SW4 Deans Marsh, Rockbank - Intermittent Lakes

This information has been developed from the publications:

Sites of Geological and Geomorphological Significance in the Western Region of Melbourne (1986) by Neville Rosengren
Sites of Geological and Geomorphological Significance on the Coast of Port Phillip Bay (1988) by Neville Rosengren.
Sites of Geological and Geomorphological Significance in the Shire of Otway (1984) by Neville Rosengren.

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 (external link) for details of geological heritage reports, and a bibliography.

Location	Sydenham West - 948215. Shire of Melton. North of Western Highway at Rockbank.	SW4 - Intermittent Lakes, Deans Marsh, Rockbank
Access	Western Highway.
Ownership	Commonwealth land (Defence Department, Rockbank Signal Station) and private land.
Site Description	Between Kororoit Creek and the Western Highway are several enclosed depressions on the surface of the lava plain. The depressions appear to be due to the original configuration of the contours of the lava and are an integral part of the original basalt terrain.
	The two westernmost depressions, that comprise this site, are generally marshy, indicating they are fed from groundwater springs; they are intermittent rather than ephemeral lakes. The lake water is slightly brackish and alkaline, and there is a concentration of the sulphate ion. There is no surface water exchange between the lakes but the northern lake is partly artificially drained to Kororoit Creek. It is likely that there is a complex hydrological regime of these lakes related to water levels of Kororoit Creek.
Significance	Regional. Although there are many enclosed depressions on the Werribee Plains, most have been severely disturbed by draining, grazing, reclamation or other processes. The two wetlands at this site are therefore important remnants to illustrate the formerly complex drainage and surface water distribution of the plains. They should be retained to allow studies of water quality and hydrological regime. The shorelines of the lakes are low and rocky and illustrate the weathering of basalt boulders in a saline wetting and drying environment.
Management	Class 1. The lakes need to be excluded from disturbance associated with adjacent land use. As most of the surrounding area is being subdivided, it is important that planning controls prevent the draining, filling, or reclamation of these two remaining wetlands, and ensure that street drainage or other urban runoff is not diverted into them. The drain from the northern lake should be closed. The lakes should be seen as a positive factor providing important terrain variation in an otherwise uniform landscape.
References	Shugg, A. (1980). Disturbed Drainage and an Ephemeral Lake on the Basalt Plains, Rockbank (Kororoit Creek). Unpub. Reports Geol. Survey Vic. 108.

Page top