Eprapah Creek
Encyclopedia
Eprapah Creek is a sub-tropical stream located in Redland City close to Brisbane
in South East Queensland
, Australia
. The creek flows directly to the Moreton Bay
at Victoria Point
. It is basically 12.6 km long with about 3.8 km of estuarine zone. In the latter, the water depth is typically about 1 to 2 m mid-stream, the width is about 20–30 m and the tides are semi-diurnal with a range of about 2 m. The catchment (~ 39 km2 area) is mostly urban in the lower reaches and semi rural/rural residential in the upper reaches. It includes several conservation areas hosting endangered species: e.g., koalas, swamp wallabies, sea eagles.
QLD) over 30 years by Redland Shire Council, Environmental Protection Agency
(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 meters from the estuary in 2003-04.
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 turbulence
and water quality
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
of the water column was observed at all sampling locations, but the longitudinal distributions of dissolved oxygen and turbidity
showed a quasi-homogeneous estuarine system, in sharp contrasts with dry weather data sets. The salinity
data highlighted the advective
diffusion of the freshwater plume
. The observed saltwater intrusion
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.
Brisbane
Brisbane is the capital and most populous city in the Australian state of Queensland and the third most populous city in Australia. Brisbane's metropolitan area has a population of over 2 million, and the South East Queensland urban conurbation, centred around Brisbane, encompasses a population of...
in South East Queensland
South East Queensland
South East Queensland is a region of the state of Queensland in Australia, which contains approximately two-thirds of the state population...
, Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. The creek flows directly to the Moreton Bay
Moreton Bay
Moreton Bay is a bay on the eastern coast of Australia 45 km from Brisbane, Queensland. It is one of Queensland's most important coastal resources...
at Victoria Point
Victoria Point, Queensland
Victoria Point is a suburb located approximately south-east of Brisbane, the capital city of Queensland, Australia, in the Redland City local government area...
. It is basically 12.6 km long with about 3.8 km of estuarine zone. In the latter, the water depth is typically about 1 to 2 m mid-stream, the width is about 20–30 m and the tides are semi-diurnal with a range of about 2 m. The catchment (~ 39 km2 area) is mostly urban in the lower reaches and semi rural/rural residential in the upper reaches. It includes several conservation areas 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 PointVictoria Point, Queensland
Victoria Point is a suburb located approximately south-east of Brisbane, the capital city of Queensland, Australia, in the Redland City local government area...
QLD) over 30 years by Redland Shire Council, Environmental Protection Agency
Environmental Protection Agency (Queensland)
Queensland's Environmental Protection Agency was for some time a separate department of the Queensland Government, and, following 2009 State elections, became a part of the Government's larger Department of Environment and Resource Management.This part of the Department of Environment and...
(EPA) and local community groups. The creek was heavily polluted in 1998 by illegal discharges of tributyl-tin (TBT
Tributyltin
Tributyltin compounds are a group of compounds containing the 3Sn moiety, such as tributyltin hydride or tributyltin oxide. They are the main active ingredients in certain biocides used to control a broad spectrum of organisms...
) 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 meters 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 turbulenceTurbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
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 turbulence
Turbulence
In fluid dynamics, turbulence or turbulent flow is a flow regime characterized by chaotic and stochastic property changes. This includes low momentum diffusion, high momentum convection, and rapid variation of pressure and velocity in space and time...
and water quality
Water quality
Water quality is the physical, chemical and biological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which...
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
Mixture model
In statistics, a mixture model is a probabilistic model for representing the presence of sub-populations within an overall population, without requiring that an observed data-set should identify the sub-population to which an individual observation belongs...
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 (water)
Water stratification occurs when water masses with different properties - salinity , oxygenation , density , temperature - form layers that act as barriers to water mixing...
of the water column was observed at all sampling locations, but the longitudinal distributions of dissolved oxygen and turbidity
Turbidity
Turbidity is the cloudiness or haziness of a fluid caused by 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....
showed a quasi-homogeneous estuarine system, in sharp contrasts with dry weather data sets. The salinity
Salinity
Salinity is the saltiness or dissolved salt content of a body of water. It is a general term used to describe the levels of different salts such as sodium chloride, magnesium and calcium sulfates, and bicarbonates...
data highlighted the advective
Advection
Advection, in chemistry, engineering and earth sciences, is a transport mechanism of a substance, or a conserved property, by a fluid, due to the fluid's bulk motion in a particular direction. An example of advection is the transport of pollutants or silt in a river. The motion of the water carries...
diffusion of the freshwater plume
Plume (hydrodynamics)
In hydrodynamics, a plume is a column of one fluid or gas moving through another. Several effects control the motion of the fluid, including momentum, diffusion, and buoyancy...
. The observed saltwater intrusion
Saltwater intrusion
Saltwater intrusion is the movement of saline water into freshwater aquifers. Most often, it is caused by ground-water pumping from coastal wells, or from construction of navigation channels or oil field canals. The channels and canals provide conduits for salt water to be brought into fresh...
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.
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