| Darling Scarp | |
| Other Name: | Darling Range |
| Country: | Australia |
| Region Type: | State |
| Region: | Western Australia |
| Highest: | Mount Cooke |
| Elevation M: | 582 |
| Formed By: | Darling Fault |
| Period: | Cenozoic |
The Darling Scarp, also referred to as the Darling Range or Darling Ranges, is a low escarpment running north–south to the east of the Swan Coastal Plain and Perth, Western Australia. The escarpment extends generally north of Bindoon, to the south of Pemberton. The adjacent Darling Plateau goes easterly to include Mount Bakewell near York and Mount Saddleback near Boddington. It was named after the Governor of New South Wales, Lieutenant-General Ralph Darling.
The feature was first recorded as General Darling Range by Charles Fraser, Government Botanist with Captain James Stirling aboard in March 1827.
Maps from the 1830s show the scarp labelled "General Darlings Range"; this later became Darling Range, a name by which the formation was still commonly known in the late 20th century despite common understanding of it being an escarpment. There is also a tendency to identify the locations on or to the east of the scarp as being in the "Perth Hills" (or simply "The Hills").
The earliest traverses by British settlers in the Swan River Colony occurred in the 1830s. The best known of these is the expedition of Ensign Robert Dale, who appears to have gone from a point near Guildford, to the south side of Greenmount Hill and up through the Helena Valley.[1]
The Darling Scarp originated as the local expression, in the Perth area, of the extensive Darling Fault, a major and ancient geological discontinuity separating the Archaean Yilgarn Craton in the east from the younger Pinjarra Orogen and overlying Phanerozoic Perth Basin to the west. The Darling Fault is exposed for over, from the area east of Shark Bay, to the southern coast of Western Australia east of Albany. The location of the scarp must once have coincided with the location of the fault, but the scarp has since eroded about eastwards. The original location of the scarp is indicated in places by an unusual landform known as the Ridge Hill Shelf.
The Darling Plateau is covered by lateritic materials that cover the underlying geology.[2]
The Archaean granites and gneisses of the Yilgarn Craton form the high ground of the Perth Hills and can be observed in road cuts, with good examples in the Mundaring Weir area. The only exposed sediments of the Perth Basin, west of the fault, are of Cenozoic age, and are composed of materials such as sandy limestone, travertine and dune sand on which the city of Perth is built, including sand dunes of Pleistocene age formed during the last glacial period.
This area is also a distinct physiographic section of the larger Yilgarn Block province, which in turn is part of the larger West Australian Shield division.
The Scarp, like the rest of south west Australia, has a Mediterranean climate, with mild rainy winters and warm dry summers. Average annual rainfall is 1300 mm along the scarp, declining to the east and north.[3]
Often the Bureau of Meteorology identifies different weather for "the hills" in comparison to that of the Swan Coastal Plain.[4]
Also, in traditionally hot summers, strong easterly winds travelling across the scarp have presented serious issues for planes using the Perth Airport because of the alignment of the runways.[5] On 2 September 1999, the number one engine of a Qantas Boeing 747, en route from Sydney Airport coming into land on Runway 06/24, struck the runway surface upon landing, due to wind shear caused by rolling winds on the Darling Scarp. In addition, orographic uplift is produced when rain clouds move over the hills, giving higher rainfalls in settlements in the ranges compared with their coastal neighbours.
The scarp is part of the Jarrah Forest bioregion. The natural vegetation of the scarp is predominantly jarrah–marri forest, characterised by jarrah (Eucalyptus marginata) and marri (Corymbia calophylla), with bullich (Eucalyptus megacarpa) and blackbutt (Eucalyptus patens) in the valleys.[3] The Darling Range ghost gum (Eucalyptus laeliae) is endemic to the western slopes of the scarp.
Heath is found on granite outcrops. Low woodlands of Banksia grow on sand sheets.[3]
Native mammals include the quenda (Isoodon fusciventer), chuditch (Dasyurus geoffroii), woylie (Bettongia penicillata ogilbyi), and brush-tailed phascogale (Phascogale tapoatafa wambenger). Quokka (Setonix brachyurus) and western ringtail possum (Pseudocheirus occidentalis) are often restricted to riparian areas.[3]
The Darling escarpment has been exploited for stone quarries, forestry and bauxite mining. Extensive timber railways and timber mills and the supporting communities existed along the escarpment because of the high quality jarrah forests.[6]
In the early twentieth century, most of the main rivers flowing off the escarpment had mainly been used for dams for water supply for metropolitan Perth. The dams on the scarp include:
The only free flowing water from the Darling Range in the Peel Region is the Dirk Brook in Keysbrook and the Murray River.
The scarp also defines the easternmost limit of the various aquifers present in the Perth Basin sediments, most notably the Southwest Yarragadee Aquifer. The scarp forms a divide between the hypersaline groundwaters typical of the Yilgarn Craton basement from the fresh ground waters of the Perth Basin. Some dams along the scarp are contaminated by seepage of saline water from the granite into the base of the dam's water column and must be periodically flushed to preserve water quality.
Also in the early to mid-twentieth century numerous rock quarries existed on the edge of the escarpment - visible and affecting both the aesthetics and the environment of the escarpment.
In the area where the Helena River emerges from its valley to the sandplain, there are still four quarries evident, despite being unused as quarries for fifty years or more. Mountain[7] and Stathams[8] quarries are now managed as rock climbing locations.
There have also been visible quarries on the scarp in the Gosnells and Herne Hill areas.
Legislative restrictions upon such developments were initiated in the late twentieth century to prevent further visible scars on the western face of the scarp.
See also: Bauxite mining in Australia.
In the late twentieth century, the proving of bauxite deposits correlating to the extensive jarrah forests saw wide-ranging protests against the proposals to mine the forests. Campaign to Save Native Forests was one group to oppose the activity.
The lengthy process of protest forced the government and miners to check their original proposals, and wide-ranging processes to guard segments of the jarrah forests from mining ensued.
The current mining activity in the region is extensive - the main mines being Huntly and Willowdale.[9]
The building and developing of rail access across the scarp developed three separate main routes over eighty years.[10]
The localities or suburbs on the "edge" of the scarp are those that sit at its western edge, and in most cases command excellent views of the Swan Coastal Plain:
The suburbs near Midland and Kalamunda are often referred to as the Perth Hills.
The suburbs to the south of Kalamunda are the locations of the main Perth Metropolitan television station transmission towers. There is also another site at Mount Lennard near Collie that Services the Southwest areas including Bunbury.
Also in the late twentieth century, dieback affecting jarrah timber in particular infected large tracts of the forest. Currently only the restriction of vehicle access has proved effective in slowing the spread of this disease. This gained greater acceptance and publicity through the decision to allow Rally Australia to operate along services roads provided that the vehicles had a thorough wash including the under carriage at the end of each stage.
In late 2004, the largest bushfire in the northern Jarrah Forest for at least 100 years created significant issues for the forest as well. As a result of this fire intensity the Government increased the volume of controlled burns along the entire escarpment to reduce the buildup of flammable materials.
In the early 2000s, Greenmount National Park and John Forrest National Park were repeatedly burnt by bushfires - in most cases through suspected arson.
A network of reserves of crown lands on the escarpment have been connected into a regional park to maintain and conserve parts of the escarpment.
In most cases the reserves or parks had individual names prior to being incorporated into the larger park, for example the Serpentine National Park, John Forrest National Park and the Greenmount National Park, or were simply known as State Forests (e.g. State Forest No.42).
Following a change in 2005, the separate parks have been known as the "Parks of the Darling Range", and take up 23,948 hectares on the scarp.[11] Further in August 2008 the parks were given indigenous names:[12]