WHAT IS A CATCHMENT AREA?
A catchment area or basin is land which is bounded by natural features such as hills or
mountains, from which all runoff water flows to a low point - like water in a bathtub flowing to
the plug hole, or water that falls on a roof flowing to a downpipe. In the case of a natural
catchment area, the low point could be a dam, a location on a river, or the mouth of a river
where it enters the ocean.
Catchment areas vary in size and make-up. Large catchment areas such as those drained by the
Murray and Darling Rivers are bordered by mountain ranges and include major drainage
networks of creeks and rivers. Large catchment areas are made up of hundreds of smaller 'subcatchment areas'. These may be bordered by low hills and ridges and drained by only a small
creek or gully.
Figure 1 shows a large catchment area that is broken into a number of smaller sub-catchments.
The way each of these small catchment areas is managed affects the overall well-being of the
larger catchment area.
Figure 1 A large catchment can be broken into a number of smaller sub-catchments.
WHAT IS IN A CATCHMENT AREA?
A range of natural resources and land uses will be found in a catchment area from the
headwaters to the mouth of the river, but these may vary greatly. Some of the following may
be found:
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land
water
natural vegetation
crops and pastures
gardens
wildlife
people
domestic animals
homes
industry
transport routes
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recreation facilities
cities and towns
farms
National Parks
Forestry areas
dams
irrigation systems
refuse
sewerage system
windmills and pumps
Water movement in a catchment area
Water is the linking factor in a catchment area. The water cycle is shown in Figure 2. The sun's
energy transfers water from the sea to the atmosphere in the form of water vapour. This
process of evaporation also takes place on land. Plants add water vapour through
transpiration. People, animals and machines add small amounts of water vapour as well, by
means of respiration and combustion. The water vapour condenses to precipitation, which
may fall as rain, snow, sleet or hail. Some precipitation evaporates while falling and returns to
the atmosphere. Most precipitation soaks into the soil (infiltration). Some of the soaked water
returns to the surface and is evaporated. Part of it sinks to the watertable. Any excess water
runs off the land and is carried away by streams and rivers (surface runoff).
Source: Catchment Care Education Kit - Information for Teachers and Students Activities Department of Primary Industries.
Figure 3.