Protección contra incendios

The Avon Province lies largely on the Yilgarn Craton, (part of a large Archaean shield) and most of the area consists of lateritic plateau, or its remnants, overlying a granitic basement. There are seven zones including the Zone of Ancient Drainage (Figure 2.2.4) and the Zone of Rejuvenated Drainage (Figure 2.2.5) which cover a significant proportion of the land cleared for agriculture.

In the south-west, significant areas of native forest remain.

221 Coastal Dune Zone 222 Dandaragan Plateau Zone 223 Victoria Plateau Zone 224 Arrowsmith Zone 225 Chapman Zone 226 Lockier Zone 24 Stirling Province

241 Stirling Range Zone 242 Albany Sandplain Zone 243 Jerramungup Plain Zone 244 Ravensthorpe Ranges Zone 245 Esperance Sandplain Zone 246 Salmon Gums Mallee Zone 247 Boorokup Lakes Zone 25 Avon Province

251 Leeuwin Zone

252 Donnybrook Sunkland Zone 253 Eastern Darling Range Zone 254 Warren-Denmark Southland Zone 255 Western Darling Range Zone 257 Zone of Rejuvenated Drainage 258 Zone of Ancient Drainage 27 Murchison Province

LEGEND

Figure 2.2.3 The provinces and zones of south-western Australia.

Zone of Ancient Drainage

An extensive undulating plain characterised by a gently undulating plateau, with wide divides, long gentle sideslopes and broad valley floors (2-10 km wide), which have been in-filled by alluvium and colluvium. Drainage is into chains of salt lakes on valley floors which are a remnant of an ancient drainage system that flows only in very wet years. The valley floors have very low gradients, often 1:1,500 or less. The western boundary is the Meckering Line (Mulcahy 1967).

Soils are mainly formed on laterite, truncated laterite, parna (mainly from lake beds), rock weathered in situ (granite, greenstone, dolerite), colluvium and alluvium.

There is a regular soil pattern on divides, sideslopes and valley floors (Figure 2.2.4). Soils are predominantly yellow deep sands and sandy gravels on the catchment divides, with grey shallow and deep sandy duplex soils on the valley slopes, and calcareous loamy earths and alkaline shallow duplex soils on the valley floors.

Land resource information is available for Merredin (Bettenay and Hingston 1961, 1964), Kellerberrin (McArthur 1992), Bencubbin (Grealish and Wagnon 1995), Northam (Lantzke 1992; Lantzke and Fulton 1993) and Lake Cairlocup (Harper 1994).

Steep rocky hills Thin midslope

Rocky, red, loamy Avon Valley slopes

red-brown loams and grey loamy sands

Steep rocky hills

Breakaway

Broad, flat, valley floors with heavy red

and grey soils

country Broad, flat, sand over clay valley floors

Gentle lower slopes containing pale sand and loamy sand over clay soils

Long hillslopes containing hardsetting grey to brown

sandy loams

Yellow and grey, un-dulating sandplain of the Eastern

Wheatbelt

Figure 2.2.4 Idealised block diagram showing the soils in the Zone of Ancient Drainage in relation to landscape position (from Lantzke and Fulton 1993). This diagram was developed for the Cunderdin-Tammin area.

The proportion and types of soil may vary in other areas.

Zone of Rejuvenated Drainage

Gently inclined rises and low hills are mainly formed on dissected laterite, with narrow divides and only small scattered lateritic remnants. Some areas formed on acid igneous and metamorphic rocks weathered in situ (e.g. Avon Valley). It is more dissected than the Zone of Ancient Drainage, with narrower valley floors which contain creeks and rivers that flow every winter.

Most of the landscape has formed on the mottled and pallid zones of the laterite profile, or from freshly exposed rock rather than intact laterite. This zone is bounded by the Meckering Line in the east and the Darling Range to the west.

Figure 2.2.5 Idealised block diagram showing the soils in the Zone of Rejuvenated Drainage in relation to landscape position (from Lantzke and Fulton 1993). This diagram was developed for the Northam area. The proportion and types of soil may vary in other areas.

At a superficial level there is a straightforward soil pattern from the uplands to the valley floors. But there is a high spatial variability of important soil properties affecting production (e.g. subsoil permeability), especially on the sideslopes, because of differential erosion and deposition. Refer to Figure 2.2.5.

Land resource information is available for York (Mulcahy 1959; Mulcahy and Hingston 1961), Northam (Lantzke 1993; Lantzke and Fulton 1993), Murray Valley (McArthur et al. 1977) and Tutanning Nature Reserve (Nyagba 1976).

Eastern Darling Range Zone

A gently undulating to undulating lateritic plateau, which is partly dissected by eastward flowing streams to form shallow valleys with broad (1 to 3 km) flat valley floors. Tributary streams flow into the major rivers which dissect the Darling Range.

This zone forms an intergrade between the Western Darling Range Zone and the Zone of Rejuvenated Drainage.

Soils are mainly formed on laterite (over granite), truncated laterite, rock weathered in situ (granite), colluvium and alluvium. Soil pattern is closely related to topography and degree of erosion. On the uplands, sandy gravels and loamy gravels are dominant, while on the valley slopes there is a range of soils, depending on whether they are formed on truncated laterite (sandy gravels, grey deep sandy duplex soils, pale deep sands) or granite weathered in situ (brown loamy duplex soils, red deep sandy duplex soils).

Land resource information is available for west of Bolgart-Beverley (Lantzke and Fulton 1993), Murray Valley (McArthur et al. 1977) and the southern Darling Range (Tille 1996).

Western Darling Range Zone

An extensive undulating lateritic plateau (Darling Plateau) which is largely intact. The plateau has deeply incised valleys where it has been dissected by the major river systems of the inland zones. The western boundary is the Darling Scarp. To the east there is a gradual increase in dissection as this zone grades into the Eastern Darling Range Zone.

Soil pattern relates to the amount of erosion and valley forms (Mulcahy et al. 1972). Soils are mainly formed on laterite (mainly over granite, some dolerite) and colluvium (mainly from laterite) on the plateau and from rock weathered in situ (granite, gneiss, dolerite) in the incised valleys. On the plateau surface, gravels overlying duricrust are dominant (e.g. shallow gravels, moderately deep sandy gravels and

loamy gravels). Pale deep sands and yellow deep sands are also found. Loamy earths and brown loamy duplex soils have formed on freshly exposed rock in the valleys.

Land resource information is available for the Darling Range (Mulcahy et al. 1972; Churchward and McArthur 1980; King and Wells 1990), Wungong area (Churchward and Batini 1975), Helena River catchment (Mulcahy et al. 1972), Collie (Bettenay et al.

1980), Cobiac Valley (Siradz 1985), Bridgetown-Greenbushes (Finkl 1971; Finkl and Churchward 1976) and the southern Darling Range (Tille 1996).

Orchards and grazing country at Mullalyup, a dissected valley through the lateritic plateau in the Western Darling Range Zone (P. Tille).

Donnybrook Sunkland Zone

Level to gently undulating lateritic plateau formed on sedimentary rocks of the Perth Basin. Shallow valleys occur where the plateau has been dissected by the Blackwood, Capel and Preston Rivers. Includes the poorly drained Scott River Plain in the south.

Soils are mainly formed on laterite (over sedimentary rocks), colluvium (mainly from laterite) and alluvium.

Sandy gravels with some small areas of shallow gravel, pale deep sands and yellow deep sands on both the plateau and the dissected areas. On the Scott River Plain, pale deep sands, brown deep sands and wet soils are common.

Land resource information is available for Nannup (Churchward 1992), Wellington-Blackwood (Tille 1996) and Busselton-Margaret River-Augusta (Tille and Lantzke 1990).

Warren-Denmark Southland Zone

This zone falls gently from the southern edge of the Blackwood River catchment to the south coast. It includes lateritic plateau, dissected terrain formed on granite and gneiss, and swampy coastal plains. Some areas of the plateau are overlain by sedimentary deposits.

Soils are formed on laterite, colluvium (mainly from laterite), rock weathered in situ (gneiss, granulite) and alluvium. Dominant soils are loamy gravels and sandy gravels with pale deep sand and deep sandy duplex soils on the plateau. Red-brown and yellow-brown loamy gravels and friable red-brown loamy earths are found on rock weathered in situ. Pale deep sands, brown deep sands and wet soils are found on the poorly drained flats.

Land resource information is available for Manjimup (Churchward 1992), Northcliffe to Albany (Churchward et al. 1988) and Pemberton (McArthur and Clifton 1975).

Leeuwin Zone

This zone has formed on the Leeuwin Block, which is dominated by a lateritic plateau. The plateau has been dissected by a number of valleys, exposing the underlying granitic basement. There are coastal dunes and limestone ridges on the western margin. Extends between Cape Naturaliste and Cape Leeuwin.

Soils include gravels, friable red-brown loamy earths, yellow deep sands and deep calcareous sands (Tille and Lantzke 1990).