Catchment

Brief description

A catchment is an area of land that catches water from rainfall (or snow) and feeds it into a waterway such as a creek, river system, lake, wetland or dam, or into groundwater.

More information

How does a catchment work?

Water enters a catchment when rainfall (or snow in the really cold places) lands within the catchment area and makes its way down towards the rivers, lakes, wetlands or dams. Along the way, some water is absorbed into the ground, some evaporates and some is used by plants. The remaining water that continues to run over the surface of the land is known as surface runoff.

Why does this water "run off"? The main reason is gravity - water usually flows from higher areas to lower areas. A catchment begins at the highest point and the water flows to lower areas with the force of gravity, eventually ending up in a body of water such as a river or a lake.

Imagine rain falling into a catchment area and filling up the rivers and lakes. There's also a lot going on underground where the water seeps deep into the soil. This groundwater, which lies beneath the surface, can have an impact on our river systems. You can visit the Groundwater section on this site to find out more about how this happens.

Why do we need to know about catchments?

Water can move easily from one place to another, even through the tiniest gaps in the soils, so in a catchment, where the water is all connected, anything that happens in one place can eventually affect other areas of the catchment.

Imagine dropping a leaf into a small stream. As the water flows, the leaf will slowly make its way into the larger part of the river, and might even end up at the mouth of the river as it reaches the ocean. Now imagine that leaf is a plastic bag or a bucketful of toxic waste and consider how the environment could be damaged as these pollutants are carried by the water through the catchment.

If we know where the different catchments are in Western Australia, then we know where our streams, creeks and rivers start and where they end up. This means that we can learn to look after the whole area that catches the water which ends up in our river.

Did you know?