Patterns of Debris Movement: From an Urban Estuary to a Coastal Embayment

Article by Scott P. Wilson and Stephen J. Randall,

Centre for Environmental Restoration and Stewardship

Australian Catholic University, 2005

Article excerpt:

“Beach or shoreline surveys are the most common form of quantifying human generated debris. They reveal a lot about the amounts and types of persistent wastes that end up in these environments, however, the movement and specific source of these items have not commonly been categorically defined. Sourcing debris items has been difficult due to their mobile nature (Williams and Simmons 1999) and usually left to an individual’s discretion. Some items can easily be identified and sourced (e.g. fishing nets), other items are reliant on weight of evidence to determine where they originated. Statistical techniques and modelling have shown some success in determining sources (Kubota 1994; Belas et al. 2001; Tudor et al. 2002) but are reliant on background studies or site specific testing to verify results.

Water–based surveys of floating debris provide valuable information on distribution patterns and extent of movement of these types of items (Moore et al. 2001) but the residence times and individual patterns of movement cannot be examined by this method alone. One approach that goes some way to answering these issues is through tagging studies. This has been applied to selected items on coastal beaches (Bowman et al. 1998; Johnson & Eiler 1999; Williams and Tudor 2001) but does not target the main source of coastal debris, particularly in urban areas, the rivers. Bulk movement patterns of selected riverine litter have been detailed by Williams and Simmons (1997), however there have been few studies looking at individual movement patterns of a range of debris types from river/estuary sources. To this end, tracking of debris from a potential source to an end destination was undertaken along the Cooks River and in Botany Bay, Sydney. The importance of tidal movement, riparian vegetation and rainfall is highlighted.”

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