnants on private land in both Shires are less than 20 ha in area, and hence many
will be less than a 'viable size' for preservation of vegetation communities and associated flora and fauna
habitats.
•
Remnant vegetation plays a number of important roles as follows;
-
provides a barrier against wind and water erosion
-
assists prevention of waterlogging and nutrient build up in watercourses - contributes to scenic amenity
-
provides habitat for fauna, particularly avifauna
-
provides areas for passive recreation.
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•
Indirect pressures associated with increasing numbers of residences near reserves and conservation parks
will result in a greater need for management in areas such as fire control, catering for recreational demands,
control of rubbish and weeds, control of access, and preventing the spread of dieback disease.
•
Rural land adjacent to Reserves can also be adversely affected through the potential for fire and the
competition for feed between grazing stock and native wildlife.
•
In evaluating any land use planning proposals likely to involve the clearing of areas of remnant vegetation,
consideration needs to be given not only to the overall amount of vegetation remaining in the Shire, or within
a particular subcatchment, but also to the type of vegetation concerned and the degree to which it is
represented within those remnants.
•
Certain vegetation types are more significantly depleted than others and hence provide a stronger case for
protection. For example, areas of York gum woodland vegetation type are very poorly represented in
Reserves
•
Reserves and other areas of conservation significance shown in Maps 6 and 7 can effectively be considered
exclusion zones when considering future land use potential in the study area. However their presence and
conservation values need to be taken into account in relation to adjacent development or land use proposals.
Particular matters of concern include fire risk, weed infestation and spread of dieback.
2.3.6
•
Agricultural Diversification
Diversification of farming systems is generally encouraged by Agriculture WA, particularly for wool farmers.
This is in response to an analysis of long term market prospects which indicate declining prices in real terms.
(Department of Agriculture 1993).
•
While diversification into cropping is appropriate for areas of high quality agricultural land, diversification into
more intensive, or less 'tested' forms of agriculture may be more appropriate for areas of moderate
agricultural quality. This is particularly so if a trend towards new agricultural activities is initiated mainly
through small scale, or part-time farming ventures on 'hobby farming blocks.
•
This existing (historical) pattern of subdivision has created many lots in the 40 - 60 ha size range which may
be suitable for diversified agricultural activities or hobby farming.
•
Climatic conditions within all but the eastern most portions of both Shires are conducive to a range of cropping
enterprises. These include wheat, barley, oats, lupins, canola, and field peas.
•
In relation to the potential for horticultural activities, opportunities are primarily limited by water supply more
than climatic factors, but winter chilling requirements and frost susceptibility also need to be considered
•
Areas of residual sands within the West Kokeby physiographic zone, to the west and south of Beverley, are
considered potentially prospective for groundwater and hence may provide future opportunities for small-scale
irrigated agriculture.
•
Significantly more site-specific investigations, both of water supply and soils, are required to prove up any
areas as being suitable for irrigated agricultural use.
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•
Given the generally modest prospects for significant development of irrigated agriculture, it is likely that only
small, part time, ventures would initially be established which may, in time, develop into a viable local industry
supplementing traditional mainstay agricultural operations.
2.3.7
Areas Suitable for Rural -Residential Development
• Not forsaking the need to ensure unsewered residential development occurs without adverse environmental
impacts, rural - residential developments need to be sited away from areas of very good quality or 'prime'
agricultural land.
•
Land capability is not the sole determinant of whether or not particular areas are 'suitable' for subdivision to
cater for demand for rural-residential or hobby farming blocks. Nevertheless, the nature and magnitude of
environmental planning issues identified in this report dictate that capability factors be strongly considered.
The value of land capability assessment is in its identification of the relative severity and nature of physical
land use limitations which can then be addressed through conditions of development or subdivision.
•
As a general rule however, particular care should be exercised in locating any developments so as to avoid
direct impacts on 'very low' capability land, and to address land use limitations within 'low' capability areas.
For some proposals in low capability areas, development and management requirements may be prohibitive.
•
Ironically, some caution should be exercised in allowing rural - residential development in areas identified by
proponents as having a particularly high capability for the associated activities of housing and on-site effluent
disposal. This is because such land conditions, which include free draining, nutrient retentive soils on flat to
gently undulating terrain, also describe the characteristics of good quality or 'prime' agricultural land.
Therefore where protection of productive farmland from rural - residential development is a priority, the land
which is most suitable for rural - residential use is probably land of 'fair' capability, or 'moderate' agricultural
quality.
•
Fire hazard is a concern of particular importance when siting rural-residential developments in proximity to
large areas of remnant vegetation. Within the study area this means in proximity to the areas of State Forest
and Reserves, which occur predominantly in the western sectors of both Shires.
•
Outside areas serviced by scheme water, prospective purchasers of subdivided lots need to be advised that
they will be obliged to make their own arrangements to provide a satisfactory potable water supply. Should
domestic water supply need to be obtained solely by harvesting rainwater, Agriculture WA data (Laing, 1990)
provide an indication of the house or shed roof areas required. Within the Beverley - Brookton area this
2
information indicates that a storage tank of 110 kL capacity, and fed by a 600 m rooftop catchment
(galvanised iron), is required to satisfy a water demand of 600 L of water per day with 98% reliability. This
demand is close to the water needs of an average household of four people.
•
In many situations, domestic water supply is likely to be based on a combination of rainwater harvested from
rooftop catchments, and groundwater bores. Where this occurs, large lot sizes are generally recommended to
maximise the probability of obtaining a suitable source of groundwater as a supplementary water supply.
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2.3.8
•
Protection of Mineral Resources and Basic Raw Materials
There are no occurrences of metallic minerals within rural portions of the study area that are
considered particularly prospective.
•
There are only scattered occurrences of basic raw materials suitable for road construction purposes
Within the Shires and this can place pressure on the Department of Conservation and Land
Management for access to reserves for extraction purposes.
•
Exploration licences issued by the Department of Minerals and Energy throughout the Study Area
are illustrated on Maps 15 and 16.
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