A catchment is an area of land where water collects when it rains, often bounded by hills. As the water flows over the landscape it finds its way into streams and down into the soil, eventually feeding the river. Some of this water stays underground and continues to slowly feed the river in times of low rainfall. Every inch of land on the earth forms part of a catchment.
Catchments can range greatly in size from small urban sub-catchments such as Prospect Creek that feeds part of the larger Georges River Catchment, to massive catchments such as the Murray-Darling Basin that spans three states.
The Georges River catchment stretches from Botany Bay on the east coast of New South Wales west towards Prospect Reservoir and south into bushland around Campbelltown and Appin.
Catchments are complex and something happening in one part of the catchment can have a big impact on other parts. In Australia, the past 200 years has seen big changes to our catchments. Natural landforms such as bushland and small creeks have been replaced in many areas by houses, roads, footpaths and stormwater pipes. This has had a large impact on our creeks and rivers.
Marion Huxley, Georges Riverkeeper Aquatic Ecologist, explains what a catchment is. This video is part of the education resource for Stage 1 primary school educators, developed by Georges Riverkeeper in collaboration with Georges River Environmental Education Centre.
Why are catchments important?
The idea of catchments is useful, as it is the standard functioning unit of the landscape: water, soil, plants and animals are all linked together within a catchment, and any activity that occurs within a catchment will affect the whole catchment. Healthy catchments are important for human survival, as it is where our food is grown and where all the water we drink comes from.
What is a healthy catchment?
A healthy catchment is one that is still able to function as a catchment should. It should be able to filter and clean water as it flows overland and seeps through the ground, and there should be lots of opportunities for water to seep into the ground so that it can be used by plants.
What is wrong with our catchments now?
Over the last 200 years Australians have been busy building cities and towns. Land has been cleared, roads and footpaths laid, farms created and stormwater systems installed. The Georges River catchment is one of Australia's most urbanised and developed catchments and this has led to poor health throughout most of the catchment. Stormwater pollution, sedimentation, lack of infiltration, loss of biodiversity and invasion of weeds are some of the primary problems that we are facing. As a result the health of the River itself has declined.
Make a model of a catchment
Students construct three-dimensional models of water catchment basins using everyday objects to form hills, mountains, valleys and water sources. They experiment to see where rain travels and collects, and survey water pathways to see how they can be altered by natural and human activities.