Eprapah Creek (longitude 153.30º East, latitude -27.567º South) is a sub-tropical stream located in

Redland City Redland City, better known as the Redlands and formerly known as Redland Shire, is a Local government in Australia, local government area and a part of the Brisbane metropolitan area in South East Queensland. With a population of 156,863 in Jun ...

close to

Brisbane Brisbane ( ) is the capital and most populous city of the states and territories of Australia, Australian state of Queensland, and the list of cities in Australia by population, third-most populous city in Australia and Oceania, with a populati ...

South East Queensland South East Queensland (SEQ) is a bio-geographical, metropolitan, political and administrative region of the state of Queensland in Australia, with a population of approximately 3.8 million people out of the state's population of 5.1 million. T ...

, Australia. It rises on the north-eastern slopes of Mount Cotton and flows directly to the

Moreton Bay Moreton Bay is a bay located on the eastern coast of Australia from central Brisbane, Queensland. It is one of Queensland's most important coastal resources. The waters of Moreton Bay are a popular destination for recreational anglers and are ...

at Victoria Point. It is long with about of estuarine zone. In the latter, the water depth is typically about one to two m mid-stream, the width is about 20 to 30 m and the tides are semi-diurnal with a range of about two m. The catchment (~ 39 km2 area) is mostly urban in the lower reaches and semi rural/rural residential in the upper reaches. The creek includes several conservation areas such as

Eprapah Eprapah, the Charles S. Snow Scout Environment Training Centre, at Victoria Point, near Brisbane, Queensland, Australia, is a noted ecological area within Redland City. Owned and managed by the Scout Association of Australia, Queensland Branc ...

hosting endangered species, e.g. koalas, swamp wallabies, sea eagles.

Water quality

The water quality and ecology have been closely monitored at Eprapah Creek ( Victoria Point, Queensland) over thirty years by Redland Shire Council,

Environmental Protection Agency A biophysical environment is a biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environment can vary in scale f ...

(EPA) and local community groups. The creek was heavily polluted in 1998 by illegal discharges of tributyl-tin ( TBT) and chemical residues. Although the estuarine zone includes two environmental parks, there are some marinas and boat yards, and a major sewage plant discharge that affect the natural system. The upstream catchment has been adversely affected by large-scale poultry farms, wineries, land clearance and semi-urban development. The recent works included the constructions of new shopping centres and residential lots less than 500 metres from the estuary in 2003-04.

Turbulent mixing in Eprapah Creek estuary

Between 2003 and 2007, a series of field studies were performed in the estuarine zone of Eprapah Creek that is a typical small coastal plain type. The aim of these field studies was to investigate the

turbulence In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...

and turbulent mixing properties in the estuarine zone. During these studies, high frequency turbulence and physio-chemistry data were collected continuously over a relatively long duration (up to 50 h), and the findings have direct implications on the modelling of small estuaries. The studies showed that the response of the

and

water quality Water quality refers to the chemical, physical, and biological characteristics of water based on the standards of its usage. It is most frequently used by reference to a set of standards against which compliance, generally achieved through tr ...

properties were distinct under spring and neap tidal forcing and behaved differently in the middle and upper estuarine zones. The behaviour of turbulence properties to spring tidal forcing differed from that observed in larger estuaries and seemed unique to small estuarine systems. An investigation of several key turbulence parameters used in the modelling of estuarine mixing showed that many assumptions used in larger estuaries must be applied with caution or are simply untrue in small estuaries. For example, the assumption that the mixing coefficient parameters are constant over the tidal cycle in a small estuary is simply untrue. These distinctions between the turbulence and mixing properties in small and large estuarine systems highlight the need for the continued study of small estuaries, so this type of system can be properly understood. Like most small subtropical estuaries, Eprapah Creek is characterised by short-lived freshwater flushing, and basically no flow during the dry season. A recent field study highlighted the short-term impact of a rainstorm on a small subtropical estuary. The flushing appeared to be caused primarily by the rainfall runoff from the nearby shopping centres, parkings and roadways. In the estuary, the surface flows were dominated by the freshwater flushing including during the flood tide. Some strong vertical

stratification Stratification may refer to: Mathematics * Stratification (mathematics), any consistent assignment of numbers to predicate symbols * Data stratification in statistics Earth sciences * Stable and unstable stratification * Stratification, or st ...

of the water column was observed at all sampling locations, but the longitudinal distributions of

dissolved oxygen Oxygen saturation (symbol SO2) is a relative measure of the concentration of oxygen that is dissolved or carried in a given medium as a proportion of the maximal concentration that can be dissolved in that medium at the given temperature. It ca ...

and

turbidity Turbidity is the cloudiness or haziness of a fluid caused by large numbers of individual particles that are generally invisible to the naked eye, similar to smoke in air. The measurement of turbidity is a key test of water quality. Fluids can ...

showed a quasi-homogeneous estuarine system, in sharp contrasts with dry weather data sets. The

salinity Salinity () is the saltiness or amount of salt dissolved in a body of water, called saline water (see also soil salinity). It is usually measured in g/L or g/kg (grams of salt per liter/kilogram of water; the latter is dimensionless and equal ...

data highlighted the advective diffusion of the freshwater plume. The observed

saltwater intrusion Saltwater intrusion is the movement of saline water into freshwater aquifers, which can lead to groundwater quality degradation, including drinking water sources, and other consequences. Saltwater intrusion can naturally occur in coastal aquifers ...

data exhibited a dome-shaped intrusion curve, and the data followed an analytical model. The analytical solution provided a simple physical model of the salt dispersion in the alluvial estuary. It showed the significance of density-driven mixing in the upper estuary during wet weather conditions.

References

External links

A Hydraulic, Environmental and Ecological Assessment of a Sub-tropical Stream in Eastern Australia: Eprapah Creek
Victoria Point Qld on 4 April 2003 {{Rivers of Queensland Geography of Brisbane Redland City Rivers of Brisbane

Water quality

Turbulent mixing in Eprapah Creek estuary

See also

References

External links