How can a reservoir be more than 100%?

How can a reservoir be more than 100%?

Our reservoirs supply homes and businesses across South Australia. At full capacity, they can collectively hold just under a year’s supply of water for Adelaide. In recent weeks, the heavy rainfall has resulted in a large amount of inflow into our reservoirs. For the first time in over 10 years, our combined reservoir level has exceeded 100% and multiple reservoirs are still full.

You may be wondering – how can a reservoir be above 100% capacity?

It is possible for a reservoir to measure more than 100%. A reservoir can hold slightly more water than the set capacity levels we report against, and spills once it’s above full capacity. Essentially, any increases above 100% mean the reservoir is spilling. However, we perform controlled releases of water at the Mount Bold and Myponga reservoirs before they reach 100% capacity. Our Mount Bold and Myponga reservoirs have adjustable gates to manage outflows, and all other reservoirs apart from Barossa have spillways to discharge water collected above capacity.

For a reservoir to spill, the water level must be above the spillway, which is positioned at full capacity. As the water level in the reservoir rises above the base of the spillway, the volume increases beyond 100% until inflows begin to drop and the reservoir is no longer spilling.

Click diagram below to enlarge
How can a reservoir be more than 100%?

  • Major faults

  • Reported

  • HMAS Australia Road
  • Henley Beach South
  • 18/12/2017
  • Water Off
  • 18/12/2017 3:26 PM - We are on-site responding to an incident in Henley Beach South. Our crews may remain on site to perform further work. Traffic restrictions may also apply. Reference Number WO:06151098

  • See all major faults

  • Scheduled works

  • Underway
  • Port Rd
  • Woodville
  • 18/12/2017
  • Supply Interruption
  • Estimated start time (water off): 20/12/2017 10:00 AM
    Estimated restore time (water back on): 20/12/2017 02:00 PM

    We’re committed to improving your services and are undertaking maintenance work in Woodville. Water supply in the surrounding area may be impacted during the above times. Traffic restrictions may also apply.


  • See all scheduled works