Why is it that when Perth gets a heavy rainfall, our dam levels don’t automatically rise at the same time? This is a transcript of our animated video, 'Our dam catchments and rainfall' which explains how Perth's dry catchments are affecting our dams.
[Voiceover]: Here’s a question: why is it that when Perth gets a heavy rainfall, our dam levels don’t automatically rise at the same time?
The answer: it’s all to do with how much moisture is in the soil in our catchment areas.
A catchment, in case you didn’t know, is an area where water is collected by the natural landscape, and it’s usually surrounded by high features such as hills or mountains.
The soils in our catchments act like a sponge, soaking up moisture, storing it in underground aquifers, and gradually releasing it into our rivers and streams, which then flow into our dams.
Years of below average rainfall means that Perth’s catchments areas have become drier and drier.
So when the rains do come, they are soaked up by the soil, which leaves us needing a lot more rainfall for the water to eventually find its way into our dams.
What’s more, because Perth’s groundwater levels are dropping too, it takes even longer for rainfall to seep into the ground, soak the catchments and get the streams flowing.
So, there’s the answer. It’s all to do with Perth’s dry catchments.
The fact is, even if we do get decent rainfall in any one year, we’ll still get a lot less inflow to our dams than we would have from the same amount of rainfall, several years ago.