The Onkaparinga River catchment is approximately 530 km2 and
includes a large portion of the southern Mount Lofty Ranges. The
monitoring site near Noarlunga is just above the upper limit of
tidal influence. See also other monitoring sites in this catchment
(Lenswood Creek, and Scott
Creek).
The site is in a conservation park; land use upstream is a mixture
of grazing, dairy farming, rural residential, horticulture and
viticulture with small patches of native vegetation. Elevated
turbidity and nutrient levels are the most likely water quality
problems. Stream
flow data for this site is available from the Department
of Water, Land and Biodiversity Conservation. >>
Map (2MB PDF)
The indicators that are measured in the Onkaparinga River are
nutrients (nitrogen and phosphorus), turbidity and salinity.
The concentrations of these indicators are used to classify the
water chemistry as being in good,
moderate or poor
condition, according to the needs of aquatic ecosystem protection.
Go here
to find out how we organise and classify the chemistry data.
Water chemistry classification for April to September 2006
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Indicator
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Classification
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Moderate
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Poor
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Good
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Good
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Good
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Nutrient concentrations (especially nitrogen) were elevated in
the lower reaches of the Onkaparinga River during this monitoring
period. Elevated nutrients are consistent with the site being
downstream from a large, intensive agricultural catchment area.
Fertilisers or animal wastes being washed off farms during storms
or effluent outfalls are considered to be the main sources of
nutrient contamination.
The salinity at this location varies widely from fresh through
to seawater concentrations. This is because tidal waters can extend
up as far as this location during dry periods and create a partially
estuarine environment. This is reflected by the mix of fresh and
marine vegetation that is seen in the area.
In view of the potential for estuarine waters to reach this far,
it is possible that the nitrogen concentration is increased at
this site by the SA Water sewage sludge lagoons that are considered
to impact the Onkaparinga Estuary.
Further monitoring is required to confirm that this is occurring.
There are several projects and programs which are designed to
improve water quality in the Onkaparinga River. These are being
coordinated through the Adelaide
and Mt Lofty Ranges Natural Resources Management Board.
>> Archived results
