Oral Presentation 9th Australian Stream Management Conference 2018

Dredging up the past: what are the current implications for Victorian rivers from historic gold dredging? (#13)

James Grove 1 , Jodi Turnbull 1 , Susan Lawrence 1 , Peter Davies 1 , Ian Rutherfurd 2 , Ewen Silvester 3
  1. Archaeology and History, La Trobe University, Bundoora , VIC, Australia
  2. School of Geography, University of Melbourne, Parkville, VIC
  3. Department of Ecology, Environment and Evolution, La Trobe University, Wodonga, VIC, Australia

Across Victoria > 100,000,000 m3 of sediment was excavated by bucket dredging between 1900-1914.  River channels were moved, mined and then replaced in their original location.  Meanwhile, on the floodplain sediment and soil profiles were altered.  This left layers of coarse gravel deposited on, or near, the surface.   The environmental legacy of this assault is evaluated in this paper, focusing on an understanding of the period of greatest activity, between 1900-1915.  No regulation existed from 1900 – 1905, with sludge at these leases continuing to enter the river system for the mines life.   The Beechworth mining district had the most of leases, many of these on the Ovens River.  The records suggest that 2,060 ha could have been worked in Victoria, equivalent to 1,688 soccer fields.   The worked areas were often impounded sections of floodplain that floated dredge pontoons, usually in the partly confined reaches of rivers.  The buckets dug down to a palaeochannel deposit containing gold.  Working back and forth linearly across the lease they excavated, sorted and treated (sometimes with mercury) the sediment.  Current LiDAR shows these linear features from the elevation differences in the spoil mounds.  The resulting landscape could be an improvement if the area has previously been mined.  However, 45 % dredged land in the Ovens is estimated to be only suitable for grazing and pine plantations.  Preferential export of subsurface fines, combined with settlement has caused sinkholes.  Whilst other mining methods may have liberated more sediment, and associated contaminants, the legacy of dredging has been to create large areas of land near to rivers that will never be restored and are extremely difficult to rehabilitate.  Catchment managers should, therefore, know the location and history of dredged sites.

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