Site 28 Craigieburn East - Stony Rises, Gilgai (Soil Mounds)

This information has been developed from one or more of these publications:

Sites of Environmental Significance in the Flood Plain of the Upper Yarra Valley Region (1983) by Neville Rosengren, Douglas Frood and Kim Lowe (as part of a study of Sites of Environmental Significance by the University of Melbourne for the then Upper Yarra Valley and Dandenong Ranges Authority).

Geological heritage sites, including sites of geomorphological interest and volcanic heritage sites, are under regular revision by the Geological Society of Australia, especially in the assessment of significance and values.Reference should be made to the most recent reports. See the Earth Science Heritage section of the Geological Society of Australia website for details of geological heritage reports, and a bibliography.

Location:	YARRA 5000/03.14 E19600 N34200 to E19500 N35000
	A large site including the channel and an irregular area on the left bank of the Merri Creek south of Craigieburn East Road.
Access:	Craigieburn East Road, Rushwood Drive.
Ownership & Municipality:	Private Land, City of Whittlesea.
Site Description:	This site has diverse topographic and soil patterns and has a complex geological and geomorphological history. It lies immediately south of the Silurian inlier of Summer Hill and the Merri Creek flows along the western margin of a lava flow from Hayes Hill. Ridges and rocky hummocks are separated by flat areas with significant gilgai microrelief. The low hills and ridges are stony rises, originally areas of rugged surfaces that have been subdued by weathering. Gilgai area phenomenon developed in soils with substantial component of clays that swell when wet. Here they are in the form of roughly circular mounds up to 1 m in diameter with rims 30 cm to 40 cm high. The soils of the gilgai areas have been described by Frood (1993). The Merri Creek valley has distinct alluvial and bedrock terraces and a series of cliffs and bluffs marking the edge of the inlier valley.
Significance Rating:	Regional.
	This is an area of complex terrain and soils. It has been relatively little disturbed in comparison with adjacent similar sites which have been quarried, cultivated, drained or otherwise physically altered. It is a clear example of a weathered stony rise and illustrates the character of the originally rugged topography of the flow surface. Gilgai phenomena are uncommon in the Merri Creek catchment as most have been modified by agriculture or construction. The site is a good location t show the geomorphological variation of the valley including the incised rocky channel, old higher level channel and different types of terraces.
Site Sensitivity:	Class 1.
	The gilgai terrain is a subtle topography that is sensitive to disturbance, particularly by cultivation or construction. Gilgai soils also pose a problem for construction due to their shrink-swell potential. Road and building location need adequate site investigations to determine possible soil hazards.
References:	Frood, D. 1993, Vegetation of the Native Grasslands in the Merri Creek Valley, Outer Melbourne Area. Ecological Survey Report No. 42. Dept. of Conservation and Environment – Victoria.

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