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 (GMW) 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, GMW provides flood mitigation benefits where possible. Pre-releasing water from a GMW 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, Friday 19 September 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 including the delivery of environmental flows. The flows downstream of Loddon Weir will increase from 22 September to deliver an environmental flow. Flows are expected to peak at about 450 ML/d on 24 September and will remain at this rate untill 3 October. The release will gradually decrease to 100 ML/d by about 8 October.  

Lake Buffalo

Lake Buffalo is being held at an interim target of 80%. Lake Buffalo will be filled later in the season as inflows recede.

Inflows into Lake Buffalo are being passed downstream.   

Lake Nillahcootie

Lake Nillahcootie is full and spilling. 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 Eppalock

Releases from Lake Eppalock are currently meeting normal operating requirements including the delivery of environmental flows. 

For more information on Campaspe River environmental flows, please refer to the "Latest news section" of the North Central Catchment Management Authority's website : (http://www.nccma.vic.gov.au)

Lake Eildon

Releases from Lake Eildon are currently meeting normal operating requirements.

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

Last Updated: 9:30 am, 19 September 2014

Releases from Lake Eildon

Date

Month

Release (ML/d)

Yesterday 18 September 2014 1,000
Today 19 September 2014 2,500
Forecast 20 September 2014  3,500*
Forecast 21 September 2014 3.500*
Forecast 22 September 2014 4,000*

 

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 operational requirements including the delivery of environmental flows. 

The flows downstream of Goulburn Weir will increase from 22 September to deliver water for the environment. The release yesterday, today and forecast for the next ten days are mentioned below:

 

 

Last Updated: 9:30 am, 19 September 2014

Releases from Lake Eildon

Date

Month

Release (ML/d)

Yesterday 18 September 2014 910
Today 19 September 2014 910
Forecast 20 September 2014  910*
Forecast 21 September 2014 910*
Forecast 22 September 2014 1.660*
Forecast 23 September 2014 2.800*
Forecast 24 September 2014 3.000*
Forecast 25 September 2014 3,000*
Forecast 26 September 2014 3.000*
Forecast 27 September 2014 3.000*
Forecast 28 September 2014 2.200*
Forecast 29 September 2014 1.500*

 

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?

When do GMW undertake 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 GMW dams have in flood mitigation?

How is water released from Eildon?

What is a spillway and what does it do?

Are there different types of dams and what are they?

Yes.  GMW 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 GMW’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 GMW’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 GMW 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]

When do GMW undertake pre-releases?

Pre-releasing from Eildon is normal operating procedure for the dam and has been done in the past where the dam has been 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 GMW 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 GMW must adhere to. The rules limit the opportunity for GMW 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 GMW dams have in flood mitigation?

The primary role of a water storage is to harvest and store customers' water entitlements, GMW 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.

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.

eildon spillway

 

The Eildon spillway is designed to pass excess flood water from the storage.
The Eildon spillway is only used during flood events when the volume of outflow exceeds the release capacity of the hydro station.

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