Cabbage Tree Creek
Recreational Waters Investigation
Final Summary Report
Prepared for
Queensland Urban Utilities
& Brisbane City Council
Prepared by
Built and Natural Environment
City Projects Office, Brisbane City Council
Executive Summary
Queensland Urban Utilities (QUU) and Brisbane City Council (BCC) collaborated to
undertake an investigation into bacterial contamination in Cabbage Tree Creek. The
sampling program aimed to identify potential source locations and type of bacterial
contamination in the lower reaches of Cabbage Tree Creek (refer Figure 1: map of study
area).
Specific objectives of this project were to:
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Discover the potential location and origin of the contamination; and
Clarify the persistence of the contamination within the waterway.
Sampling was conducted between January 2012 and May 2012, targeting two flow
events and two ambient conditions as follows:
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Rainfall event 1 – January 2012;
Rainfall event 2 – April – May 2012;
Ambient sample 1 – 3 April 2012; and
Ambient sample 2 – 25 May 2012.
In order to better understand the catchment water quality over time, the physico-chemical
and microbial characteristics from this study were supplemented with all available historic
data. After combining all available information, the following observations were possible:
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The occurrence of elevated Enterococci in multiple drains and tributaries shows that
there are differing sources of faecal contamination in each sub-catchment of
Cabbage Tree Creek. Analysis of sterols confirmed that the elevated Enterococci
concentrations contained some faecal input from horses, cattle, fruit-eating native
species (e.g. birds, bats, possums) and humans. Having said that, the predominant
contribution to Enterococci levels was identified as being of animal origin.
The characteristics of freshwater tributaries are quite different to estuarine sites
because they are influenced by different ecosystem processes. Estuarine sites not
only reflect the cumulative effects of multiple tributary contaminants but also the
effects of tidal influence.
Results in this study showed that there was spatial and temporal variability in
Enterococci concentrations across tributary sites, which is to be expected given the
differing diffuse and point source inputs in each sub-catchment.
At the most downstream site, there was persistence of Enterococci concentrations for
6 days after Event 1. These levels decreased after 10 days. This is likely to be a
result of the lag-time from continuing upstream flow inputs rather than local sources
at that site. Following Event 2, this site recovered to background levels within 2 days.
This report provides a number of recommendations with regard to: infrastructure
management in lower Cabbage Tree Creek, improving water quality in high priority
tributary areas, undertaking awareness programs in the local area, promoting alternative
strategies for water management in areas of potential contamination, and using sciencebased catchment management techniques to improve water quality throughout the
broader catchment.
Cabbage Tree Creek Recreational Waters Investigation
Final Summary Report
Recommendations
The following recommendations are provided for lower Cabbage Tree Creek:
Infrastructure and Operations
1. Continue to improve risk assessment framework for sewer network and utilise it to
inform infrastructure maintenance and investment priorities.
2. Continue to improve understanding of the frequency and duration of sewage overflow
events during wet weather.
3. Review the management of stormwater in the vicinity of Curlew Park.
4. Continue to undertake the recreational waters city wide human health monitoring
program to monitor on-going Enterococci levels within CTC.
Research
5. Better understand potential upstream enterococci contamination sources. Use
findings from research organisations that are currently doing work in upper Cabbage
Tree Creek catchment.
6. Investigate the feasibility of utilising new technologies that would enable water quality
treatment at the end-of-system for tidally influenced drains.
7. Work with research organisations to understand the potential human health risks
associated with Enterococci contamination.
Community Engagement
8. Engage with the equine community in the lower Cabbage Tree Creek catchment on
the findings of this report.
9. Undertake community education / awareness of the causes of microbial
contamination in lower Cabbage Tree Creek.
Land Management
10. Ensure findings of report are used in future catchment management and planning.
Cabbage Tree Creek Recreational Waters Investigation
Final Summary Report
Figure 1: Map of Cabbage Tree Creek catchment.
Cabbage Tree Creek Recreational Waters Investigation
Final Summary Report