Metro region weekly water update for 21 September 2017

• September water use is 13.2 billion litres versus a target of 12.9 billion litres D

   

• Dam storage levels are 42.4% B

   

• Flow into dams – 67.5 billion litres of streamflow since 1 May 2017 B

   

• September rainfall – 35.4mm to date.  Average rainfall for September is 81.3mm

   

Wet wet wet… or is it?

With the wet weather around for the next seven days straight let’s take a look at our rainfall situation…

In the south west of Western Australia rainfall occurs mainly from the end of autumn to the start of spring.   

Rainfall varies greatly from one year to the next and from one decade to the next.  Despite this large natural variability, underlying longer-term trends are evident.

In its State of the Climate 2016 report, the Bureau of Meteorology says the drying trend is particularly strong over southwest Western Australia, with rainfall since 1970 around 19 per cent less than the long-term average.  Since 1996, this decline from the long-term average has increased to around 25 per cent.

But why are we so interested in rainfall at the Water Corporation?  We’re interested because the reduced rainfall has had a significant impact on dams and groundwater sources limiting the amount of water available for public water supply.   This has seen the Water Corporation invest over $2.2 billion during the last decade or so in new sources of water that don’t rely on rainfall.

Since 1 January 2017 we have received 724.6mm of rainfall compared to the cumulative average of 759.4mm (January to September).

It looks like we're in for a wet long weekend with as much as 20mm expected on Sunday and then up to 25mm on Tuesday, with the possibility of more than a month’s worth of rain over the next week.

Dam levels

It’s estimated that we need about 400mm (+/- 100mm) of annual rainfall to start the streams flowing to Perth’s dams. 

Over the last seven days Perth’s dam storage levels increased from 42.5% to 42.8% (0.3 percentage points).  This was partly due to them receiving 500 million litres (222 Olympic swimming pools) of inflow from streams.  This brings the total streamflow to 68 billion litres since 1 May 2017.  The post-1975 average for annual streamflow is 189 billion litres.  It’s worth noting that Perth’s dams also store water transferred from our two desalination plants.

Water use

Our average daily water use last week was 660 million litres, which was above the forecast of 629 million litres per day.  This water was used by the two million people who are connected to the Integrated Water Supply Scheme, which delivers water to Perth, parts of the south west, Agricultural and Goldfields regions. 

Our financial year to date water use is 48.7 billion litres - slightly more than the 48.1 billion litres we forecasted. 

Sprinkler roster compliance

The two-day-per week Sprinkler roster now applies, and this week our inspectors issued 46 warnings and 33 fines in the metro region.  This is compared to 27 warnings and 28 fines the previous week.   Year to date we have taken a total of 7,417 actions (warnings + fines) compared to 8,176 actions for the same period in 2016.    

General news

And, this is our last call to visit the Dam Cam before it retires next week… https://www.watercorporation.com.au/water-supply/our-water-sources/dams/dam-cam.  We’re pleased to say Dam Cam has had more than 1,000 views on our website since it went live last month -so we’re working on a plan to bring it back next winter.