Darwin Harbour in good health
Westra Van Holthe, Willem
Media Releases for 12th Assembly 2012 - 2016; Media Releases; ParliamentNT
Made available by via the Publications (Legal Deposit) Act 2004 (NT)
Oceans; Marine life
Northern Territory Government
Issued as a Media Release
Northern Territory Government
1 Summary of estuary and marine water quality grades 2014 1. Introduction Water quality monitoring has been undertaken in Darwin Harbour by the Department of Land Resource Management (and its predecessor organisations) since 1987 (Wrigley et al. 1990). The water quality of the harbour has been summarised annually in the form of a Report Card since 2009. The 2014 grades are shown in Figure 1, and presented with the grades for previous years in Table 1. This report supplements the 2014 Darwin Harbour Region Report Card by presenting supporting data and other information used to calculate the grades, as well as providing a more detailed analysis of Darwin Harbour water quality. The 2014 grades indicate that water quality was good to excellent. Deviations from excellent water quality, indicative of Water Quality Objective (WQO) non-compliance, are likely to be natural and an artefact of the grading methodology and WQOs. An exception though is Buffalo Creek which has consistently poor water quality due mainly to the combined effects of effluent discharged from the Leanyer-Sanderson wastewater treatment plant, and poor flushing of the creek. However although poor, the 2014 reporting year indicates a minor improvement to water quality in Buffalo Creek with improved conditions for the parameter of dissolved oxygen. Low over-night concentrations however probably occur. Myrmidon Creek, which receives effluent from the Palmerston wastewater treatment plant, has good water quality. The Shoal Bay and Myrmidon Creek had large variation in dissolved oxygen at times higher than water quality objectives or quite low, particularly in Myrmidon Creek within the influence of the licensed discharge. These oxygen levels however were not harmful and were not persistent. Their exceedence indicates the WQO needs to be revised to better take into account natural water quality variability, particularly in the case of Shoal Bay where no point sources influence water quality. 2. Darwin Harbour region The Darwin Harbour region is located in the wet-dry tropics of northern Australia and extends from Gunn Point in the east, to Charles Point in the west. The climate consists of two seasons: the wet and the dry. The wet season occurs between November and April and is characterised by heavy cloud cover, rain and humidity. The dry season occurs from May to October and is characterised by cooler temperatures, south east winds and little or no rain. The region has a population of over 130,000 people (ABS 2013) and covers over 3200 km (65% terrestrial and 35% coastal and marine at high tide). Darwin Harbour is a large, macro-tidal estuary with semi-diurnal tides (two high tides and two low tides) and characterised by strong tidal currents which result in extensive turbid plumes on outgoing tides.
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