Sydney Harbour

Since the early 1980's the water quality at beaches in Sydney has been an important issue with the community. The Harbourwatch program is currently responsible for the monitoring of the water quality to ensure the safety of the recreation users of Sydney Harbour.  Through the program daily reports are released for most popular swimming locations within the harbour. These reports state whether it is likely that the beach will be affected by high levels of pollution and are based on a logical set of rules (see table below). It is known that rainfall is responsible for flushing the pollution of the streets of Sydney into Sydney Harbour.

The aims of this project were to determine a new model that the Harbourwatch program could base their reports on. The predictive accuracy of the current model has been tested and found to have a predictive accuracy of between 70-90%. This at a first glance seems to be a very good model, but at closer inspection it was found that the current model gets the majority of its predictive accuracy from the fact that the base rates of bacteria within the harbour, i.e. the percentage of the time that the bacteria are low, is 70-90% depending on the location an bathymetry of the location.

It has been shown in Hose et al 2003(see thesis for complete reference), that the rainfall accounts for between 15-65% of the variability of the rainfall. So it appears that the current model is using all the available information from the rainfall. Ashbolt and Bruno 2003(see thesis for complete reference), found that a rising or high tide correlated with 70% of the high bacteria readings. Asbolt and Bruno 2003 also investigated the wind and number of sunlight hours affected the bacteria readings in times of low rainfall. These extra variables are yet to be incorporated into the model that I have developed, but it is hoped that in the near future, data will be available.

For more details of the Harbourwatch program you can read my thesis or visit the EPA's website at www.epa.nsw.gov.au/beach/ and follow the links to the Harbourwatch program or obtain a copy of the EPA's Annual State of the Beaches Report for a scientific Analysis and summary of the EPA's detail all the water quality programs which can be obtained through the above website.