Metro weekly water update 5 July 2018

Note: 1 billion litres = approx. 400 Olympic swimming pools.  Please note these figures are rounded (except for rainfall) to the nearest whole number.

Water use

Average daily water use over the last week was 602 million litres, which was slightly above the forecast of 596 million litres.  Since 1 July 2017 we have used 285 billion litres of water, which is 7 billion litres below the 292 billion litres we had forecast.

Dam levels

Over the last seven days, Perth’s dam storage levels have increased (by about 6 billion litres) from 148 billion litres to 154 billion litres of usable storage. Perth’s dams store water from three different sources… groundwater and desalinated seawater transferred from treatment plants as well as streamflow (produced by rainfall).

Streamflow

Over the last seven days Perth’s dams have received about 4 billion litres of streamflow.  For more on streamflow see this week’s General water news below.

Sprinkler roster compliance

The Winter Sprinkler Switch Off now applies, and our inspectors issued 180 warnings and 22 fines last week.  Since 1 January 2018 we have taken a total of 4995 actions (warnings + fines) compared with 6047 actions for the same period in 2017.

Annual rainfall

Perth has received 370.2mm of rainfall since January this year.  According to updated figures released by the Bureau of Meteorology the cumulative mean rainfall (1994-2017) for the Perth metro for the January to July period is 450.1mm.

General water news

What is streamflow?

Streamflow is the flow of water in streams, rivers or channels into our dams. It is the main mechanism by which water moves from the land to the dams. 

Water flowing in streams or channels into our dams comes from runoff from adjacent hillslopes, which we call catchments. 

At the end of winter, streamflow stops, and it takes many, many millimetres of rainfall to get it started again.  This is because these days we get less rainfall due to climate change and the catchments are dry so they quickly soak up the rainfall before it reaches the streams or channels.  We often refer to our catchments as sponges that need to become fully soaked before they release any water to the streams or channels.

Watch this YouTube clip for more on streamflow.