Coulburn-Murray Water manages more than 9 million megalitres of water across 16 storages

 
 
   
 
   Provided by BoM      Provided by BoM  
           

   
   
   Provided by BoM      Provided by SES  

 

Operating and maintaining 16 water storages across northern Victoria that can hold 9,000,000 megalitres of water - or 70% of the total water storage capacity in Victoria - is an ongoing and major part of Goulburn-Murray Water's (G-MW) business.

After a decade of drought moving into unprecedented rain and flooding in some parts of Victoria, we've been closely monitoring our storages not only for their ability to recover from these conditions but also the potential to deal with any additional rainfall experienced across the catchments.

While the primary role of our water storages is to harvest and store customers' water entitlements, G-MW provides flood mitigation benefits where possible. Pre-releasing water from a G-MW water storage can influence the rate at which a storage fills and is a valuable tool to balance entitlement reliability and flows downstream of a storage.

Storage Status Update  (Updated 9:30 AM, Thursday 17 April 2014)

This information covers storages where non-operational releases are taking place. The forecast releases are an indication only and are to be used as a guide and may change depending on weather conditions. Please check this information daily if your property is subject to inundation at high river levels while releases above minimums are taking place at our gated spillway dams – see FAQs below for an explanation of pre-releases.

Storage releases may change in response to inflows, weather forecasts and observed rainfall.  For real-time river levels please visit the Bureau of Meteorology River Levels website (see link above). 

Loddon Storages

Releases from Cairn Curran, Tullaroop and Laanecoorie reservoirs are meeting normal operating requirements.

Releases from Loddon Weir increased on 7 April to deliver an environmental flow which will continue until 22 April. The target flow downstream of Loddon Weir during this event is 100 ML/d. Flows in the Loddon river are expected to remain well below flood levels. From 23 April the target flow will be 25 ML/d dowstream of Loddon Weir.

Lake Buffalo

Lake Buffalo releases are being maintained to meet downstream flow requirements. Please see the Bureau of Meteorology website (see links at top of this page) for information on real time river levels and flood warnings.

Lake Nillahcootie

Releases are being made to meet normal operating requirements in the Broken system.   

Lake Eppalock

Releases from Lake Eppalock are currently meeting normal operating requirements.   

Lake Eildon

Releases from Lake Eildon are currently meeting normal operating requirements, including the delivery of environmental flows downstream of Goulburn Weir. The release yesterday, today and a forecast for the next three days are outlined below:

Last Updated: 9:30am, 17 April 2014

Releases from Lake Eildon

Date

Month

Release (ML/d)

Yesterday 16 April 2014 1,000
Today 17 April 2014 1,000
Forecast 18 April 2014  1,000*
Forecast 19 April 2014 1,000*
Forecast 20 April 2014 1,000*

 

Further Information for Lake Eildon:

Tributary Flows:

There are a number of other tributaries that contribute to the river levels downstream of Lake Eildon such as the Acheron, Rubicon and Yea Rivers. Levels in these tributaries can be monitored on the Bureau of Meteorology website.

Goulburn Weir

Current releases from Goulburn Weir are meeting normal operational requirements, including the delivery of environmental flows downstream of Goulburn Weir. 

 

The release yesterday, today and a forecast for the next three days are outlined below:

 

Last Updated: 9:30am, 17 April 2014

Releases from Goulburn Weir

Date

Month

Release (ML/d)

Yesterday 16 April 2014 830
Today 17 April 2014 830
Forecast 18 April 2014  830*
Forecast 19 April 2014 830*
Forecast 20 April 2014 830*

* Forecast releases to meet consumptive and environmental flow requirements downstream of Goulburn Weir.

This is a forecast of flows only and is subject to change. Flows in the Goulburn River may increase at any time due to rainfall in the river catchment. The 'River Levels: Provided by BoM' link under the heading of this page provides access to river height information for a number of sites along the Goulburn River.

Dams - How they workdams animation tool banner

Ever wondered how a dam works? How is the water released and where does it go?

Our 3D animation is designed to show you what a dam looks like, the infrastructure, and challenges in managing water. It allows you to explore different parts of the dam with a slider that demonstrates the effect of changes in water levels.

 

 

Frequently Asked Questions

Are there different types of dams and what are they? 

What is a pre-release?

Is this the first time G-MW have undertaken pre-releases?

Don't pre-releases minimise the effects of flood on downstream users?

Why not just release lots of water if we know it is going to rain?

What role do G-MW dams have in flood mitigation?

When did pre-releases start at Eildon?

How is water released from Eildon?

Can we see the water being pre-released from Eildon and can we get photos?

What is a spillway and what does it do?

Are there different types of dams and what are they?

Yes.  G-MW operates dams with two different types of spillways, fixed crest spillways or gated spillways.
 
Fixed crest spillway dams generally have relatively small outlet works and operate on a ‘fill and spill’ basis. As inflows enter the dam, the water level in the dam increases until it reaches the spillway crest level where it will overflow into the downstream river channel. The fixed crest level is at the Full Supply Level (FSL) of the dam and is the point at which the dam is 100% of capacity. The embankment of the dam is designed to allow the water level to naturally surcharge above 100% of capacity and allow the spillway structure to ‘throttle’ outflow. Dams of this type provide some flood mitigation by attenuating the flood peak. There is no operational control from the dam operator in passing floods through these types of dams.
 
Gated spillway dams are configured with large gates in the spillway that enable water to be stored above the spillway crest level. As the dam’s FSL is above the spillway crest level, the gates must be closed to allow the dam to fill to 100% of capacity. During winter and spring, water is harvested in the dam by following a target filling curve that balances resource increases against a degree of flood mitigation. Flood water is passed through the spillway by opening the spillway gates. The embankments on G-MW’s gated spillway dams are not designed to be surcharged in the same way fixed crest spillway dams operate. The flood operating procedures for gated spillways aim to pass inflows through the dam while maintaining the level within the dam at or below FSL. Generally the operation of gated spillway dams involves using pre-releases as any air space (the available volume between the lake level at the beginning of an event and FSL) to delay the onset of flooding and reduce the flood peak. The amount of flood mitigation that can be provided depends on the amount of air space available and the size of the flood. Only 3 of G-MW’s 16 dams have gated spillways – Eildon, Buffalo and Cairn Curran.

GMW Water Surcharge Policy - Flood Operations Headworks Structures [80 KB] 

What is a pre-release?

A pre-release can manage the rate of a storage filling and be a valuable management tool to balance G-MW customer’s water entitlement (that is stored in water storages) and downstream flood impacts. It’s a little like letting the plug out of a bath for a moment when it is nearly full.

GMW Pre-release from Dams Policy [80 KB]

Is this the first time G-MW have undertaken pre-releases?

No. The pre-releasing from Eildon is normal operating procedure for the dam and has been done each time the dam has been in this situation - that is, near full during winter and spring. Pre-releases are also made from our other gated spillway dams, Buffalo and Cairn Curran. Due to the design of the spillway, there is limited opportunity to pre-release from our other dams. Where possible G-MW tries to maintain some  "airspace"  in all the dams during winter and spring.

Don't pre-releases minimise the effects of flood on downstream users?

The pre-release   of water from any storage will not minimise the effects on downstream users, it provides a balance between resource harvesting and flood mitigation.  If we receive a large inflow to the water storage, there is still the risk of flood downstream.

Why not just release lots of water if we know it is going to rain?

Unfortunately it’s not that simple.  Water in a storage is owned by customers and a storage simply holds it for them until they are ready to use it. The level in the water storage during winter and spring is managed in accordance with rules and procedures that G-MW must adhere to. The rules limit the opportunity for G-MW to pre-release significant volumes of water for flood mitigation.  There are also potential downstream impacts that have to be considered and communicated. 

The impact of rain in a catchment is not an exact science – a small amount of rainfall can result in a large inflows and vice-versa. Significant drawdown of storage levels can only be made prior to a rainfall event once an accurate rainfall forecast is available which is generally 3-4 days in advance. This limits the volume of water which can be drawn down at short notice.

What role do G-MW dams have in flood mitigation?

The primary role of a water storage is to harvest and store customers' water entitlements, G-MW operates the dams to provide flood mitigation benefits where possible.  Generally large water storages are not designed or operated specifically for flood mitigation

The amount of flood mitigation a water storage can provide depends on a number of factors - including the operating rules of the storage, the size of the flood event, the level of water in the dam at the beginning of the event and the release capacity of the spillway.

Water storages may provide significant mitigation for small floods and may significantly reduce downstream flooding. The amount of mitigation generally reduces as the size of the flood increases, so there may be little mitigation benefit for large floods.

When did pre-releases last occur at Eildon?

G-MW last released water from Lake Eildon above normal system operating requirements (pre-release) in October 2012.     

How is water released from Eildon?

There are four ways water can be released from Eildon.

Most releases from Eildon are made through the hydro power station operated by AGL. Water is taken in through the base of the outlet tower and passed through a large conduit under the embankment to the power station. Releases up to about 20,000 ML/d are made this way. You won’t see much evidence of the releases other than some turbulent flows downstream of the dam.

The other ways water is released is through a large ‘low level’ valve adjacent to the hydro station, large ‘irrigation’ valves in the spillway or through the spillway flood gates. Generally the low level and irrigation valves are only operated as a back-up when releases can not be made through the hydro station. Releases will only be made through the spillway gates during flood events when the volume of outflow exceeds the release capacity of the hydro station.

Can we see the water being pre-released from Eildon and can we get photos?

Water is not being released across the Eildon spillway. The water is passed through the primary outlets in the Hydro power station in the same way as normal operational releases. There isn't anything different to what you would see on any normal day of the irrigation season. 

 

eildon spillway

 

The Eildon spillway is designed to pass excess flood water from the storage.
The Eildon spillway has not been used this winter.

What is a spillway and what does it do?

A spillway is a feature of a dam which is designed to pass excess flood water from the storage. Spillways are generally large concrete structures constructed beside or within the embankment. When the dams are full and inflows enter the dam the excess water is released either through the operational outlet works (for normal small flows) or over the spillway for larger flood flows.
 

Useful Links 

 

Last updated: 23 Jul 2013