About the Catchment Area : General Info

About the Catchment Area

General Information
In this section discover more about certain features of a catchment
What is a catchment?
Rainfall in the Onkaparinga catchment area?
The water cycle
What makes for a healthy waterway?
What is a riparian zone?

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What is a Catchment?

A catchment is an area of land that collects water, which drains to the lowest point in the area which could be either a lake, a dam, or the sea. Rain falling on the land will make its way to this lowest point, via creeks, rivers and stormwater systems.

As well as rivers, creeks, lakes and dams, a catchment also includes groundwater, stormwater, waste water, and water-related infrastructure.

We all live in a catchment and caring for our waterways is everyone’s responsibility.

Go to more information on creeks and rivers in the Southern suburbs of Adelaide.

Rainfall in the Onkaparinga catchment area

In the Onkaparinga Catchment area our mean annual rainfall varies from over 1100mm in the Adelaide Hills to around 400mm near the sea.

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The Water Cycle

Before looking at the water cycle we should first give some consideration to water itself. Of all water in the world, about 97% is sea water, about 2% is polar ice and only a very small 1% is fresh water. The amount of water in the world remains never changes.

The chemical composition of water is H2O. This means there are 2 hydrogen molecules to 1 oxygen molecule. The three forms of water are:

Solid - snow, frost, hail and ice. (Water freezes at 0° Celsius and forms ice;)
Gas - water vapour, steam. (Water turns to a gas at 100° Celsius)
Liquid - clouds, rain, oceans, lakes, rivers, fog.
The quantity of water found on the earth remains constant and it is billions of years old. It continually cycles around and around in a process called the water cycle. For example the water you used to brush your teeth with this morning is more than 4 billion years old.

The water cycle has four main processes. These are:-

Evaporation - Is the process whereby water moves from the surface of the earth into the atmosphere. Heat from the sun soaks up water from the ocean and other bodies of water, such as rivers, lakes and puddles. The water vapour rises into the air and is then transported by the wind.
Transpiration - This is the other process whereby water moves from earth to the atmosphere. Trees, shrubs, grasses and other plants all need water to survive. They take up water from the soil by their roots so that they can grow. Just like in the process of evaporation the sun creates heat which transpires this water into the air through tiny holes in the underside of leaves.
Condensation - Under certain conditions the water vapour stored in the atmosphere begins to form tiny droplets of water vapour. This process is called condensation. The condensed water vapour appears as clouds. Another form of condensation is the formation of water droplets or ice crystals directly on cold surfaces: condensation on ground surface is known as dew or frost. The wind moves the clouds around the atmosphere.
Precipitation - Precipitation occurs when the water vapour cools and becomes too heavy to stay in the sky. As the clouds are moved around by the wind they begin to cool. This turns the water vapour into droplets, which results in precipitation. This occurs as either rain, hail, sleet, or snow falling to the ground. The water cycle then begins over again.

Information on the watercyle was sourced from: Gippsland Water
http://www.vicwater.org.au/education/

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What makes for a healthy waterway?

There are many opinions as to what constitutes a healthy waterway. What follows is a definition comes from the “Healthy Rivers, Healthy Communities & Regional Growth - Victorian River Health Strategy” department of Natural Resources and Environment, 2002.

An ecologically healthy river will have flow regimes, water quality and
Channel characteristics such that:

in the river and riparian zone, the majority of plant and animal species
are native and no exotic species dominates the system;
natural ecosystem processes are maintained;
major natural habitat features are represented and are maintained over time;
native riparian vegetation communities exist sustainably for the majority of its
length;
native fish and other fauna can migrate up and down the river;
linkages between river and floodplain and associated wetlands are able to
maintain ecological processes;
natural linkages with the sea or terminal lakes are maintained; and
associated estuaries and terminal lake systems are productive ecosystems.

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What is a riparian zone?

A riparian zone is the area of land immediately adjacent to a body of water (such as a river, creek, lake or pond) that influences or is influenced by the water body. Riparian land includes:

The land alongside small creeks and rivers, including the riverbank
Gullies and dips, which sometimes run with surface water
Areas surrounding lakes;
Wetlands on river floodplains which interact with the river in times of flood.

Riparian zones generally have a great diversity of animals and plants compared to adjoining habitats. The vegetation found in riparian zones ranges from aquatic plants to mature trees and understorey vegetation.

Why are riparian zones important?
Stream ecology and water quality is greatly influenced by riparian zones. Riparian zones perform a number of important functions:

Habitat – Riparian zones are important to both aquatic and terrestrial animals. Riparian vegetation provides organic matter to feed invertebrates such as dragonflies and daphnia which in turn are a food source for frogs and fish. The vegetation also shades and buffers the aquatic environment against high temperatures in summer. Land-based animals use the riparian zone to shelter, hunt and breed. Many animals also use the riparian zones in areas with little remnant vegetation as transport corridors.
Channel shape and bank stabilisation – River and creek banks are vulnerable to erosion from fast flowing water. Riparian vegetation protects the river channel from erosion. Riverbanks that are well vegetated with plants such as rushes and reeds will protect soil by reducing the velocity of the water, trapping sediment and binding the banks. This will reduce or prevent erosion and allow natural pools and riffles to form, creating important habitats for aquatic organisms.
Water quality – Riparian vegetation improves water quality by filtering runoff from the catchment and removing pollutants. Pollutants such as organic and inorganic nutrients, herbicides, pesticides and sediments can all be absorbed or trapped by the vegetation before it enters the water body.
Recreational and aesthetic values - Healthy creeks and rivers are peaceful and beautiful. They are important to keep for both us and future generations so we can enjoy them and learn from them.

Threats to riparian zones

Clearance of vegetation for agriculture has resulted in a lack of indigenous vegetation in many riparian zones. As a result bank instability and erosion threaten many riparian zones.
Woody weeds and exotic trees (such as willows and ash) are also a problem along creek and riverbanks as they dominate the ecosystem and reduce diversity.
Unrestricted stock access is a further threat to riparian zones because stock remove protective vegetation causing destabilisation of banks and increased erosion.
Over use of pesticides and fertilisers on home gardens and farm crops run-off into riparian zones destroying habitats.

Are riparian zones threatened? Yes, go to Issues and Problems

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