Stormwater pollution from urban areas
Natural areas generally have the capacity to absorb large amounts of rainfall before runoff occurs. The absorbed water is retained as groundwater or drains into breeks and rivers over time, maintaining stream flow. When such areas area developed for residential and industrial uses, large areas previously able to absorb water are covered by impervious footpaths, roads and roofs. As runoff (stormwater) drains into the river system, it picks up a variety of pollutants and litter from urban areas.
Sewerage system overflows
Most water that enters our homes leaves as sewage, including effluent from flushing toilets and the water that goes down the drain from washing clothes, showering, preparing food, etc. Sewerage can include food scraps, oils, grease, paints, pesticides, solvents and preservatives. Sewerage is managed by Sydney Water. Sometimes sewers can overflow, and affect a number of freshwater creeks, particularly in the upper and central Georges River. The overflows can result in algal blooms, weed infestations, and fish kills.
Impacts of developments
Development along the shore of the river can cause a number of problems. Wave action on the foreshores of Botany Bay; and the threat to remnant vegetation along foreshore areas are significant. Sediment and erosion due to runoff from urban subdivisions are also a major problem.
Marine vessels discharge into the river and Botany Bay (including ballast water) and cause erosion on the banks. Jet skis and speed boats increase rates of erosion of river banks.
There is inadequate management of leachate from existing and former landfill areas (rubbish dumps).
Rural and agricultural use
Agricultural runoff contains effluent from cattle and sheep, as well as any fertiliser or pesticides that have been used on the property. Traces of effluent contains high levels of nutrients such as phosphorous, and this can cause excessive growth of some aquatic weeds. Many native plants are not able to cope with the excess nutrients and are also killed. Pesticides can enter the food chain through bioaccumulation. The pesticides enter the waterway as runoff, are then absorbed by fish which are then eaten by other organisms. The poisons build up in larger animals causing death.
Land clearing destroys the habitat of native fauna and flora. The removal of vegetation exposes the soils to the actions of wind and water and makes it susceptible to erosion. Land clearing also reduces biodiversity. There are fewer species of plants, and as a result few species of animals will be attracted to the area. This can result in large scale pest infestations, and greater susceptibility to disease.
Eutrophication can occur as a result of fertilisers in runoff. Blue-green algae (the common name given to several species of algae) can create scums on the surface of rivers. The toxins produced by the algae can be poisonous to humans and other animals. As it decomposes the algae uses oxygen which results in fish kills.
Mining and Industrial Land use
In Botany Bay, the historic industrial discharges into the bay resulted in contamination of sediment on the bay floor. Industrial discharges can also result in fish kills, bioaccumulation or contamination of water and sediment.
Mining induced subsidence
Mining can result in the cracking of river beds, partial loss of surface flows, decline in water quality, release of gas reserves from underlying strata and increased rates of cliff-top collapse.
Removing sand or other sediments from the floor of a bay or river can alter the river morphology (flow), and disturb floor dwelling aquatic species.
Biodiversity (or biological diversity): The variety of all life forms, comprising genetic diversity within a species, species diversity and ecosystem diversity
Biota: all living things including micro-organisms, plant and animals.
Blue-Green algae: Microscopic bacteria. Under certain conditions (including high nutrients, warm still water, strong sunlight into the water) they can bloom into a dense and visible growth and become toxic.
Deoxygenated: With most or all oxygen removed. Water becomes deoxygenated (i.e. loses its dissolved oxygen) for a number of reasons including stagnation, eutrophication and rising temperatures.
De-snagging: The removal of fallen and dead branches from a watercourse.
Dissolved oxygen: Oxygen in the water (which may be used by aquatic animals)
Environmental flows: Flows of water, that are either protected or created for an environmental purpose.
Eutrophication: Excessive levels of aquatic plant growth (including algae) resulting from raised levels of nutrients and other factors.
Extraction: Water taken from rivers for off-stream use or for consumption.
Faecal coliform: A type of bacteria found in faecal material of humans and other mammals. Faecal coliforms themselves generally do not make people sick. High levels indicate that water is likely to contain other micro-organisms that make people sick.
Indicator (e.g. water quality, biological, ecological): Any physical, chemical or biological characteristic used as a measure of environmental quality.
Introduced species: Species of plants or animals that are not native to Australia (also referred to as exotic or alien species).
Natural flow regime: The likely pattern of flow before European settlement in Australia. In these guidelines, natural flow regime refers to the flow patterns without any regulation or extraction of water.
Nutrients: Nutritional substances. Unnaturally high levels of nutrients, such as in a river below a sewage treatment plant, can encourage abnormally fast and prolific growth of algae in the water, or weed growth in the bush.
Pathogen: Disease-causing organism.
Point-source pollution: A single, identifiable source of pollution, such as a drain from an industrial site or sewage treatment plant (as opposed to non point-source or diffuse-source pollution-coming from many small sources over a large area).
Potable water: Water fit for human consumption.
Raw water: Surface or groundwater that has received no treatment to make it suitable for drinking.
Salinity: The concentration of salts in soil or water, including sodium chloride (NaCl).
Suspended solids: The smaller, lighter material such as clay, silt and fine sand carried in suspension in water.
Turbidity: A measure of the amount of the light-scattering properties of water. It indicates how much silt, algae and other material is suspended in water. Highly turbid waters may look muddy, stain clothes, block irrigation sprays and pipes or harm aquatic organisms.
Where is the Georges River Catchment located?
The Georges River catchment covers approximately 960 square kilometres and about 800,000 people live in the catchment. The Georges River rises south of Appin near Campbelltown and flows downstream for 96 kilometres to enter Botany Bay at Sans Souci. A substantial part of the catchment is bushland contained in Heathcote National Park, the Holsworthy Army Base and on private and Crown land.
The upper catchment includes the upper reaches of the Woronora River and Dam and the Upper Georges River, O'Hares Creek and Prospect Reservoir. The lower catchment includes the urban areas of Campbelltown, Liverpool, Bankstown, Sutherland, Kogarah, Kurnell, Botany and areas around Botany Bay
There is a range of fieldwork techniques that can be used in studying catchment functioning. Some of these fieldwork techniques which relate specifically to the river include:
- water quality
- measuring changes in channel shape
- material carried in the stream
- biodiversity survey.
Below are links to videos from Georges Riverkeeper explaining some relevant types of fieldwork.
Below are duplicate activities for four different locations. These are intended as a single site fieldwork activity that you could fit into a single or double period if your school is located within walking distance of one of the fieldwork sites: Orphan School Creek, Chipping Norton Lake, Salt Pan Creek or Woronora River.
Deputy Principal at a Sydney high school. Coordinating author of the Geoactive text book series.