Announcements
Thursday 21 November 2024
Information about managing the storage level at Lake Eildon.
Thursday 21 November 2024
Information about managing the storage level at Lake Eppalock.
Reports and Services
Operating and maintaining 23 water storages across northern Victoria that can cumulatively hold over 9,000,000 megalitres of water or 70 percent of the total water storage capacity in Victoria - is an ongoing and major part of Goulburn-Murray Water's business.
GMW closely monitors all storages, their inflow and downstream releases to ensure harvesting opportunities are maximised and stored water is managed efficiently for all our customers.
While the primary role of our water storages is to harvest and store customers' water entitlements, GMW can provide flood mitigation benefits at some storages 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.
This webpage provides information on the status of current and forecast storage releases, information on inter-valley trade transfers and estimated storage volume projections for some storages. The links above provide more detailed data and information on river levels, storage releases and any flood warnings.
Storage Releases Summary
(Update: 11:55 AM Wednesday 20 November 2024)
This information covers the status of releases from the major storages managed by GMW. The forecast releases are an indication only and may change depending on weather conditions and customer requirements. Please check this information daily if your property is subject to inundation at high river levels.
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) or access GMW's Water Status Reports (see link above).
Releases are meeting normal operating requirements, including the delivery of IVT to the Goulburn system.
Cairn Curran: Releases are meeting normal operating requirements.
Tullaroop: Releases are meeting normal operating requirements.
Laanecoorie: Releases are meeting normal operating requirements, including delivery of environmental water downstream of Loddon Weir.
The level at Lake Buffalo is currently being held close to 100% of capacity. Releases are about 330 ML/d after recent rainfall and increased inflows.
The release from Lake Eppalock is 280 ML/d to deliver IVT flows down the Campaspe River to the Murray system.
While GMW storages are not specifically for flood mitigation, Lake Eppalock does provide some flood mitigation by storing water above the full supply level and water passing over the spillway.
For more information on how the October 2022 floods occurred across the Campaspe River, visit Floods in Focus: Campaspe River System
Flow and release rates for the Campaspe River system
GMW has created a simple dashboard overview of flow and release rates for the Campaspe River system from Lake Eppalock to Rochester since October 2022.
The inflow rate at the storage includes flows from tributaries upstream of Lake Eppalock, such as the Coliban and Upper Campaspe rivers and McIvor and Wild Duck creeks.
As well as releases from Lake Eppalock, inflows from Mount Pleasant, Forest and Axe creeks contribute to flow rates along the Campaspe River downstream of the storage and Rochester.
Click the button below to be taken to the dashboard.
Campaspe River system flow and release rates dashboard
The spillway at Lake Eppalock is a fixed crest spillway, which means GMW is unable to release more water than the capacity of outlet valve of 1,600 ML/d. During spill events, downstream flows are governed by how high the storage level exceeds the full supply level.
Currently releases are meeting normal operating requirements, including transfer of water to Waranga Basin.
The release yesterday, today and a forecast for the next 4 days are outlined below:
Releases from Lake Eildon, megalitres per day. Last Updated: 11:55 AM 20 November 2024
| Yesterday |
19
|
November 2024 |
3,000 |
| Today |
20 |
November 2024 |
3,500 |
| Forecast |
21 |
November 2024 |
4,000* |
| Forecast |
22 |
November 2024 |
4,000*
|
| Forecast |
23 |
November 2024 |
4,000* |
| Forecast |
24 |
November 2024 |
4,000* |
*ctual releases from Lake Eildon may vary from those forecast at any time without notice.
What do changes in river flows mean for river levels?
The table below provides a summary of the river levels at various flow rates as measured at the gauges on the Goulburn River at Eildon, Trawool and Seymour.
Please note that the table below is specific for the river gauges at Eildon, Trawool and Seymour and the relationship between flows and river level will vary along the river as the profile changes.
This information does not relate to absolute water depth in the river however the table provides an indication of what various flows mean for river levels. For example, if flows increased from 5,000 ML/day to 6,000 ML/day, the river level at Trawool would increase by around 0.2 m.
Table of river levels at various flow rates as measured by the gauges on the Goulburn River at Eildon, Trawool and Seymour.
| 1,000 |
1.1 |
0.7 |
0.9 |
| 2,000 |
1.4 |
1.0 |
1.2 |
| 3,000 |
1.6 |
1.2 |
1.5 |
| 4,000 |
1.8 |
1.4 |
1.7 |
| 5,000 |
2.0 |
1.6 |
1.9 |
| 6,000 |
2.2 |
1.8 |
2.0 |
| 7,000 |
2.3 |
1.9 |
2.1 |
| 8,000 |
2.4 |
2.1 |
2.2 |
| 9,000 |
2.6 |
2.3 |
2.4 |
| 10,000 |
2.7 |
2.4 |
2.5 |
Please note: the table above provides an indication of the scale of typical river flows and flows may exceed 10,000 ML/day in response to rainfall in the catchment.
Flow and release rates for the Goulburn River system
GMW has created a simple dashboard overview of flow and release rates for the Goulburn River system from Lake Eildon to McCoys bridge since October 2022.
The inflow rate at the storage includes flows from tributaries upstream of Lake Eildon.
As well as releases from Lake Eildon, inflows from tributaries such as the Rubicon, Yea and Broken rivers and the Sugarloaf and Sevens creeks contribute to flow rates along the Goulburn River downstream of the storage.
Click on the button below to be taken to the dashboard.
Goulburn system flow and release rates dashboard
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.
Releases from Goulburn Weir are currently meeting normal operating requirements, including the delivery of Inter-Valley Trade (IVT) commitments to the Murray system.
The release yesterday, today and a forecast for the next 4 days are outlined below:
Releases from Goulburn Weir, megalitres per day. Last Updated: 11:55 AM 20 November 2024
| Yesterday |
19
|
November 2024 |
1,350 |
| Today |
20 |
November 2024 |
1,350 |
| Forecast |
21 |
November 2024 |
1,200* |
| Forecast |
22 |
November 2024 |
1,200* |
| Forecast |
23 |
November 2024 |
1,350* |
| Forecast |
24 |
November 2024 |
1,350* |
*Actual releases from Goulburn Weir may vary from those forecast at any time without notice.
What do changes in river flows mean for river levels?
The table below provides a summary of the river levels at various flow rates as measured at the gauges on the Goulburn River at Murchison, Shepparton and McCoy Bridge.
Please note that the table below is specific for the river gauges at Murchison, Shepparton and McCoy Bridge and the relationship between flows and river level will vary along the river as the profile changes.
This information does not relate to absolute water depth in the river however the table provides an indication of what various flows mean for river levels. For example, if flows increased from 2,000 ML/day to 3,000 ML/day, the river level at Murchison would increase by around 0.5 m.
Table of the river levels at various flow rates as measured at the gauges on the Goulburn River at Murchison, Shepparton and McCoy Bridge.
| River flow (ML/day) |
River level at Murchison (m) |
River level at Shepparton (m) |
River level at McCoy Bridge (m) |
| 1,000 |
0.9 |
2.8 |
1.5 |
| 2,000 |
1.5 |
3.1 |
2.1 |
| 3,000 |
2.0 |
3.4 |
2.6 |
| 4,000 |
2.4 |
3.7 |
3.1 |
| 5,000 |
2.8 |
4.1 |
3.5 |
| 6,000 |
3.1 |
4.4 |
4.0 |
| 7,000 |
3.5 |
4.8 |
4.4 |
| 8,000 |
3.8 |
5.1 |
4.8 |
| 9,000 |
4.1 |
5.5 |
5.2 |
| 10,000 |
4.5 |
5.9 |
5.5 |
Please note: the table above provides an indication of the scale of typical river flows and flows may exceed 10,000 ML/day in response to rainfall in the catchment.
The Goulburn River below Lake Eildon is currently operating as an unregulated system. Releases from Goulburn Weir are dependant on inflows from the streams below Lake Eildon and are continually responding to rainfall events.
The release yesterday, today and estimated forecast for the next4 days are outlined below:
|
Last Updated: 8:30 AM,6October 2016
|
Releases from Goulburn Weir
|
Date
|
Month
|
Release (ML/day)
|
| Yesterday |
5 |
October2016 |
28,000 |
| Today |
6 |
October2016 |
23,000 |
| Forecast |
7 |
October2016 |
20,000* |
| Forecast |
8 |
October 2016 |
17,000* |
| Forecast |
9 |
October2016 |
14,000* |
| Forecast |
10 |
October2016 |
11,000* |
*Actual releases from Goulburn Weir may vary from those forecast at any time without notice.
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.
What do changes in river flows mean for river levels?
The table below provides a summary of the river levels at various flow rates as measured at the gauges on the Goulburn River at Murchison, Shepparton and McCoy Bridge.
Please note that the table below is specific for the river gauges at Murchison, Shepparton and McCoy Bridge and the relationship between flows and river level will vary along the river as the profile changes.
This information does not relate to absolute water depth in the river however the table provides an indication of what various flows mean for river levels. For example, if flows increased from 2,000 ML/day to 3,000 ML/day, the river level at Murchison would increase by around 0.5 m.
| River flow (ML/day) |
River level at Murchison (m) |
River level at Shepparton (m) |
River level at McCoy Bridge(m) |
| 1,000 |
0.9 |
2.8 |
1.5 |
| 2,000 |
1.5 |
3.1 |
2.1 |
| 3,000 |
2.0 |
3.4 |
2.6 |
| 4,000 |
2.4 |
3.7 |
3.1 |
| 5,000 |
2.8 |
4.1 |
3.5 |
| 6,000 |
3.1 |
4.4 |
4.0 |
| 7,000 |
3.5 |
4.8 |
4.4 |
| 8,000 |
3.8 |
5.1 |
4.8 |
| 9,000 |
4.1 |
5.5 |
5.2 |
| 10,000 |
4.5 |
5.9 |
5.5 |
Please note: the table above provides an indication of the scale of typical river flows and flows may exceed 10,000 ML/day in response to rainfall in the catchment.
Forecast Storage Volume Projections
Climatic conditions, storage inflows and customer demands influence the volume of water held in storage throughout the year. Given the uncertainty surrounding each of these factors, exact information about future storage volumes cannot be provided or guaranteed.
Using the current storage volume, historical climate and inflow statistics, historic patterns of use and known commitments for releases in a season, storage projections under various climatic scenarios are possible.
It is important to note there are a number of underlying assumptions in the modelling used to develop the storage volume estimates and are subject to change at any time.
The storage projections are forecasts only; they are not a commitment by GMW to operate the storages to any particular scenario. The highly variable nature of climatic conditions, storage inflows and customer demands means the actual storage volume throughout the year will differ to the projections given here.
Storage volume estimates will be updated throughout the season.
Lake Eppalock
Last updated: 24 August 2015
Inter-Valley Trade Deliveries
(Last updated: 11 November 2024)
A volume of 32 GL is planned to be delivered through November 2024 to the Murray system from the Goulburn and Campaspe systems. Delivery of IVT from the Broken system to the Goulburn system has also commenced in November 2024.
Water in the Inter-Valley Trade (IVT) account is water “owed” from one river valley to another as a result of water trade.
For the Goulburn system to Murray system deliveries, an IVT delivery plan has been developed between Victoria and the Murray-Darling Basin Authority (MDBA). This plan outlines the delivery considerations and acknowledge the new Goulburn River Operating Rules which limit flow rates and pulses during peak demand periods News - Water Register.
Please be aware that under the new Goulburn trade rule, deliveries of water from the Goulburn IVT account will no longer create trade opportunity. For more information about trade rules visit the Victorian Water Register website .
The volume delivered from IVT accounts is updated in the Victorian Water Register each Wednesday morning when deliveries are occurring. To view the details of the volumes in the IVT accounts in each system, please refer to the Victorian Water Register website.
Table containing the volumes delivered in gigalitres each month from the Goulburn inter-valley trade account to the Murray system for this year and over the last 12 water years. Please note, these volumes include deliveries through Lower Broken Creek and the Campaspe River.
| 2012/13 |
0 |
0 |
0 |
0 |
0 |
53.5 |
46.2 |
0 |
0 |
0 |
0 |
0 |
99.7 |
| 2013/14 |
0 |
0 |
0 |
12.5 |
14.2 |
2.9 |
35.1 |
61.1 |
17.0 |
0 |
0 |
0 |
142.8 |
| 2014/15 |
0 |
0 |
0 |
21 |
67.4 |
21.7 |
42.9 |
36.4 |
47.4 |
3.7 |
0 |
0 |
240.6 |
| 2015/16 |
0 |
0 |
0 |
0 |
10.8 |
10.7 |
13.7 |
15.4 |
21.1 |
0 |
0 |
0 |
71.7 |
| 2016/17 |
0 |
0 |
0 |
0 |
0 |
0 |
38.2 |
29.8 |
20.5 |
21.2 |
0 |
0 |
109.7 |
| 2017/18 |
0 |
0 |
0 |
0 |
0 |
0 |
37 |
75.5 |
85.1 |
73.7 |
37.5 |
10.4 |
319.5 |
| 2018/19 |
0 |
28.2 |
27.2 |
57.6 |
27.5 |
42.1 |
82.9 |
68.9 |
50.8 |
28.2 |
19.8 |
0 |
433.4 |
| 2019/20 |
0 |
0 |
0 |
9.7 |
29.3 |
49.0 |
61.0 |
42.3 |
14.4 |
0 |
0 |
0 |
205.7 |
| 2020/21 |
0 |
0 |
0 |
0 |
27.0 |
37.2 |
37.8 |
36.4 |
39.1 |
47.3 |
40.0 |
0 |
264.8 |
| 2021/22 |
0 |
0 |
0 |
0 |
0 |
0 |
7.5 |
0 |
0 |
0 |
0 |
0 |
7.5 |
| 2022/23 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
21.3 |
6.8 |
0 |
0 |
28.1 |
| 2023/24 |
0 |
0 |
0 |
0 |
7.0 |
17.9 |
17.3 |
0 |
1.8 |
29.3 |
9.1 |
0 |
82.4 |
| 2024/25 |
0 |
30.0 |
55.0 |
|
|
|
|
|
|
|
|
|
|
Table containing the volumes delivered in megalitres each month from the Campaspe inter-valley trade account over the last 12 water years.
Table containing the volumes delivered in megalitres each month from the Loddon inter-valley trade account over the last 12 water years.
| 2012/13 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
| 2013/14 |
577 |
578 |
0 |
23 |
1,530 |
70 |
0 |
0 |
0 |
0 |
0 |
0 |
2778 |
| 2014/15 |
0 |
1,666 |
0 |
0 |
0 |
0 |
0 |
0 |
761 |
876 |
0 |
0 |
3,303 |
| 2015/16 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
1,717 |
2,937 |
0 |
0 |
4,654 |
| 2016/17 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
| 2017/18 |
0 |
0 |
220 |
940 |
0 |
0 |
0 |
0 |
140 |
0 |
0 |
0 |
1,300 |
| 2018/19 |
0 |
0 |
675 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
675 |
| 2019/20 |
0 |
0 |
0 |
50 |
6,183 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
6,234 |
| 2020/21 |
0 |
0 |
863 |
177 |
5,779 |
0 |
0 |
169 |
4,433 |
1,107 |
0 |
0 |
12,529 |
| 2021/22 |
0 |
0 |
2,269 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
2,269 |
| 2022/23 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
| 2023/24 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
| 2024/25 |
428 |
1,079 |
|
|
|
|
|
|
|
|
|
|
|
Table containing the volumes delivered in megalitres each month from the Brokeninter-valley trade account over the last 10 water years.
| 2014/15 |
0 |
0 |
0 |
0 |
653 |
590 |
913 |
1,004 |
969 |
1,388 |
0 |
0 |
5,517 |
| 2015/16 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
| 2016/17 |
0 |
0 |
0 |
0 |
0 |
160 |
69 |
1,279 |
1,494 |
1,111 |
506 |
0 |
4,619 |
| 2017/18 |
0 |
0 |
0 |
0 |
0 |
75 |
1,750 |
1,439 |
1,097 |
459 |
684 |
0 |
5,504
|
| 2018/19 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
341 |
290 |
21 |
0 |
0 |
652
|
| 2019/20 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0
|
| 2020/21 |
0 |
0 |
0 |
0 |
165 |
972 |
962 |
487 |
857 |
392 |
0 |
0 |
3,833
|
| 2021/22 |
0 |
0 |
0 |
0 |
0 |
0 |
331 |
793 |
1,172 |
128 |
0 |
0 |
2,424
|
| 2022/23 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
882 |
30 |
0 |
0 |
912
|
| 2023/24 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
0 |
774 |
784 |
270 |
0 |
1,828 |
| 2024/25 |
0 |
0 |
0 |
|
|
|
|
|
|
|
|
|
|
Forecast Storage Volume Projections
Climatic conditions, storage inflows and customer demands influence the volume of water held in storage throughout the year. Given the uncertainty surrounding each of these factors, exact information about future storage volumes cannot be provided or guaranteed.
Using the current storage volume, historical climate and inflow statistics, historic patterns of use and known commitments for releases in a season, storage projections under various climatic scenarios are possible.
Disclaimer
It is important to note there are a number of underlying assumptions in the modelling used to develop the storage volume estimates and are subject to change at any time.
The storage projections are forecasts only; they are not a commitment by GMW to operate the storages to any particular scenario. The highly variable nature of climatic conditions, storage inflows and customer demands means the actual storage volume throughout the year will differ to the projections given here.
Storage volume estimates will be updated throughout the season.
Key notes:
- Probability of exceedance (PoE) inflow percentages represents the inflow volumes that have a particular chance of being exceeded. For example the 90% PoE inflow scenario considers the storage inflow volume that has 90 chances in 100 of being exceeded - i.e. dry conditions.
- Forecast demand is based on information about water availability at the time of generating storage projection.
Lake Eildon
(Updated 20 June 2024)
Key notes:
- The scenarios shown account for operation to target filling points through winter and spring. Target filling points (as at 20 June 2024) are shown by the dashed black line. If inflows take the storage above the filling curve, GMW will proactively make releases to bring the level closer to the target filling points.
- For more information about the forecast filling points and how Lake Eildon is managed, head to www.gmwater.com.au/managing-eildon
- Probability of exceedance (PoE) inflow percentages represents the inflow volumes that have a particular chance of being exceeded. For example the 90% PoE inflow scenario considers the storage inflow volume that has 90 chances in 100 of being exceeded - i.e. dry conditions.
- Forecast demand is based on information about water availability at the time of generating storage projection.
Ovens and King System Spill Notifications
Updated: 23 August 2024
Diverters on the Ovens and King systems have spill entitlements that can be accessed each water year from 1 July until the time when the supply storage ceases to spill or pass flows above in-valley requirements.
GMW monitors storage inflow conditions and forecast when regulated releases are expected to exceed inflows, i.e. when the storage ceases to spill. The end of access to spill entitlement is usually towards the end of the calendar year, but varies depending on seasonal conditions.
GMW aim to provide 2 to 3 weeks’ notification to customers that access to spill entitlements will end for the current water year.
For customers that have lodged an order through WaterLINE, their meters are read on the date when access to spill entitlements ends. Use up to their spill entitlement is deemed and any additional use is deemed against their high-reliability water shares (HRWS). All other customer use will be deemed against their HRWS entitlement at the end of the season. Customers who have not lodged an order through WaterLINE will have all use deemed against their HRWS.
All customers are encouraged to submit all orders through WaterLINE to ensure supply can be met and accurately accounted for.
King System
King River and regulated anabranch diverters are advised that customers have access to Spill Reliability Water Shares. An announcement on the end of access to Spill Reliability Water Shares will be announced later in the season.
Ovens System
Buffalo River, Ovens River and regulated anabranch diverters are advised customers have access to Spill Reliability Water Shares. An announcement on the end of access to Spill Reliability Water Shares will be announced later in the season.
Operating Plan for delivery of water from the Goulburn Inter-Valley Trade Account
A plan for delivering water from the Goulburn Inter-Valley Trade (IVT) account to the Murray in 2022-23 has been released to support implementation of the long-term operating and trade rules introduced on 1 July 2022.
The Goulburn Operating Plan for 2022-23has been developed by the Murray-Darling Basin Authority and Victorian river operators, and the Department of Environment, Land, Water and Planning.
The plan outlines the principles and responsibilities for decision making for the delivery of water from the Goulburn Inter-Valley Trade (IVT) Account to the Murray system in 2022-23. The plan considers seasonal conditions and recognises the sustainable operating limits for summer and autumn set out in the Operating Rules for the lower Goulburn River. The operating plan also includes an operating outlook for the planned delivery of water from the Goulburn IVT account under possible climate and inflow scenarios in 2022-23.
A copy of the Plan and the Operating Rules is available from the Victorian Water Register website.
Frequently Asked Questions
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 Flood Operations Policy, opens in a new window [80 KB]
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 Flood Operations Policy, opens in a new window [80 KB]
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.
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.
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.
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.
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 generally only be made through the spillway gates during flood events when the volume of outflow exceeds the release capacity of the hydro station.
The Eildon spillway is designed to pass excess flood water from the storage.
The Eildon spillway is generally only used during flood events when the volume of outflow exceeds the release capacity of the hydro station.
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.
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
- Rainfall forecasts by the Bureau of Meteorology: