Managing our water supply in the wet and dry

December 3, 2020

cotter dam, bendora dam, googong dam, water supply, floods

Cotter Dam, Bendora Dam and Googong Dam at 100% capacity with flow over the spillways. 

Icon Water manages four water supply dams across the ACT’s (Australian Capital Territory) water supply network, transferring the best sourced raw water from Corin Dam, Bendora Dam and Cotter Dams in the Cotter River catchment, and Googong Dam in the Queanbeyan River Catchment. These dams were progressively built and modified over the past century, including the latest enlarged Cotter Dam in 2013 to supply secure drinking water for Canberra and the Queanbeyan community.  

Over the winter and spring, we have received above average rainfall. At the start of November, our current combined dam levels were sitting at 98% full. This is an increase of over 54% since early February 2020 when levels dropped to below 45%, following a very hot summer, and two of the driest years on record.  Our total dam storage capacity is now almost full for the first time since 2016.  

Bendora, Cotter and Corin dams are all 100% full. Googong is currently supplying the Canberra and Queanbeyan community and although it did reach 100% in November 2020, it has not maintained this level due to supply requirements. 

As each of the dams reach capacity, these dams' structures are designed to allow the water to naturally cascade over the spillways. The water spilling from the dam provides water downstream to river ecosystems and supplements the daily environmental flow release. 
Icon Water manages the water supply and operations of our dams daily through a team of analysts and modellers who are constantly monitoring many factors relating to our water supply and security. Both rainfall and consumption directly impacts our water storage position. 

How do Icon Water supply dams' function during a flood event?

Although our dams are not flood mitigation dams, when they are full, our dams significantly reduce the risk of downstream flooding as water leaves the reservoir at a slower rate than it enters. This reduction in peak flow helps to mitigate flood damage downstream. A joint, independent study commissioned by Icon Water and QPRC (Queanbeyan-Palerang Regional Council) found that just by its existence, the Googong Dam reduced the peak of the flood by 47% in Queanbeyan in 2010. 

In terms of structural integrity and safety, when at capacity, the ACT’s dams all meet the Australian National Committee on Large Dams (ANCOLD) design standards. The standards require dams in Australia to have capacity to pass extreme floods and to safely pass 10,500 cubic meters of water per second. This is approximately four times the normal flow over Niagara Falls.

Icon Water’s team of safety and engineering experts implement a proactive dam safety program which involves regular safety inspections at each of our dams. We also have instrumentation monitoring across all four of Icon Water’s dams to ensure they are operating as intended.   

What is Icon Water’s role during a flood event?

In the event of flooding, Icon Water is responsible for the safety and operation of our dams. Our four dams are built in line with ANCOLD design standards and can withstand large flood events. 

Icon Water has no particular role in flood management, other than monitoring how the dams work during the event. All other flood related operations are undertaken by the Bureau of Meteorology (rainfall and streamflow projections and warning) and the ACT and NSW State Emergency Service (SES). 

You can find out more about dam storage levels at iconwater.com.au/damlevels

Seeking more information on Googong Dam and flooding

• Flood warnings and flood level forecast – Bureau of Meteorology 
• Flood damage and road closures, crowd control - Queanbeyan City Council Phone: 1300 735 025

Maintaining Water conservation across our community

While we are excited to see dam levels increase further and potentially reach 100% capacity, it’s important that as a community we continue to remain focused on maintaining our water wise habits. 

Australia is the second driest continent on Earth, and it is very likely that we will experience significant drought again in our future. We really want to encourage Canberrans to maintain their water wise habits so that we can protect our water supply for generations to come. Canberra has been under Permanent Water Conservation Measures (PWCM) since 2010. 

Icon Water will continue to proactively encourage the community to maintain their water wise habits and to apply the PWCM currently in place. These measures are common-sense rules to prevent water wastage and include things such as watering gardens during specific hours when evaporation has a reduced impact and only cleaning vehicles and buildings using a high-pressure low volume hose or a hose fitted with a trigger nozzle. The measures will remain in place permanently in the ACT.   
  
You can find out more about the rules around water use in the ACT along with simple tips for saving water on our website – iconwater.com.au/savewater