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In the context of climate change, abatement is the reduction in greenhouse gas emissions or else the increase in removal of greenhouse gases from the atmosphere (e.g. by vegetation).

Absorption (water) 

The physical uptake of water and any material dissolved in it.

Absorption (electromagnetic radiation)

Absorption of electromagnetic radiation is the process by which the energy of the radiation (e.g. of photons of light) is taken up by matter (e.g. by the electrons of an atom). The electromagnetic energy is thereby transformed to other forms of energy (e.g. to heat or to electric potential).

For most substances, the amount of absorption varies with the wavelength of the incoming electromagnetic radiation. This can lead to the appearance of colour in substances that absorb some wavelengths but not others. For example, an object that absorbs blue, green and yellow light will appear red when illuminated by white light.


In Biology, an adaptation is defined as a particular inherited characteristic that enables an organism to survive in an environment.

In the context of climate change, an adaptation is an adjustment in natural or human social or economic systems that reduces the harm or exploits beneficial opportunities of climate change.


Describing the chemical characteristic of acid. Technically, a pH value below seven.

Acid sulphate soil

Includes actual acid sulphate soils and potential acid sulphate soils. Actual and potential acid sulphate soils are often found in the same soil profile, with actual acid sulphate soils generally overlying potential acid sulphate soil horizons.Actual acid sulphate soils: are soils containing highly acidic soil horizons or layers resulting from the aeration of soil materials that are rich in iron sulphides, primarily sulphide. This oxidation produces hydrogen ions in excess of the sediment's capacity to neutralise the acidity resulting in soils of pH of 4 or less when measured in dry season conditions. These soils can usually be identified by the presence of pale yellow mottles and coatings of jarosite. Potential acid sulphate soils: are soils which contain iron sulphides or sulphidic material which have not been exposed to air and oxidised. The field pH of these soils in their undisturbed state is pH 4 or more and may be neutral or slightly alkaline. However, they pose a considerable environmental risk when disturbed, as they will become severely acidic when exposed to air and oxidised.

Activated carbon

Particles or granules of carbon used in water treatment because of their high capacity to selectively remove certain trace and soluble materials. Usually obtained by heating a carbon source (such as wood).

Activated sludge process

This process involves using naturally occurring micro-organisms to feed on the organic material in the sewage. Activated sludge is a rich mixture of bacteria and minerals. The process is used in sewage treatment plants to break down organic matter and nitrogen compounds.


A process in which molecules are attracted to and retained on a surface (compare with absorption). In water treatment, the large surface area of activated carbon is used to remove low concentrations of contaminants.


The sideways movement of air in the lower atmosphere due to the differences in air pressure (commonly called wind). Process of transfer of air mass properties by the velocity field of the atmosphere


Exposure of material to air so that dissolved gases are removed; the process by which air is added to a substance
Aerobic As applied to water, refers to the presence of oxygen dissolved from the air (also see anaerobic).

Aerobic digestion 

Breakdown of organic matter in liquid by adding oxygen or air. This is a process used in sewage treatment.


An aerosol is a collection of airborne solid or liquid particles, with a typical size between 0.01 and 10 microns in diameter that is present in the atmosphere for at least several hours. Aerosols may be of either natural origin or arise from human activities e.g. smoke particles from burning wood. Aerosols may influence climate in several ways: directly through scattering and absorbing radiation, and indirectly by acting as condensation nuclei for clouds or modifying the optical properties and lifetime of clouds.

Air Pressure

The force per unit of area exerted by the atmosphere as a result of gravitational attraction exerted on the column of air lying above a particular point. Air pressure can be measured with a barometer. Air pressure drops logarithmically with height above the earth’s surface.


Comparatively simple chlorophyll-bearing plants, most of which are aquatic, and microscopic in size.

Algal bloom 

The occurrence of a high concentration of microscopic plant life, such as green or blue-green algae (cyanobacteria), in a river, lake and reservoir, usually as a result of increased nutrient content.


Describing the chemical characteristic that can neutralise acid. Technically, a pH value above seven.

Alien species 

See Introduced species.

Allocation reliability 

The long-term probability (over wet, dry and average years) of irrigators with 'normal security' water allocations being able to get a certain proportion of their nominal allocation by a specified date.


The volume of water a licence holder is entitled to extract during a year, subject to licence conditions and availability. Currently, only licence holders on regulated rivers supplied by irrigation dams have an allocation. (See also Off-allocation flows)

Alluvial aquifer/groundwater 

Groundwater (or sub-surface water) contained in the alluvial deposits near a river. It is usually directly connected to the river and therefore its level is closely related to river levels. Alluvial aquifers can be recharged directly from the river under high-flow conditions. Under low-flow conditions, alluvial aquifers can provide base flow in the river channel.

Ambient waters 

The ANZECC 2000 Guidelines define these as: "All surrounding waters, generally of largely natural occurrence". These include natural waterways, such as rivers, creeks, lagoons, wetlands and lakes (whether permanent, temporary, ephemeral or seasonal), groundwater and estuarine and marine waters. Ambient waterways can also include artificial water bodies such as reservoirs and lakes, where these have community value for aquatic ecosystems or for human uses. Environmental values of water (in the form of the NSW Water Quality Objectives) apply to these waters.


A gas produced from a mixture of nitrogen in the air and hydrogen from methane. One source of methane is sewage.


A stream that leaves the main stream and re-joins it further down.


Conditions where oxygen is lacking; organisms not requiring oxygen for respiration.

Anaerobic digestion 

Breakdown of organic matter under conditions of low air or oxygen supply.


An anomaly is a departure or deviation from the long-term average condition for some observed or measured variable. For example, if temperature were the variable being considered, and the temperature for December at Gosford in a particular year was 2 degrees Celsius lower than the long-term average for January then the anomaly would be -2 degrees Celsius.


Containing low levels of oxygen.


Caused or derived from human activities, as opposed to natural causes without human influences; for example the type of carbon dioxide emissions that result from humans burning fossil fuels in contrast to natural carbon dioxide emissions from cellular respiration by organisms in a wilderness environment.


Australian and New Zealand Environment and Conservation Council.


An underground layer of soil, rock or gravel able to hold and transmit water. Bores, spear-points and wells are used to obtain water from aquifers.


Agriculture and Resource Management Council of Australia and New Zealand.


The mixture of gases surrounding a planet; for example, the gaseous envelope surrounding the Earth. The Earth’s dry atmosphere consists of 78.1% nitrogen, 20.9% oxygen, together with a number of trace gases, such as argon, helium and greenhouse gases such as carbon dioxide (0.035% volume mixing ratio) and ozone. In addition, the atmosphere contains water vapour, the amount of which is highly variable but typically around 1%. The atmosphere also contains clouds and aerosols.

Australian drinking water guidelines 

The key Australian reference to drinking water quality published by the National Health and Medical Research Council (NHMRC) and the Agriculture and Resource Management Council of Australia and New Zealand (ARMCANZ).

Australian height datum (AHD) 

In 1971 the mean sea level for 1966-1968 was assigned the value of zero on the Australian Height Datum at thirty tide gauges around the coast of the Australian continent. The resulting datum surface, with minor modifications in two metropolitan areas, has been termed the Australian Height Datum (AHD) and was adopted by the National Mapping Council as the datum to which all vertical control for mapping is to be referred. Elevations quoted using this datum are normally followed with the acronym (AHD). See for further information.


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An area drained by a given stream and its tributaries.

Bank slumping 

The falling or slumping of a riverbank into the river. May occur due to removal of riparian vegetation, erosion or bank destabilisation. The term is used here to denote slumping resulting from a rapid decrease in river height, in which water drains more quickly from the river than it does from the banks, which then collapse under their own weight.


A backwater channel, often formed by a cut-off river bend, which forms a lagoon or pool when river levels fall.


A thousand million.


The process by which chemical substances are taken up by living things and retained and concentrated as they move up through the food chain.

Biochemical oxygen demand (BOD) 

The decrease in oxygen content in a sample of water that is brought about by the bacterial breakdown of organic matter in the water.


Capable of being broken down by natural chemical or biological processes into simple substances not harmful to the environment.

Biodiversity (biological diversity)

The variety of all life forms, comprising genetic diversity (within species), species diversity and ecosystem diversity.


Sewage sludge, organic residual remaining after domestic sewage treatment.


The part of the Earth system comprising all ecosystems and living organisms, in the atmosphere, on land (terrestrial biosphere) or in the oceans (marine biosphere), including derived dead organic matter, such as litter, soil organic matter and oceanic detritus.


All living things, including micro-organisms, plants and animals.


Water containing human excrement.

Blue-green algae (Cyanobacteria) 

Naturally occurring, microscopic, primitive photosynthetic 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 may become toxic.


A hole drilled to extract ground water.

Bulk water entitlements

A legal right under the Water Act (1989) to harvest and use water


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A group of bacteria that is a major cause of diarrhoeal illness.

Cap (water) 

A limit on the amount of water that may be diverted from the river for human uses, e.g. the Murray-Darling Basin Ministerial Council announced a cap on water use in the Murray-Darling Basin in 1995.

Carbon cycle

The flow of carbon (in various forms, e.g. as carbon dioxide) through the atmosphere, hydrosphere, biosphere and lithosphere.

Carbon dioxide

A gas (CO2) present in the atmosphere. It is an essential input in the process of photosynthesis by plants. It is also an important component of the gases contributing to the greenhouse effect.

Carbon dioxide equivalent

A standard measure of the amount of CO2 that would have the same global warming potential (GWP) as a particular quantity of a named greenhouse gas of interest, when measured over a defined timescale (generally, 100 years).


A catchment is an area of land surrounded by natural features, such as hills, from which all water flows to a common low point, such as a creek, lake, river or bay.

Catchment yield

The annual average volume of water run-off from a catchment

Cation exchange capacity (CEC)

The sum of exchangeable cations that a soil can absorb at a specific pH. It is usually expressed din centimoles of charge per kilogram of exchanges (cmolc/kg).


Thermodynamic scale of temperature. Temperature in degrees Celsius can be obtained from value in degrees Fahrenheit by the following formula: C = (F - 32) x 5/9

Channel capacity

The volume of water that can pass along the river channel at a certain point without spilling over the tops of the banks.

Chemical Symbol

The abbreviated name of a chemical element.  E.g. Carbon = C, Boron = B.  It is a way of writing out chemical names in short hand.  Most element names are derived from their Latin or Greek name so sometimes the chemical symbol does not relate to the English version of the name.  E.g. Sodium = Na (derived from the Latin name natrium)


Chloride in recycled waters comes from a variety of salts (including detergents) and is present as an ion (Cl-). In addition to its role in salinity, it can be toxic to plants, especially if applied directly to foliage and aquatic biota.


Use of chlorine as a means of disinfection.


A small amount of chlorine is used in some places to kill living things (pathogens) in the water supply that would make people sick if they drank them. However, it disappears (degrades) with time and the pathogens can regrow if the water is not covered.

Chlorofluorocarbons (CFCs) 

Chemicals that release chlorine atoms that destroy ozone high in the atmosphere.  When ultraviolet light waves (UV) strike CFC* (CFCl3) molecules in the upper atmosphere, a carbon-chlorine bond breaks, producing a chlorine (Cl) atom. The chlorine atom then reacts with an ozone (O3) molecule breaking it apart and so destroying the ozone. This forms an ordinary oxygen molecule(O2) and a chlorine monoxide (ClO) molecule. Then a free oxygen** atom breaks up the chlorine monoxide. The chlorine is free to repeat the process of destroying more ozone molecules. A single CFC molecule can destroy 100,000 ozone molecules.

* CFC - chlorofluorocarbon: it contains chlorine, fluorine and carbon atoms.
** UV radiation breaks oxygen molecules (O2) into single oxygen atoms


Circulation is the flow, or movement of a fluid (e.g. water or air) in or through a given area or volume. Circulation in the ocean refers to the usual flow of sea in currents. Circulation in the atmosphere refers to the movement of air masses.

Cirrus Cloud

High cloud, delicate, hair-like and feathery looking.


The part of the toilet that stores the water for flushing.


Climate is the historical memory of atmospheric conditions in defined regions and for defined durations (e.g.   decades, centuries, millennia); data for which come, for the most part, from records of hourly or daily measurements on defined variables (e.g. temperature, air pressure, wind speed), reduced by defined mathematical rules into simply understood summary statistics (e.g. means, maximums, minimums) and interpreted in terms of dynamic global models. By convention, a timeframe of about one human generation (about thirty years back) has been regarded as a reasonable basis for defining the climate of a region but climate does change and the word climate needs to take into account not just our knowledge of past atmospheric conditions but also reasonable expectations about the future.

Climate change

In this website, climate change is defined as the changes in climate that result from an alteration of the Earth’s atmospheric composition through human activity such as burning fossil fuels and land clearing. In this definition, climate change is distinguished from natural climate variability.

It should be noted that this definition is  similar to that of the Framework Convention on Climate Change (UNFCCC) and the Green Paper on the  Carbon Pollution Reduction Scheme released by the Australian Government in July 2008, but it differs from the more cautious definition used by the Intergovernmental Panel on Climate Change and by the Garnaut Climate Change Review 2008 which defines climate change as  "a change in the state of the climate that can be identified (e.g., by using statistical tests) by changes in the mean and/or the variability of its properties, and that persists for an extended period, typically decades or longer".

Climate system

The climate system is the complex system that determines our weather; it consists of the atmosphere, the hydrosphere (solid, liquid and gaseous), the lithosphere and the biosphere as well as the interactions between these components.

Climate variability

A naturally occurring phenomenon whereby a region’s climate will gradually change over time; to be contrasted with (human-induced) climate change.


Chemical used to coagulate • clump together • very fine particles into larger particles. Soluble salts of aluminium and ferric iron are the most commonly used coagulants in water treatment.


The clumping together of very fine particles into larger particles caused by the use of chemicals (coagulants). The chemicals neutralise the electrical charges of the fine particles and destabilise the particles. This clumping together makes it easier to separate the solids from the water by settling, skimming, draining, or filtering.

Coliform bacteria

Group of bacteria whose presence in drinking water can be used as an indicator for operational monitoring (Also referred to as thermotolerant coliforms, total coliforms).


Combustion or burning is a sequence of chemical reactions between a fuel and an oxidant in which heat energy is given out or both heat and light. The most common kind of combustion involves oxygen as the oxidant. The products of combustion involving oxygen are oxides of each element in the fuel. For example, when the gaseous fuel methane (CH4) is ignited in the presence of oxygen, heat and light are given out and two products form – carbon dioxide CO2, and water H2O (the oxide of hydrogen). 
The equation for this particular combustion reaction is:

CH4 + 2O2 ---> CO2 + 2H2O + “heat”

In reality, combustion processes are never perfect or complete. In smoke (flue gases) gases produced during the combustion of carbon (as in coal combustion) or carbon compounds (as in combustion of hydrocarbons, wood etc.), both unburned carbon (as soot) and carbon compounds (CO and others) will be present. Also, when air is the oxidant, some nitrogen will be oxidized to various nitrogen oxides (NOx).


Change from a gas to a liquid


Conduction is the transfer of energy through matter from particle to particle. For example, a spoon in a cup of hot soup becomes warmer because the heat from the soup is conducted along the spoon. Conduction is most effective in solids but it can also happen in fluids.


The place where two or more streams flow together.


Biological or chemical substance or entity, not normally present in a system, capable of producing an adverse effect in a biological system, seriously injuring structure or function

Contingency allowance

A volume of water reserved in a supply dam for release if and when needed for ecological and/or water quality reasons. For example, a release may be required to maintain water levels in a wetland to enable waterbirds to complete breeding, or to flush away an algal bloom.

Controlled streams

Streams where flow is usually controlled by upstream dams or diversion works, resulting in major changes to the natural flow patterns. These include regulated streams as defined in the NSW Water Act 1912, where water is released from storage to meet downstream irrigation needs.


Convection is the movement of molecules within fluids (e.g. liquids, gases) that results in the transfer of heat energy (and of matter) from one place to another within the fluid. Warm currents form and move mass and heat within the heated fluid. For example when water is heated in a pot, the warmer portions of the water are less dense and therefore, they rise. Meanwhile, the cooler portions of the water fall because they are denser.

Criteria (for water quality)

The ANZECC 2000 Guidelines define water quality criteria as “scientific data evaluated to derive the recommended quality of water for different uses. On this website, the term is used interchangeably with the term "Trigger value" and "guideline level".

Cumulonimbus cloud

Heavy, puffy, heaped, dark cloud of great vertical depth, often bringing rain. Some have a distinctive anvil shaped head


Clouds with a woolly, heaped appearance that often produce rain


Invertebrate animals that have segmented legs and hard shells, e.g. crabs, yabbies, prawns.


The cryosphere is the portion of the Earth’s surface where water is in solid form, including sea ice, lake ice, river ice, snow cover, glaciers, ice caps and ice sheets, and frozen ground (which includes permafrost).


Micro-organism commonly found in lakes and rivers that is highly resistant to disinfection. Cryptosporidium has caused several large outbreaks of gastrointestinal illness, with symptoms that include diarrhoea, nausea and stomach cramps. People with severely weakened immune systems (i.e. severely immunocompromised people) are likely to have more severe and more persistent symptoms than healthy individuals (adapted from United States Environmental Protection Agency).


Bacteria containing chlorophyll and phycobilins, commonly known as ‘blue-green algae’.



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Technically, the dam is the wall that holds the water in and the reservoir is the water. Commonly, though, the words are interchanged.


A Decile is one of the groups formed when a series of data values (e.g. a large set of temperature readings or rainfall recordings) is ranked and then divided into ten equal parts. When this is done: 

  • The 1st Decile cuts off the lowest 10% of data

  • The 5th Decile cuts off the lowest 50% of data 

  • The 9th Decile cuts off lowest 90% of data.

Demand management

An approach to reducing the consumption of water by reducing demand for it. Demand management includes educating people about how to save water, promoting the use of household and industrial appliances that use water more economically, such as dual-flush toilets, and putting a price on water that reminds people of its true value.


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.


The process of removing dissolved salts from seawater (or brackish water), so that it becomes suitable for drinking or other uses


The removal of fallen trees and dead branches from a watercourse.


A type of very small algae that can be used as an indicator of water quality.


A vessel or tank in which organic or chemical reactions take place under controlled conditions. Digesters are used in sewage treatment plants.

Direct potable use

Water that has been highly treated to make it suitable for human.  Drinking water use, and is conveyed directly from the wastewater treatment plant to the water supply system.

Direct reuse

The beneficial use of recycled water that has been contained during direct transfer from the wastewater treatment plant to the reuse site.


An oxidising agent (e.g. chlorine, chlorine dioxide, chloramines and ozone) that is added to water in any part of the treatment or distribution process and is intended to kill or inactivate pathogenic (disease-causing) micro-organisms.

Dissolved oxygen

Oxygen in the water (which may be used by aquatic animals).

Diversion weir

A small weir across a river or stream diverting water into a tunnel or pipeline.


NSW Department of Land and Water Conservation. Now named Department of Natural Resources (DNR).


Department of Natural Resources.


Volumes of water released or extracted from a pool or dam, thereby lowering the water level.

Drinking water

Water intended primarily for human consumption (but excluding bottled water, for the purposes of these guidelines).


Drought is an ‘acute water shortage’ (Australian Bureau of Meteorology) that results in part from a marked reduction in precipitation (e.g. a lack of rain, hail, snow) over an extended period of time. Although it would be useful to define drought in purely meteorological terms it is not a simple matter: the occurrence and characteristics of drought vary from one region to another and have different impacts on the environment and human purposes within each region. 

Dryland salinity

See Salinity.


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East Coast Low

An intense low-pressure system off the eastern coast of Australia especially in NSW, eastern Victoria and southern Queensland. Based on past records, east coast lows are more common in the autumn to winter months especially June, although they can occur at any time. On occasion, they can intensify to dangerous levels off the coast of NSW bringing cyclonic wind and rain conditions.


The study of the inter-relationships between living organisms and their environment 


Any system in which living organisms and their immediate physical, chemical and biological environment are interactive and interdependent. Examples are ponds, forests and wetlands. 


Treated sewage, the water that flows out of a sewage treatment plant. Effluent quality is assessed primarily through Biochemical Oxygen Demand (BOD), which measures the amount of oxygen required for the breakdown of the organic material contained in the effluent. Thus, effluent with very little organic matter will require very little oxygen and hence will have a low BOD.  The out-flow water or wastewater from any water processing system or device. 

Effluent creek

A creek that leaves a watercourse and does not return to it (the opposite of a tributary). ('Effluent' in this sense has nothing to do with pollution.)

Electrical conductivity (or EC units)

A measure of the ability of water to conduct an electric current between electrodes placed in the water; the value obtained relates to the nature and amount of salts present.

El Nino

Nowadays, the term El Niño refers to the extensive warming of the central and eastern Pacific that leads to a major shift in weather patterns across the Pacific. In Australia (particularly eastern Australia), El Niño events are associated with an increased probability of drier conditions 


Emission is the release of greenhouse gases into the atmosphere.

Endocrine disrupter

Substances that can stop the production or block the transmission of hormones in the body. 


Stands for El Niño-Southern Oscillation. 'El Niño' used here refers to the warming of the oceans in the equatorial eastern and central Pacific; Southern Oscillation is the changes in atmospheric pressure (and climate systems) associated with this warming (hence 'Southern Oscillation Index' to measure these changes). 'ENSO' is used colloquially to describe the whole suite of changes associated with an 'El Niño' event - to rainfall, oceans, atmospheric pressure etc 

Enhanced greenhouse effect

Enhanced greenhouse effect is an increase in the greenhouse effect with the potential to lead to climate change; brought about by human activities, whereby greenhouse gases such as carbon dioxide, methane, chlorofluorocarbons and nitrous oxide are being released into the atmosphere at a much greater rate than would occur through natural processes.

Enteric pathogen

Pathogen found in the gut. 


The Protection of the Environment Administration Act 1991 sets out a meaning of 'environment' as: 'Components of the earth, including: 
a. land, air and water 
b. any layer of the atmosphere 
c. any organic or inorganic matter and any living organism 
d. human-made or modified structures and areas, and includes interacting natural ecosystems that include components referred to in a-c.' 

Environmental allocation of recycled water

Allocation of recycled water directly to waterways or water bodies to benefit the environment. 

Environmental flow

Environmental allocation for surface water rivers, streams or creeks.  Flows, or characteristics of the flow pattern, that are either protected or created for an environmental purpose. 

Environmental flow release

Release from a water storage intended to maintain appropriate environmental conditions in a waterway 

Environmental impact statement (EIS)

A document which describes a proposed development or activity, predicts the possible or certain effects of the activity on the environment, and outlines safeguards to mitigate or control environmentally damaging effects. 

Environmental management system

The section of an overall management system which includes structure, planning activities, responsibilities, practices, procurements, processes and resources for developing, implementing, achieving, reviewing and maintaining an environmental policy. 

Environmental standard

A quantifiable characteristic of the environment against which environmental quality may be assessed. 

Environmental valuation

Technique employed to estimate the worth of an environmental resource from the perspective of society as a whole in the absence of prices. 

Environmental value

The ANZECC 2000 Guidelines define environmental values as: 'particular values or uses of the environment that are important for a healthy ecosystem or for public benefit, welfare, safety or health and that require protection from the effects of pollution, waste discharges and deposits. Several environmental values may be designated for a specific water body. 


Temporary or intermittent, for instance a creek or wetland that dries up periodically. 

Escherichia (E.) coli

A type of faecal coliform bacteria (see below) which is found in large numbers in the faeces of humans and other mammals. It serves as a reliable indicator of recent faecal contamination of water. 

Escherichia coli

Bacterium found in the gut, used as an indicator of faecal contamination of water. 


Concerning an estuary, the part of an inlet or waterway that meets the sea and is subject to tidal movements. The water is usually brackish - a mixture of salt and fresh water. 


The part of a river in which water levels are affected by sea tides, and where fresh water and salt water mix. 

Euphotic depth/zone

The lit region of a body of surface water. This extends from the surface down to the deepest level at which there is sufficient light for photosynthesis to occur. 


Degradation of water quality due to enrichment by nutrients such as nitrogen and phosphorus, resulting in excessive algal growth and decay and often low dissolved oxygen in the water. 


Change from a liquid to a gas.  The process by which water changes from liquid to gas or vapour and rises, forming clouds. This happens when the temperature increases over large masses of water, such as lakes and oceans. 


Evapotranspiration is the combined process of transpiration from vegetation and evaporation from the ground in which it is growing.

Exchangeable sodium percentage (ESP)

The proportion of sodium adsorbed on soil clay mineral surface, as a percentage of total cation exchange capacity (used as a measure of soil sodicity). 


Water taken from rivers for off-stream use or for consumption. 


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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.

Fish ladder or fish-way

A structure designed to enable fish to move over a physical barrier (dam or weir) in a waterway. 


The gathering together of fine particles in water by gentle mixing after the addition of coagulant chemicals to form larger particles. 


A flood occurs when water inundates (covers) land which is normally dry.

Flood channel

A natural channel in a floodplain, which carries flowing water only during a flood. 

Flood mitigation

Levee banks and other structures which hold back water in time of flood, reducing (mitigating) damage to property. 


Flat land beside a river that is inundated when the river overflows its banks during a flood. 

Flood runners

Channels that run with water only during floods and very high flows. 


Flows that are high enough at their peak to overrun river banks or cause flow through high-level anabranches, floodrunners or to wetlands. 


The addition of a chemical to increase the concentration of fluoride ions in drinking water to a predetermined optimum limit to reduce the incidence of tooth decay in children. 

Flow regime

The pattern of flow in a river which can be described in terms of quantity, frequency, duration and seasonal nature of water flows. 


A dense mass of small water droplets or particles in the lower atmosphere 

Fossil fuel

A fossil fuel is a combustible carbon-containing material obtained from geological deposits formed in the Earth’s crust during times past from the fossil remains of plants and animals that lived on Earth up to 300 million years ago. Fossil fuels include hydrocarbons such as liquid petroleum and natural gas as well as non-volatile materials composed mainly of carbon such as anthracite coal and brown coal. These fuels can be burned in the presence of oxygen to transform their chemical potential energy into active heat (and light) energy.


Flows that produce a substantial rise in river height for a short period, but which do not overrun the river banks or inundate areas of land. 


A weather front is the boundary zone between two distinct air masses with different features. 


Deposit of soft white ice crystals or frozen dew drops on objects near the ground; formed when surface temperature falls below freezing point 


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General circulation model

A general circulation model (GCM) is a computer program that mimics the large-scale motions of the atmosphere and ocean that result from the differential heating on the rotating Earth. A GCM simulates the behaviour of the real atmosphere and oceans by incorporating our understanding of physical climate processes into a set of mathematical equations which are used to calculate the future evolution of the climate system from some initial conditions. The key equations are those relating to the conservation of mass, momentum and energy in the atmosphere and ocean. The equations are solved at a large number of individual points on a three dimensional grid covering the world or by equivalent methods.

Giardia lamblia 

A protozoan frequently found in rivers and lakes. If water containing infectious cysts of Giardia is ingested, the protozoan can cause a severe gastrointestinal disease called giardiasis. 


A gigalitre is one thousand million (1,000,000,000 or 109) litres. 


A large, slow moving river of ice that is formed from compacted layers of snow.  They are able to sculpt mountains and carve out valleys.  Glacial ice advances and retreats in response to climate patterns.

Global Climate Observing System

The Global Climate Observing System (GCOS) is an international program established to ensure that the observations required to address global climate issues are obtained according to international standards and are made available to all potential users. It is intended to be a long-term system capable of providing the data required for monitoring the climate system, detecting and attributing climate change, assessing the impacts of climate variability and change, and supporting research toward the improved understanding, modelling and prediction of the climate system.

Global Mean Temperature

The global mean temperature is an estimate of the Earth's surface temperature; it is the area-weighted global average of (i) the sea-surface temperature over the oceans (i.e. the subsurface bulk temperature in the first few meters of the ocean), and (ii) the surface-air temperature over land at 1.5 m above the ground. The land-surface atmospheric temperature record comprises the combined results from thousands of thermometers measuring temperatures in every country around the world. Sea surface temperatures are determined mainly from ship-board measurements. The resulting data is statistically collated according to well-defined procedures by two leading institutions, the NASA Goddard Institute for Space Studies (GISS) in the U.S. (1880 until present) and the Climatic Research Unit (CRU) at the University of East Anglia in Britain (1850 until present).

Global warming

An increase in the average temperature of the Earth's surface. Global warming is one of the consequences of the enhanced greenhouse effect.

Great Artesian Basin

A vast, very deep store of underground water below much of the drier regions of eastern Australia. 

Greenhouse effect

The trapping of heat by naturally occurring greenhouse gases (such as water vapour, carbon dioxide, nitrous oxide, methane ) that keeps the earth about 30°C warmer than if these gases did not exist.

When the sun's energy reaches the earth some of it is reflected back to space and the rest is absorbed. The absorbed energy warms the earth's surface which then emits heat energy back toward space as longwave radiation. This outgoing longwave radiation is partially trapped by the greenhouse gases which then radiate the energy in all directions, warming the earth's surface and atmosphere.

Greenhouse gases effectively absorb infrared radiation emitted by the earth’s surface, by the atmosphere itself due to the same gases, and by clouds. Atmospheric radiation is emitted to all sides, including downward to the earth’s surface. Thus greenhouse gases trap heat within the surface-troposphere system.

Greenhouse gases

These are gases that cause the greenhouse effect. The major GHGs are carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), hydrofluorocarbons (HFCs), perfluorocarbons (PFCs), and sulphur hexafluoride (SF6). 

Greenhouse gases are both natural and anthropogenic (i.e. caused by human activity). They absorb and emit radiation at specific wavelengths within the spectrum of infrared radiation emitted by the earth’s surface, the atmosphere and clouds. Water vapour (H2O), carbon dioxide (CO2), nitrous oxide (N2O), methane (CH4) and ozone (O3) are the primary greenhouse gases in the earth’s atmosphere. Moreover there are a number of entirely human-made greenhouse gases in the atmosphere, such as certain halocarbons, and sulphur hexafluoride (SF6).


Wastewater from the hand basin, shower, bath, spa bath, washing machine, laundry tub, kitchen sink and dishwasher. Water from the kitchen is generally too high in grease and oil to be reused successfully without significant treatment. 


Water contained in rocks or subsoil.  Underground water filling the voids in rocks; water in the zone of saturation in the earth's crust.


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The type of environment in which a given animal or plant lives and grows, including physical and biological conditions. 


Precipitation (falling) of particles of ice (hailstones). Usually spheroid, conical or irregular in form and with a diameter varying generally between 5 and 50 millimetres.  Hail falls from clouds either separately or collected into irregular lumps. 


The time it takes for half the atoms in a sample of radioactive material to break down into a non-radioactive element. Half-lives vary significantly, from a few days for some elements to millions of years for others. Half-life measurement is important when considering the long-term storage or disposal of radioactive waste. 


A hard, generally impermeable surface placed over soil-e.g. concrete or bitumen. 

Hard water

Water that is difficult to make soap suds in because it contains calcium and magnesium salts. 


The small streams on the higher ground of a catchment, which flow into a river. 

Heavy metals

Metallic elements with high atomic weights, e.g. mercury, chromium, cadmium, arsenic and lead. They can cause damage to living organisms at very low concentrations and tend to accumulate in the food chain. 

Heat island

An area within an urban area characterized by temperatures higher than those of the surrounding area because of the absorption of solar energy by man-made materials like asphalt.

Heat radiation

Heat radiation (thermal radiation) is emitted by the Earth’s surface, the atmosphere and the clouds. It is also known as terrestrial or longwave radiation, and is to be distinguished from the near-infrared radiation that is part of the solar spectrum. Infrared radiation, in general, has a distinctive range of wavelengths (spectrum) longer than the wavelength of the red colour in the visible part of the spectrum. The spectrum of thermal infrared radiation is practically distinct from that of shortwave or solar radiation because of the difference in temperature between the Sun and the Earth-atmosphere system.

High flows

Higher than normal flows, which occupy much of the river channel or which overrun banks. In these guidelines, high flows in the middle and lower reaches of rivers are those that are greater than the level that long-term records indicate would naturally be exceeded 30% of the time (i.e. the 30th percentile). 

High-security water use

Licensed entitlement to a more secure water supply than under normal-security licences, e.g. for horticulture and town water supplies. 


Healthy Rivers Commission now disbanded see NRC.


A measure of water vapour in the air.

Hydrographic shape

Describes the flow pattern of water, for example, after a short storm or runoff from prolonged rain. 


The study of the distribution and movement of water.  An earth science concerned with the occurrence, distribution and circulation of waters on and under the earth's surface, both in time and space, their biological, chemical and physical properties, their reaction with the environment, including their relation to living beings. 


In this website, the hydrosphere refers to the totality of the Earth’s water  - comprising surface and subterranean water, such as oceans, seas, rivers, fresh water lakes, underground water; the water vapour of the atmosphere; and the solid water (ice) of the cryosphere. (Note: According to some other definitions, the hydrosphere is confined to the earth's liquid water component and excludes the  water vapour of the atmosphere and the solid water of the cryosphere).


Chemical compounds containing available chlorine; used for disinfection. They are available as liquids (bleach) or solids (powder, granules and pellets). 


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An ice cap is a dome-shaped ice mass that covers less than 50,000 km² of land area (usually covering a highland area). Masses of ice covering more than 50 000 km² are ice sheets.  Ice caps are not constrained by topographical features (i.e., they will lie over the top of mountains) but their dome is usually centred around the highest point. 

Indicator (e.g. water quality, biological, ecological)

Any physical, chemical or biological characteristic used as a measure of environmental quality.  
Infiltration The movement of water through soil or other porous material; the entry of stormwater into the sewerage system through faulty pipes. 

Industrial age

A period of rapid industrial growth with far-reaching social and economic consequences, beginning in Britain during the second half of the eighteenth century and spreading to Europe and later to other countries including the United States. The invention of the steam engine was an important trigger of this development. The industrial revolution marks the beginning of a strong increase in the use of fossil fuels and emission of carbon dioxide originating from their combustion.

Infrared radiation

Infrared (IR) radiation is electromagnetic radiation whose wavelength is longer than that of visible light, but shorter than that of microwaves. The name means "below red" (from the Latin infra, "below"), red being the colour of visible light with the longest wavelength. Infrared radiation has wavelengths between about 750 nm and 1 mm.

Far-infrared radiation is that portion of the infrared spectrum known as terrestrial radiation or longwave radiation because it is at wavelengths typical of the radiation emitted by the Earth’s surface and clouds. It is to be distinguished from the near-infrared radiation that is part of the solar spectrum.


Services and equipment needed to support urban communities, generally including water supply, stormwater and waste treatment facilities, electricity, telephones, roads and community services required for residential, commercial and industrial activities. 

Inorganic contaminants

Mineral-based compounds such as metals, nitrates, and asbestos. These contaminants are naturally-occurring in some water, but can also get into water through farming, chemical manufacturing, and other human activities. There are legal limits on some inorganic contaminants. 

Introduced species

Species of plants or animals that are not native to Australia (also referred to as exotic or alien species). 


Animals without backbones, including worms, insects, shrimps, crabs, snails, shellfish and zooplankton. Macro-invertebrates are large enough to be seen without the aid of magnification; micro-invertebrates need to be viewed through a microscope. 


An atom or group of atoms which has gained or lost electrons and carries an electric charge. 


The application of water to cultivated land or open space to promote the growth of vegetation  
Irrigation salinity See Salinity.


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Kyoto Protocol

An international treaty negotiated under the auspices of the UNFCCC. It entered into force in 2005. Among other things, the Protocol set binding targets for the reduction of greenhouse gas emissions by individual developed countries to be met within the first commitment period of 2008–12. The working agreement of the signatories to the Kyoto Protocol committed developed countries to reduce their collective emissions of six greenhouse gases by at least 5 per cent of 1990 levels by 2012. The Kyoto agreement became legally binding on 16 February 2005 when 132 signatory countries agreed to strive to decrease carbon dioxide emissions.


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La Nina

The extensive cooling of the central and eastern Pacific Ocean. In Australia (particularly eastern Australia), La Niña events are associated with increased probability of wetter conditions.  Changes to the atmosphere and ocean circulation during La Niña events include:
· Cooler than normal ocean temperatures across the central and eastern tropical Pacific Ocean. 
· Increased convection or cloudiness over tropical Australia, Papua New-Guinea, and Indonesia. 
· Stronger than normal (easterly) trade winds across the Pacific Ocean (but not necessarily in the Australian region). 
· High (positive) values of the SOI (Southern Oscillation Index).

A La Niña event is sometimes called an anti-ENSO (anti-El Niño-Southern Oscillation) event 

Latent heat

Latent heat is the amount of energy in the form of heat released or absorbed by a substance during a change of phase (i.e. solid, liquid, or gas).

Latent heat (literally, hidden heat) is taken up and stored when a substance changes state from a solid to a liquid, from a liquid to a gas, or from a solid directly to a gas or - in the reverse direction - is given up when a gas condenses to a liquid or a liquid freezes to become a solid. Latent heat is gained by water molecules when water evaporates. The heat added during evaporation is used to break hydrogen bonds between water molecules and does not raise the temperature of the water body. The heat then is "hidden" or stored in the water molecule until it is released during condensation. At that point, the heat is converted into sensible heat (literally, heat that can be felt).

Latent heat released during condensation is an important source of energy to drive atmospheric systems like hurricanes and cumulus clouds.


The process by which soluble materials in soil, such as salts, nutrients, pesticide chemicals or contaminants, are washed into a lower layer of soil or are dissolved and carried away by water. 


A constructed embankment to prevent a river overflowing. 


The upper layer of the solid Earth, both continental and oceanic, which comprises all crustal rocks and the uppermost cooler part of the mantle.

Low flows

Flows that occupy only a small portion of the river channel. Low flows would normally occur when there is little contribution to the river from rainfall events. For the purposes of the river flow objectives, the low flow is defined as the flow which occurs less than 20% of the total time that the river is flowing. 


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A plant large enough to be seen without the aid of a microscope. 


A mean or average value over a stated period is the arithmetic mean. This is obtained by totalling the individual values and then dividing this total by the number of values. The mean of an element for a particular month is obtained by totalling all the values of that element for that month over the period of record and dividing by the number of values. 


The median is the middle value in a data set ranked from lowest to highest. 


10 to the power of 6, or 1 million. 

Megalitre (ML)

One million litres (one Olympic swimming pool is approximately 2 ML).


Relates to the science of meteorology - the science that studies and measures the state and changing behaviour of the atmosphere, especially weather and weather conditions. 


A gaseous by-product of the breakdown of molecules that contain carbon. Most organisms, including humans, produce it. 

Microbiological quality 

In these guidelines, refers to the quality of water in terms of the level of disease-causing organisms it contains. 


Water under pressure passes into pipes constructed of filter membranes with tiny pores too small to admit suspended solids and some pathogens. 


Organism too small to be visible to the naked eye. Bacteria, viruses, protozoa, and some fungi and algae are micro-organisms. 

Milankovich cycles

Milankovich cycles are cycles in the earth's orbit that influence the amount of solar radiation striking different parts of the earth at different times of year. They are named after a Serbian mathematician, Milutin Milankovitch, who explained how these orbital cycles cause the advance and retreat of the polar ice caps.


In the context of climate change, mitigation is human intervention to reduce the emission of greenhouse gases caused by human activity or to increase the uptake of these gases by sinks (e.g. uptake of CO2by forests and oceans).


A model is a simplified representation of a complex phenomenon based on our human understanding (e.g. theory) of its main features or workings abstracted for the human purposes of projecting how the phenomenon might appear or behave in some scenario. A model can be concrete in form (e.g. an architect’s scale model of a building based on a design blueprint for the eventual construction of the real building) or abstract (e.g. a set of interlocking mathematical equations based on laws and theories of nature and leading to predictions about hypothesised events). Confidence in such models for predicting the future depends on their demonstrated ability to represent the major features of the past and present.

Multi-level off-take

An off-take structure within a dam, which can take water from various depths, rather than just one. For instance, if the off-take is only at the bottom of the dam, releases of water may be cold, deoxygenated and nutrient-rich. A multi-level off-take allows releases to be made from upper layers where water quality is often better. 


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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. 


National Health and Medical Research Council. 


The oxidation of ammonia nitrogen to nitrate nitrogen in wastewater by biological means. 


The chemical element with atomic number 7. As a diatomic molecule it is a colourless and odourless gas at room temperatures, and comprises 78% of the Earth's normal atmosphere. 

Nitrogen is an essential element in the chemisty of living things, especially abundant in proteins and nucleic acids. Though important to plant nutrition, nitrogenous ions and compounds can cause problems of eutrophication in waterways such as lakes, rivers and estuaries. They can also contaminate ground water.  Nitrogenous nutrients are sometimes found in high concentrations in recycled waters originating from human and domestic wastes. 

Non-point source pollution

See Point-source pollution. 


Natural Resources Commission - established in 2003 to provide independent advice to the NSW Government on natural resource management issues.


National River Health Program. 


Nephelometric turbidity unit (a unit of measurement for turbidity). 

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. 


National Water Quality Management Strategy. A joint initiative of the state and federal governments, to pursue sustainable use of the nation's water resources by protecting and enhancing their quality while maintaining economic and social development. 


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Ocean outfall

A site where liquid, usually treated effluent from a sewage treatment plant, is discharged through a pipe into the ocean. 

Off-allocation flows

Water that has not been released from storage, but comes from dam spills and/or inflows from tributaries below the dam. Licence holders are permitted to extract water from these flows but water so extracted is not debited against their allocation. 

Off-allocation period

When access to flows (dam spills or tributary inflows downstream of dams) is permitted by licence holders without debit against their allocated volume. The DLWC announces the start of an off-allocation period, usually when flows are greater than are needed to meet on-allocation orders. 

Off-take structure

A structure or point of diversion for water transfer. For instance, water is released from a dam via an off-take structure (see also multi-level off-take). 


Water ordered by a licence holder and which will be debited against their actual allocation. 


Substances that come from animal or plant sources. Organic substances always contain carbon. 


The passage of a liquid from a weak solution to a more concentrated solution across a semipermeable membrane. The membrane allows the passage of the solvent (water) but not the dissolved solids (solutes). This process tends to equalize the conditions on either side of the membrane. 


The addition of oxygen, removal of hydrogen, or removal of electrons from an element or compound. It is the opposite of reduction. In the environment, organic matter is oxidized to more stable substances. 


The application of ozone to water for disinfection or for taste and odour control. 


One of the several gases that make up the Earth's atmosphere. It is the triatomic* form of oxygen and makes up approximately one part in three million of all of the gases in the atmosphere. If all the ozone contained in the atmosphere from the ground level up to a height of 60 km could be assembled at the earth's surface, it would comprise a layer of gas only about 3 millimetres thick, and weigh some 3000 million tonnes. Ozone is toxic at high concentrations because it reacts strongly with other molecules.

* Each ozone molecule is made up of three oxygen atoms 

Ozone layer

The ozone layer is a band of the stratosphere in which the concentration of ozone (the O3 molecule of oxygen) is greatest. The layer extends from about 12 to 40 km above ground level. The ozone concentration reaches a maximum between about 20 and 25 km.


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A disease-causing organism (e.g. bacteria, viruses and protozoa). 


In these guidelines, usually refers to flow duration curves. The horizontal scale of the graph is divided from 0 to 100 percentiles (or per cent of time), while the vertical scale is flow rate (often in ML/day). For example, when looking at flow rates, the 90th percentile is the daily rate that is exceeded on 90% of days at a specific location. If the 90th percentile is 13 ML/day, then the stream flow would be higher than 13 ML/day for 329 days per year, and lower for 36 days per year.  
pH An expression of the intensity of the basic or acid condition of a liquid. Natural waters usually have a pH between 6.5 and 8.5. 


An important nutrient found in high concentrations in recycled waters, originating principally from detergents but also from other domestic wastes. A useful plant nutrient that can also cause off-site problems of eutrophication in water bodies. 


A process in which organisms, with the aid of chlorophyll (green plant pigment), convert carbon dioxide and inorganic substances into oxygen and additional plant material, using sunlight for energy. All green plants grow by this process. 

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). 


Substance that damages the quality of the environment. 


Pollution is anything that would harm us and other living things in an environment. Water pollution generally includes chemicals, bacteria and viruses, other micro-organisms and rubbish. These are called pollutants. 

Potable (drinking) water

Water suitable on the basis of both health and aesthetic considerations for drinking or culinary purposes.  Water fit for human consumption. 

Precautionary principle

The principle that the lack of scientific certainty should not be a reason to postpone preventive measures to avert threats of serious or irreversible environmental damage. 


The general term for rainfall, snowfall and other forms of frozen or liquid water falling from clouds. It occurs when the atmosphere becomes saturated with water vapour and the water condenses and falls out of solution (i.e. precipitates). Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapour to the air. Precipitation that reaches the surface of the Earth can occur in many different forms, including rain, freezing rain, drizzle, snow, ice pellets, and hail.


A prediction is a statement or claim that a particular event will occur in the future with a calculated degree of likelihood based on past experience of similar events. Predictions are often expressed in probabilistic terms.

Primary sewage treatment

The first major stage of treatment of sewage, usually involving the removal of solids.


Relating to probability.  The behaviour of a probabilistic system cannot be predicted exactly but the likelihood of certain events/outcomes occurring or not can be determined/calculated.


In the context of climate change, a projection is a description of the potential response of the climate system to emission or concentration scenarios of greenhouse gases and aerosols, or other radiative forcing scenarios, often based upon simulations by climate models. The distinction between projections and predictions is very important in that the climate projections are dependent, among other things, on the assumptions that are made in respect of the future emissions of greenhouse gases and other forcing agents. These scenarios concern future socio-economic and technological developments etc, that may or may not be realised, and are therefore subject to substantial uncertainty. Since there is no way of determining what these will be (they will depend on future human actions) it is impossible, even with the best climate models, to actually predict the future climate.


Parts of a plant (such as seeds, roots or stems) from which new plants can germinate. 


Microscopic animals, sometimes pathogenic in humans. They include Giardia and Cryptosporidium, which live in water. 

Pulsing supply

A strategy to reintroduce variability to releases of water from dams; introducing pulses of flow below dams allows a more natural flow pattern.


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Quality assurance (QA)

All the planned and systematic activities implemented within the quality system, and demonstrated as needed, to provide adequate confidence that an entity will fulfil requirements for quality (AS/NZS ISO 8402:1994). 


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Radiation (electromagnetic) 

Radiation is the transfer of energy (e.g. heat, light) through space or a transparent medium in the form of electromagnetic waves. Sunlight is a form of radiation that is radiated through the vacuum of space and then through our atmosphere to reach the opaque ground surface of our planet.

Ramsar Wetlands

Wetlands of international importance listed under the Ramsar Convention. To be put on the register, a wetland has to fulfil certain criteria-such as being important to the survival of migratory birds or endangered plant and animal species. 

Raw water

Surface or groundwater that has received no treatment to make it suitable for drinking. 

Recharge in-take bed

Areas like sandstone hills or gravely river banks, which prolonged rainfall or high flows, seep through to refill an underground water body. 


Water that infiltrates through the soil surface to the watertable. 

Reclaimed water

A term often used to define water recycled from treated sewage. 

Recycled water

Water taken from any waste (effluent) stream and treated to a level suitable for further use, where it is used safely and sustainably for beneficial purposes.  This is a general term that can include reclaimed water. 

Reference climate station

A climatological station, the data of which are intended for the purpose of determining climatic trends. This requires long periods (not less than thirty years) of homogeneous records, where human-influenced environmental changes have been and/or are expected to remain at a minimum. Ideally the records should be of sufficient length to enable the identification of secular (lasting for ages) changes of climate.


Reflection is the bouncing back of a wave when it hits a boundary between two substances at a certain angle.

A wave front changes direction (refraction) at an interface between two different media. In the case of reflection, the wave front changes direction so radically that it returns back into the medium from which it originated. A common example is the reflection of light by a mirror. Reflection of light may be specular (that is, mirror-like) or diffuse (that is, not retaining the image, only the energy) depending on the nature of the interface.


A river or creek where water is released from storage to meet diversion requirements downstream. 


A structure used to control the flow of water, for example, diverting water away from the main channel down an effluent creek. 

Retarding basin

Retarding basins are used where hard surfaces in urban areas lead to rapid build up of stormwater. This flow can be temporarily stored in a basin and released more slowly, preventing flooding downstream. 

Reverse osmosis

An advanced method of wastewater treatment which relies on a semi permeable membrane to separate water from its impurities. 


A shallow area of the river in which water flows rapidly over stones or gravel. 

Riparian zone

The area along the bank of a river or a stream, which often has water-dependent vegetation. 

Risk assessment

The overall process of using available information to predict how often hazards or specified events may occur (likelihood) and the magnitude of their consequences (adapted from AS/NZS 4360:1999). 

River alluvium

Material deposited by a flood. 


That part of rainfall which flows from a catchment area into streams, lakes, rivers or reservoirs 


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'Dissolved oxygen sag'-a section of the river where dissolved oxygen levels are depleted, often below a pollution source. 

Saline Salty

The salinity levels in water affect its usefulness for a range of purposes, and its harmfulness to the environment. 


The presence of soluble salts in soils or waters. Electrical conductivity and total dissolved salts are measures of salinity.  The concentration of salts in soil or water, including sodium chloride (NaCl). Dryland salinity is caused by clearing deep-rooted vegetation on areas of saline watertables. The uptake of water by plants is reduced, allowing the watertable with soluble salts to rise, killing plants and creating bare areas prone to erosion. Irrigation salinity occurs when irrigation raises the watertable, bringing high concentration of salt within root zones of plants, killing and stunting vegetation. It results from applying more water than can be used by the crop and by clearing of deep-rooted vegetation such as trees. Urban salinity is when rising watertables cause damage to infrastructure such as roads, underground pipes, houses and gardens. Urban salinity has been identified in NSW in 26 inland towns and in western Sydney. 


An outline of a supposed series of future events based on reasoning from present data and from what we already know about past trends of events. A climate scenario is a plausible and often simplified description of how the future climate may develop, based on knowledge of initial conditions and a set of assumptions about driving forces and key relationships. Scenarios may be derived from model projections, but are often based on additional information from other sources, sometimes combined with a narrative storyline.


In Australia, the seasons are defined by grouping the calendar months in the following way:
· Spring - the three transition months September, October and November. 
· Summer - the three hottest months December, January and February. 
· Autumn - the transition months March, April and May. 
· Winter - the three coldest months June, July and August. 
These definitions reflect the lag in heating and cooling as the sun appears to move southward and northward across the equator. They are also useful for compiling and presenting climate-based statistics on time scales such as months and seasons 

Secondary effluent

The liquid portion of wastewater leaving secondary treatment. 

Secondary sewage treatment

Generally, a level of treatment that removes 85 per cent of BOD and suspended solids, generally by biological or chemical treatment processes. Secondary effluent generally has BOD < 30 mg/L, SS < 30 mg/L but may rise to >100 due to algal solids in lagoon or pond systems. 


The process by which suspended particles in waste water settle to the bottom. 

Sequestration (of carbon)

Carbon sequestration means the collecting or trapping of carbon dioxide from the atmosphere. This can be done in a number of ways. The most popular is through using land and trees to suck it up. These areas are then called 'carbon sinks'. Another approach to mitigating global warming is based on capturing carbon dioxide (CO2) from large sources such as coal-fired power stations and then storing it below ground instead of releasing it into the atmosphere. This approach is still in the research and development stage.


Sewage refers to material transported in sewerage system.  Sewage is collected from all internal household drains; it contains all the contaminants of grey water and urine, in addition to high concentrations of faecal material from toilets and wastes from industrial and commercial premises. Sewage can therefore contain a range of human infectious enteric pathogens and a range of physical and chemical contaminants

Sink (for greenhouse gases)

In the context of climate change, a sink is a natural or man-made process or activity that absorbs and stores greenhouse gases (e.g. carbon dioxide) from the atmosphere (e.g. by forests and oceans).


Generally refers to a mixture of rain and snow or falling snow that is melting into rain 


Sludge is the inorganic suspended solids (see separate entry) which settle out from sewage. 


Smog (contraction for 'smoke fog') is a fog in which smoke or other forms of atmospheric pollutant have an important part in causing the fog to thicken, and have unpleasant and dangerous physiological effects 


Precipitation of ice crystals, most of which are branched (sometimes star shaped). 


An element found endemic in the environment. High concentrations of sodium in soil relative to calcium and magnesium cause sodicity (ESP > 6 or SAR >3). This is a condition where the positively charged sodium ions cause the soil particles to repel each other, resulting in soil swelling, dispersion and reduced soil permeability. 

Soft water

Water with light concentrations of calcium and magnesium, and which lathers readily with soap or detergent. 

Solar concentration (power generation)

Concentrating solar power systems are ways of capturing the sun’s radiant energy from a large area and concentrating it usually with mirrors or lenses to a point where it can be converted into high temperature heat used to generate electricity in a steam generator. Concentrating solar power plants use different kinds of mirror configurations. There are three main types: trough systems, dish/engine systems, and power towers. Each concentration method is capable of producing high temperatures but they vary in the way they track the Sun and focus light. A working fluid is heated up to 150-350 °C as it flows through the receiver of the focused light and is then used as a heat source for a power generation system.

Solar photovoltaics (power generation)

Photovoltaic power generation is the field of technology and research related to the application of solar cells for energy by converting sunlight directly into electricity. Photovoltaics are best known as a method for generating solar power by using solar cells packaged in photovoltaic modules, often electrically connected in multiples as solar photovoltaic arrays. Photons of sunlight impact with atoms in the receiving substances of the solar cells and electrons are knocked into a higher energy state, creating electric potential.

Solar radiation

Solar radiation is electromagnetic radiation from the Sun. Solar radiation has a distinctive range of wavelengths (spectrum) determined by the temperature of the Sun, peaking in visible wavelengths.

Source (of greenhouse gases)

Any process or activity that releases a greenhouse gas, an aerosol or one of their precursors into the atmosphere.

Southern Oscillation Index (SOI)

The Southern Oscillation Index (SOI) is calculated from the monthly or seasonal fluctuations in the air pressure difference between Tahiti and Darwin.  Sustained negative values of the SOI often indicate El Niño episodes. These negative values are usually accompanied by sustained warming of the central and eastern tropical Pacific Ocean, a decrease in the strength of the Pacific Trade Winds, and a reduction in rainfall over eastern and northern Australia. The most recent strong El Niño was in 1997/98.  Positive values of the SOI are associated with stronger Pacific trade winds and warmer sea temperatures to the north of Australia, popularly known as a La Niña episode. Waters in the central and eastern tropical Pacific Ocean become cooler during this time. Together these give an increased probability that eastern and northern Australia will be wetter than normal. 


A shallow bore inserted in soft sediments to draw up water from under the ground. 

State Environmental Planning Policy (SEPP) 14

NSW Government policy to ensure that the coastal wetlands are preserved and protected; prepared under the Environmental Planning and Assessment Act 1979. 


Rainfall which runs off roofs and roads and other surfaces and flows into gutters, streams and waterways where it eventually flows into the bays. This water can carry with it all sorts of contaminants. Some are obvious such as plastic bags or detergents from people washing their cars; others are not so obvious such as nutrients and heavy metals. 


Distinct layers of water in a dam or weir pool formed when there is little movement to cause intermixing-usually in summer when deeper layers of water become cold and deoxygenated. These changes may, in turn, induce other water quality changes. 


The highly stratified region of the atmosphere above the troposphere extending from about 10 km to about 50 km above the earth’s surface.

Stratus Cloud

Low cloud forming a uniform layer. 

Stressed river

Assessment made by the Department of Land and Water Conservation that determines appropriate management strategies for water allocation and flow management in uncontrolled streams. A classification based on environmental and water-use criteria. 

Surface water

Water on the surface of the land, for example in rivers, creeks, lakes and dams. 

Suspended solids

Some substances, such as soil, have particles that cannot dissolve. The bigger particles settle if the water is not disturbed, but some are too small to settle out and stay suspended. These particles are big enough to scatter light and make the water appear murky. Solids such as mud can be removed by letting the water stand for several years or by filtering it. 

Sustainable (as applied to water resource management)

Management that will meet current needs while conserving natural ecosystems so they can also meet future needs.  
System yield The annual level of total demand that can be supplied by a water supply system subject to an adopted set of operational rules and to a typical demand pattern while maintaining a given level of security of supply 


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Target (water quality)

A level of water quality to be achieved in a specified time frame as a step towards the desired long-term objectives. It is derived from comparing available water quality data/information with the water quality objectives, and considers social and economic factors. 

Tertiary treatment 

Includes treatment processes beyond secondary or biological processes which further improve effluent quality. Tertiary treatment processes include detention in lagoons, conventional filtration via sand, dual media or membrane filters which may include coagulant dosing and land based or wetland processes. 

Top-release (of water)

Better-quality water released from the top layers of a dam. 

Total dissolved salts (TDS)

A measurement of the total dissolved salts in a solution. Major salts in recycled water typically include sodium, magnesium, calcium, carbonate, bicarbonate, potassium, sulphate and chloride. Used as a measure of soil salinity with the units of mg/L. 

Trade winds

Trade winds are a pattern of winds that blow in the equatorial and near-equatorial regions of the Earth. In the Northern Hemisphere they blow from the northeast direction. In the Southern Hemisphere they blow from the southeast. In other words, in both hemispheres their general direction is from east to west. In northern Australia during the wet monsoon season the trade winds are usually replaced by moist winds from the northwest i.e. from the northern Indian Ocean.

Treated wastewater

Water that has been processed in a wastewater treatment plant (also known as sewage treatment plant). The solid and liquid components of the wastewater are separated, and natural processes are encouraged whereby bacteria break down the waste and reduce its potential impact on the environment. The extent of treatment depends on the standard required in the receiving environment 


A river or creek that flows into a larger river. 

Trigger values

The ANZECC 2000 Guidelines state that: 'These are the concentrations (or loads) of the key performance indicators measured for the ecosystem, below which there exists a low risk that adverse biological (ecological) effects will occur. They indicate a risk of impact if exceeded and should 'trigger' some action, either further ecosystem specific investigations or implementation of management/remedial actions.' Note that on this website, the trigger values from the ANZECC 2000 Guidelines are also referred to as guideline levels or numerical criteria. 


The boundary between the troposphere and the stratosphere.


The troposphere is the lowest part of the atmosphere, contains most of its mass, and is where clouds and weather phenomena occur. The troposphere extends from the surface to about 10 km in altitude at mid-latitudes (ranging from 9 km at high latitudes to 16 km in the tropics on average). In the troposphere, temperatures generally decrease with height.


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.


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Ultraviolet radiation

Non-visible electromagnetic waves with a wavelength shorter than visible blue and violet light.

Uncontrolled streams

Streams that are largely free of structures that control flow, such as major dams.


The rise to the surface of cold, deep ocean waters. 

Urban salinity

See Salinity. 


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A variable is a measurable factor or characteristic, or attribute of an individual or event; in other words, something that might be expected to vary over time or between individuals or events.


 Variability refers to how ‘spread out’ a group of scores or measurements is. 


An infectious agent that replicates only inside the living cells of other organisms.